Java Multithreading Tutorial
Last Updated :
12 Aug, 2024
Threads are the backbone of multithreading. We are living in a real world which in itself is caught on the web surrounded by lots of applications. With the advancement in technologies, we cannot achieve the speed required to run them simultaneously unless we introduce the concept of multi-tasking efficiently. It is achieved by the concept of thread.
Real-life Example of Java Multithreading
Suppose you are using two tasks at a time on the computer, be it using Microsoft Word and listening to music. These two tasks are called processes . So you start typing in Word and at the same time start music app, this is called multitasking . Now you committed a mistake in a Word and spell check shows exception, this means Word is a process that is broken down into sub-processes. Now if a machine is dual-core then one process or task is been handled by one core and music is been handled by another core.
In the above example, we come across both multiprocessing and multithreading. These are somehow indirectly used to achieve multitasking. In this way the mechanism of dividing the tasks is called multithreading in which every process or task is called by a thread where a thread is responsible for when to execute, when to stop and how long to be in a waiting state. Hence, a thread is the smallest unit of processing whereas multitasking is a process of executing multiple tasks at a time.
Multitasking is being achieved in two ways :
- Multiprocessing : Process-based multitasking is a heavyweight process and occupies different address spaces in memory. Hence, while switching from one process to another, it will require some time be it very small, causing a lag because of switching. This happens as registers will be loaded in memory maps and the list will be updated.
- Multithreading : Thread-based multitasking is a lightweight process and occupies the same address space. Hence, while switching cost of communication will be very less.
Below is the Lifecycle of a Thread been illustrated
- New : When a thread is just created.
- Runnable : When a start() method is called over thread processed by the thread scheduler.
- Case A: Can be a running thread
- Case B: Can not be a running thread
- Running : When it hits case 1 means the scheduler has selected it to be run the thread from runnable state to run state.
- Blocked : When it hits case 2 meaning the scheduler has selected not to allow a thread to change state from runnable to run.
- Terminated : When the run() method exists or stop() method is called over a thread.
If we do incorporate threads in operating systems one can perceive that the process scheduling algorithms in operating systems are strongly deep-down working on the same concept incorporating thread in Gantt charts . A few of the most popular are listed below which wraps up all of them and are used practically in software development.
- First In First Out
- Last In First Out
- Round Robin Scheduling
Now Imagine the concept of Deadlock in operating systems with threads – how the switching is getting computed over internally if one only has an overview of them.
So far we have understood multithreading and thread conceptually, so we can conclude advantages of multithreading before moving to any other concept or getting to programs in multithreading.
- The user is not blocked as threads are independent even if there is an issue with one thread then only the corresponding process will be stopped rest all the operations will be computed successfully.
- Saves time as too many operations are carried over at the same time causing work to get finished as if threads are not used the only one process will be handled by the processor.
- Threads are independent though sharing the same address space.
So we have touched all main concepts of multithreading but the question striving in the head is left. why do we need it, where to use it and how? Now, we will discuss all three scenarios why multithreading is needed and where it is implemented via the help of programs in which we will be further learning more about threads and their methods. We need multithreading in four scenarios as listed.
- Thread Class
- Mobile applications
- Web applications
- Game Development
Note: By default we only have one main thread which is responsible for main thread exception as you have encountered even without having any prior knowledge of multithreading
Two Ways to Implement Multithreading
Method 1: Using Thread Class
Java provides Thread class to achieve programming invoking threads thereby some major methods of thread class are shown below in the tabular format with which we deal frequently along the action performed by them.
| Methods | Action Performed |
|---|
| isDaemon() | It checks whether the current thread is daemon or not |
| start() | It starts the execution of the thread |
| run() | It does the executable operations statements in the body of this method over a thread |
| sleep() | It is a static method that puts the thread to sleep for a certain time been passed as an argument to it |
| wait() | It sets the thread back in waiting state. |
| notify() | It gives out a notification to one thread that is in waiting state |
| notifyAll() | It gives out a notification to all the thread in the waiting state |
| setDaemon() | It set the current thread as Daemon thread |
| stop() | It is used to stop the execution of the thread |
| resume() | It is used to resume the suspended thread. |
Pre-requisites: Basic syntax and methods to deal with threads
Now let us come up with how to set the name of the thread. By default, threads are named thread-0, thread-1, and so on. But there is also a method that is often used as setName() method. Also corresponding to it there is a method getName() which returns the name of the thread be it default or settled already by using setName() method. The syntax is as follows:
Syntax:
(a) Returning the name of the thread
public String getName() ;
(b) Changing the name of the thread
public void setName(String name);
Taking a step further, let us dive into the implementation part to understand more concepts about multithreading. So, there are basically two ways of implementing multithreading:
Illustration: Consider if one has to multiply all elements by 2 and there are 500 elements in an array.
Examples
Java
// Case 1
// Java Program to illustrate Creation and execution of
// thread via start() and run() method in Single inheritance
// Class 1
// Helper thread Class extending main Thread Class
class MyThread1 extends Thread {
// Method inside MyThread2
// run() method which is called as
// soon as thread is started
public void run()
{
// Print statement when the thread is called
System.out.println("Thread1 is running");
}
}
// Class 2
// Main thread Class extending main Thread Class
class MyThread2 extends Thread {
// Method inside MyThread2
// run() method which is called
// as soon as thread is started
public void run()
{
// run() method which is called as soon as thread is
// started
// Print statement when the thread is called
System.out.println("Thread2 is running");
}
}
// Class 3
// Main Class
class GFG {
// Main method
public static void main(String[] args)
{
// Creating a thread object of our thread class
MyThread1 obj1 = new MyThread1();
MyThread2 obj2 = new MyThread2();
// Getting the threads to the run state
// This thread will transcend from runnable to run
// as start() method will look for run() and execute
// it
obj1.start();
// This thread will also transcend from runnable to
// run as start() method will look for run() and
// execute it
obj2.start();
}
}
// Case 2
// Java Program to illustrate Difference between Runnable
// & Non-runnable Threads And Single Inheritance
// Class 1
// Helper thread Class extending main Thread Class
class MyThread1 extends Thread {
// Method inside MyThread2
// run() method which is called as soon as thread is
// started
public void run() {
// Print statement when the thread is called
System.out.println("Thread 1 is running");
}
}
// Class 2
// Main thread Class extending main Thread Class
class MyThread2 extends Thread {
// Method
public void show() {
// Print statement when thread is called
System.out.println("Thread 2");
}
}
// Class 3
// Main Class
class GFG {
// Main method
public static void main(String[] args) {
// Creating a thread object of our thread class
MyThread1 obj1 = new MyThread1();
MyThread2 obj2 = new MyThread2();
// Getting the threads to the run state
// This thread will transcend from runnable to run
// as start() method will look for run() and execute
// it
obj1.start();
// This thread will now look for run() method which is absent
// Thread is simply created not runnable
obj2.start();
}
}
// Java Program to illustrate difference between
// start() method thread vs show() method
// Class 1
// Helper thread Class extending main Thread Class
class MyThread1 extends Thread {
// Method inside MyThread2
// run() method which is called as soon as thread is
// started
public void run() {
// Print statement when the thread is called
System.out.println("Thread 1 is running");
}
}
// Class 2
// Main thread Class extending main Thread Class
class MyThread2 extends Thread {
// Method
public void show() {
// Print statement when thread is called
System.out.println("Thread 2");
}
}
// Class 3
// Main Class
class GFG {
// Main method
public static void main(String[] args) {
// Creating a thread object of our thread class
MyThread1 obj1 = new MyThread1();
MyThread2 obj2 = new MyThread2();
// Getting the threads to the run state
// This thread will transcend from runnable to run
// as start() method will look for run() and execute
// it
obj1.start();
// This thread is simply a function call as
// no start() method is executed so here only
// thread is created only followed by call
obj2.show();
}
}
Output:
Case 1:
Thread1 is running
Thread2 is running
Here we have created our two thread classes for each thread. In the main method , we are simply creating objects of these thread classes where objects are now threads. So in main , we call thread using start() method over both the threads. Now start() method starts the thread and lookup for their run() method to run. Here both of our thread classes were having run() methods, so both threads are put to run state from runnable by the scheduler, and output on the console is justified.
Case 2:
Thread 1 is running
Here we have created our two thread classes for each thread. In the main method, we are simply creating objects of these thread classes where objects are now threads. So in main, we call thread using start() method over both the threads. Now start() method starts the thread and lookup their run() method to run. Here only class 1 is having the run() method to make the thread transcend from runnable to run state to execute whereas thread 2 is only created but not put to run state by the scheduler as its corresponding run() method was missing. Hence, only thread 1 is called rest thread 2 is created only and is in the runnable state later blocked by scheduler because the corresponding run() method was missing.
Case 3:
Thread 2
Thread 1 is running
Method 2: Using Runnable Interface
Another way to achieve multithreading in java is via the Runnable interface. Here as we have seen in the above example in way 1 where Thread class is extended. Here Runnable interface being a functional interface has its own run() method. Here classes are implemented to the Runnable interface. Later on, in the main() method, Runnable reference is created for the classes that are implemented in order to make bondage with Thread class to run our own corresponding run() methods.
Further, while creating an object of Thread class we will pass these references in Thread class as its constructor allows only one runnable object, which is passed as a parameter while creating Thread class object in a main() method. Now lastly just like what we did in Thread class, start() method is invoked over the runnable object who are now already linked with Thread class objects, so the execution begins for our run() methods in case of Runnable interface. It is shown in the program below as follows:
Example:
Java
// Java Program to illustrate Runnable Interface in threads
// as multiple inheritance is not allowed
// Importing basic packages
import java.io.*;
import java.util.*;
// Class 1
// Helper class implementing Runnable interface
class MyThread1 implements Runnable {
// run() method inside this class
public void run()
{
// Iterating to get more execution of threads
for (int i = 0; i < 5; i++) {
// Print statement whenever run() method
// of this class is called
System.out.println("Thread1");
// Getting sleep method in try block to
// check for any exceptions
try {
// Making the thread pause for a certain
// time using sleep() method
Thread.sleep(1000);
}
// Catch block to handle the exceptions
catch (Exception e) {
}
}
}
}
// Class 2
// Helper class implementing Runnable interface
class MyThread2 implements Runnable {
// run() method inside this class
public void run()
{
for (int i = 0; i < 5; i++) {
// Print statement whenever run() method
// of this class is called
System.out.println("Thread2");
// Getting sleep method in try block to
// check for any exceptions
try {
// Making the thread pause for a certain
// time
// using sleep() method
Thread.sleep(1000);
}
// Catch block to handle the exceptions
catch (Exception e) {
}
}
}
}
// Class 3
// Main class
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating reference of Runnable to
// our classes above in main() method
Runnable obj1 = new MyThread1();
Runnable obj2 = new MyThread2();
// Creating reference of thread class
// by passing object of Runnable in constructor of
// Thread class
Thread t1 = new Thread(obj1);
Thread t2 = new Thread(obj2);
// Starting the execution of our own run() method
// in the classes above
t1.start();
t2.start();
}
}
OutputThread2
Thread1
Thread2
Thread1
Thread2
Thread1
Thread2
Thread1
Thread2
Thread1
Points to remember: Whenever you wanted to create threads, there are only two ways:
- Extending the class
- Implementing the interface which is runnable
Make sure to create an object of threads in which you have to pass the object of runnable
Special Methods of Threads
Now let us discuss various methods that are there for threads. Here we will be discussing major methods in order to have a practical understanding of threads and multithreading which are sequential as follows:
- start() Method
- suspend() Method
- stop() Method
- wait() Method
- notify() Method
- notifyAll() Method
- sleep() Method
- Output Without sleep() Method
- Output with sleep() method in Serial Execution Processes (Blocking methods approach)
- Output with sleep() method in Parallel Execution Processes (Unblocking methods approach)
- join() Method
Note: For naive users in multithreading where threads are backbone go through Program 4 to get very basics of threads, how to start, make it hold, or terminate then only toggle to program 1 and rest as follows.
Implementation:
Java
// Example 1
// Java Program to illustrate Output Without sleep() Method
// Class 1
// Helper Class 1
class Shot extends Thread {
// Method 1
public void show() {
// Iterating to print more number of times
for (int i = 0; i < 5; i++) {
// Print statement whenever method
// of this class is called
System.out.println("Shot");
}
}
}
// Class 2
// Helper Class 2
class Miss extends Thread {
// Method 2
public void show() {
// Iterating to print more number of times
for (int i = 0; i < 5; i++) {
// Print statement whenever method
// of this class is called
System.out.println("Miss");
}
}
}
// Class 3
// Main class
public class GFG {
// Method 3
// Main method
public static void main(String[] args) {
// Creating objects in the main() method
// of class 1 and class 2
Shot obj1 = new Shot();
Miss obj2 = new Miss();
// Calling methods of the class 1 and class 2
obj1.show();
obj2.show();
}
}
// Example 2
// Java Program to illustrate Output Using sleep() Method
// in Serial Execution
// Class 1
// Helper Class 1
class Shot extends Thread {
// Method 1
// public void show() {
public void show()
{
// Iterating to print more number of times
for (int i = 0; i < 5; i++) {
// Print statement
System.out.println("Shot");
// Making thread to sleep using sleep() method
// Try-catch block for exceptions
try {
Thread.sleep(1000);
}
catch (Exception e) {
}
}
}
}
// Class 2
// Helper Class 2 Hello
class Miss extends Thread {
// Method 2
// public void show() {
public void show()
{
// Iterating to print more number of times
for (int i = 0; i < 5; i++) {
// Print statement
System.out.println("Miss");
// Making thread to sleep using sleep() method
// Try-catch block for exceptions
try {
Thread.sleep(1000);
}
catch (Exception e) {
}
}
}
}
// Class 3
// Main class
public class GFG {
// Method 3
// Main method
public static void main(String[] args)
{
// Creating objects in the main() method
Shot obj1 = new Shot();
Miss obj2 = new Miss();
// Starting the thread objects
obj1.start();
obj2.start();
// Calling methods of class 1 and class 2
obj1.show();
obj2.show();
}
}
// Example 3
// Java Program to illustrate Output Using sleep() Method
// in Parallel Execution
// Class 1
// Helper Class 1
class Shot extends Thread {
// Method 1
// public void show() {
public void run()
{
// Iterating to print more number of times
for (int i = 0; i < 5; i++) {
// Print statement
System.out.println("Shot");
// Making thread to sleep using sleep() method
// Try catch block for exceptions
try {
Thread.sleep(1000);
}
catch (Exception e) {
}
}
}
}
// Class 2
// Helper Class 2 Hello
class Miss extends Thread {
// Method 2
// public void show() {
public void run()
{
// Iterating to print more number of times
for (int i = 0; i < 5; i++) {
// Print statement
System.out.println("Miss");
// Making thread to sleep using sleep() method
// Try catch block for exceptions
try {
Thread.sleep(1000);
}
catch (Exception e) {
}
}
}
}
// Class 3
// Main class
public class GFG {
// Method 3
// Main method
public static void main(String[] args)
{
// Creating objects in the main() method
Shot obj1 = new Shot();
Miss obj2 = new Miss();
// Starting the thread objects
// using start() method
// start() method calls the run() method
// automatically
obj1.start();
obj2.start();
}
}
Output:
Case 1:
Shot
Shot
Shot
Shot
Shot
Miss
Miss
Miss
Miss
Miss
Case 2: V ideo output
Shot
Shot
Shot
Shot
Shot
Miss
Miss
Miss
Miss
Miss
Case 3: Video output
Shot
Miss
Shot
Miss
Shot
Miss
Shot
Miss
Shot
Miss
Note: There is no priority been set for threads for which as per the order of execution of threads outputs will vary so do remember this drawback of multithreading of different outputs leading to data inconsistency issues which we will be discussing in-depth in the later part under synchronization in threads.
Priorities in Threads
Priorities in threads is a concept where each thread is having a priority which is represented by numbers ranging from 1 to 10.
- The default priority is set to 5 as excepted.
- Minimum priority is set to 1.
- Maximum priority is set to 10.
Here 3 constants are defined in it namely as follows:
- public static int NORM_PRIORITY
- public static int MIN_PRIORITY
- public static int MAX_PRIORITY
Let us discuss it with an example to get how internally the work is getting executed. Here we will be using the knowledge gathered above as follows:
- We will use currentThread() method to get the name of the current thread. User can also use setName() method if he/she wants to make names of thread as per choice for understanding purposes.
- getName() method will be used to get the name of the thread.
Java
// Java Program to illustrate Priority Threads
// Case 1: No priority is assigned (Default priority)
// Importing input output thread class
import java.io.*;
// Importing Thread class from java.util package
import java.util.*;
// Class 1
// Helper Class (Our thread class)
class MyThread extends Thread {
public void run()
{
// Printing the current running thread via getName()
// method using currentThread() method
System.out.println("Running Thread : "
+ currentThread().getName());
// Print and display the priority of current thread
// via currentThread() using getPriority() method
System.out.println("Running Thread Priority : "
+ currentThread().getPriority());
}
}
// Class 2
// Main Class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating objects of MyThread(above class)
// in the main() method
MyThread t1 = new MyThread();
MyThread t2 = new MyThread();
// Case 1: Default Priority no setting
t1.start();
t2.start();
}
}
// Java Program to illustrate Priority Threads
// Case 2: NORM_PRIORITY
// Importing input output thread class
import java.io.*;
// Importing Thread class from java.util package
import java.util.*;
// Class 1
// Helper Class (Our thread class)
class MyThread extends Thread {
// run() method to transit thread from
// runnable to run state
public void run()
{
// Printing the current running thread via getName()
// method using currentThread() method
System.out.println("Running Thread : "
+ currentThread().getName());
// Print and display the priority of current thread
// via currentThread() using getPriority() method
System.out.println("Running Thread Priority : "
+ currentThread().getPriority());
}
}
// Class 2
// Main Class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating objects of MyThread(above class)
// in the main() method
MyThread t1 = new MyThread();
MyThread t2 = new MyThread();
// Setting priority to thread via NORM_PRIORITY
// which set priority to 5 as default thread
t1.setPriority(Thread.NORM_PRIORITY);
t2.setPriority(Thread.NORM_PRIORITY);
// Setting default priority using
// NORM_PRIORITY
t1.start();
t2.start();
}
}
// Java Program to illustrate Priority Threads
// Case 3: MIN_PRIORITY
// Importing input output thread class
import java.io.*;
// Importing Thread class from java.util package
import java.util.*;
// Class 1
// Helper Class (Our thread class)
class MyThread extends Thread {
// run() method to transit thread from
// runnable to run state
public void run()
{
// Printing the current running thread via getName()
// method using currentThread() method
System.out.println("Running Thread : "
+ currentThread().getName());
// Print and display the priority of current thread
// via currentThread() using getPriority() method
System.out.println("Running Thread Priority : "
+ currentThread().getPriority());
}
}
// Class 2
// Main Class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating objects of MyThread(above class)
// in the main() method
MyThread t1 = new MyThread();
MyThread t2 = new MyThread();
// Setting priority to thread via NORM_PRIORITY
// which set priority to 1 as least priority thread
t1.setPriority(Thread.MIN_PRIORITY);
t2.setPriority(Thread.MIN_PRIORITY);
// Setting default priority using
// NORM_PRIORITY
t1.start();
t2.start();
}
}
// Java Program to illustrate Priority Threads
// Case 4: MAX_PRIORITY
// Importing input output thread class
import java.io.*;
// Importing Thread class from java.util package
import java.util.*;
// Class 1
// Helper Class (Our thread class)
class MyThread extends Thread {
// run() method to transit thread from
// runnable to run state
public void run()
{
// Printing the current running thread via getName()
// method using currentThread() method
System.out.println("Running Thread : "
+ currentThread().getName());
// Print and display the priority of current thread
// via currentThread() using getPriority() method
System.out.println("Running Thread Priority : "
+ currentThread().getPriority());
}
}
// Class 2
// Main Class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating objects of MyThread(above class)
// in the main() method
MyThread t1 = new MyThread();
MyThread t2 = new MyThread();
// Setting priority to thread via MAX_PRIORITY
// which set priority to 10 as most priority thread
t1.setPriority(Thread.MAX_PRIORITY);
t2.setPriority(Thread.MAX_PRIORITY);
// Setting default priority using
// MAX_PRIORITY
// Starting the threads using start() method
// which automatically invokes run() method
t1.start();
t2.start();
}
}
Output:
Case 1: Default Priority
Running Thread : Thread-0
Running Thread : Thread-1
Running Thread Priority : 5
Running Thread Priority : 5
Case 2: NORM_PRIORITY
Running Thread : Thread-0
Running Thread : Thread-1
Running Thread Priority : 5
Running Thread Priority : 5
Case 3: MIN_PRIORITY
Running Thread : Thread-0
Running Thread : Thread-1
Running Thread Priority : 1
Running Thread Priority : 1
Case 4: MAX_PRIORITY
Running Thread : Thread-1
Running Thread : Thread-0
Running Thread Priority : 10
Running Thread Priority : 10
Output Explanation :
If we look carefully we do see the outputs for cases 1 and 2 are equivalent. This signifies that when the user is not even aware of the priority threads still NORM_PRIORITY is showcasing the same result as to what default priority is. It is because the default priority of running thread as soon as the corresponding start() method is called is executed as per setting priorities for all the thread to 5 which is equivalent to the priority of NORM case. This is because both the outputs are equivalent to each other. While in case 3 priority is set to a minimum on a scale of 1 to 10 so do the same in case 4 where priority is assigned to 10 on the same scale.
Hence, all the outputs in terms of priorities are justified. Now let us move ahead onto an important aspect of priority threading been incorporated in daily life – Daemon thread
Daemon thread is basically a service provider thread that provides services to the user thread. The scope for this thread start() or be it terminate() is completely dependent on the user’s thread as it supports in the backend for user threads being getting run. As soon as the user thread is terminated daemon thread is also terminated at the same time as being the service provider thread.
Hence, the characteristics of the Daemon thread are as follows:
- It is only the service provider thread not responsible for interpretation in user threads.
- So, it is a low-priority thread.
- It is a dependent thread as it has no existence on its own.
- JVM terminates the thread as soon as user threads are terminated and come back into play as the user’s thread starts.
- Yes, you guess the most popular example is garbage collector in java. Some other examples do include ‘finalizer’.
Exceptions: IllegalArgumentException as return type while setting a Daemon thread is boolean so do apply carefully.
Note: To get rid of the exception users thread should only start after setting it to daemon thread. The other way of starting prior setting it to daemon will not work as it will pop-out IllegalArgumentException
As discussed above in the Thread class two most widely used method is as follows:
| Daemon Thread Methods | Action Performed |
|---|
| isDaemon() | It checks whether the current thread is a daemon thread or not |
| setDaemon() | It set the thread to be marked as daemon thread |
Let us discuss the implementation of the Daemon thread before jumping onto the garbage collector.
Java
// Java Program to show Working of Daemon Thread
// with users threads
import java.io.*;
// Importing Thread class from java.util package
import java.util.*;
// Class 1
// Helper Class extending Thread class
class CheckingMyDaemonThread extends Thread {
// Method
// run() method which is invoked as soon as
// thread start via start()
public void run()
{
// Checking whether the thread is daemon thread or
// not
if (Thread.currentThread().isDaemon()) {
// Print statement when Daemon thread is called
System.out.println(
"I am daemon thread and I am working");
}
else {
// Print statement whenever users thread is
// called
System.out.println(
"I am user thread and I am working");
}
}
}
// Class 2
// Main Class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating threads in the main body
CheckingMyDaemonThread t1
= new CheckingMyDaemonThread();
CheckingMyDaemonThread t2
= new CheckingMyDaemonThread();
CheckingMyDaemonThread t3
= new CheckingMyDaemonThread();
// Setting thread named 't2' as our Daemon thread
t2.setDaemon(true);
// Starting all 3 threads using start() method
t1.start();
t2.start();
t3.start();
// Now start() will automatically
// invoke run() method
}
}
// Java Program to show Working of Daemon Thread
// with users threads where start() is invoked
// prior before setting thread to Daemon
import java.io.*;
// Basically we are importing Thread class
// from java.util package
import java.util.*;
// Class 1
// Helper Class extending Thread class
class CheckingMyDaemonThread extends Thread {
// Method
// run() method which is invoked as soon as
// thread start via start()
public void run()
{
// Checking whether the thread is daemon thread or
// not
if (Thread.currentThread().isDaemon()) {
// Print statement when Daemon thread is called
System.out.println(
"I am daemon thread and I am working");
}
else {
// Print statement whenever users thread is
// called
System.out.println(
"I am user thread and I am working");
}
}
}
// Class 2
// Main Class
class GFG {
// Method
// Main driver method
public static void main(String[] args)
{
// Creating threads objects of above class
// in the main body
CheckingMyDaemonThread t1
= new CheckingMyDaemonThread();
CheckingMyDaemonThread t2
= new CheckingMyDaemonThread();
CheckingMyDaemonThread t3
= new CheckingMyDaemonThread();
// Starting all 3 threads using start() method
t1.start();
t2.start();
t3.start();
// Now start() will automatically invoke run()
// method
// Now at last setting already running thread 't2'
// as our Daemon thread will throw an exception
t2.setDaemon(true);
}
}
Another way to achieve the same is through Thread Group in which as the name suggests multiple threads are treated as a single object and later on all the operations are carried on over this object itself aiding in providing a substitute for the Thread Pool.
Note:
While implementing ThreadGroup do note that ThreadGroup is a part of ‘ java.lang.ThreadGroup’ class not a part of Thread class in java so do peek out constructors and methods of ThreadGroup class before moving ahead keeping a check over deprecated methods in his class so as not to face any ambiguity further.
Here main() method in itself is a thread because of which you do see Exception in main() while running the program because of which system.main thread exception is thrown sometimes while execution of the program.
Synchronization
It is the mechanism that bounds the access of multiple threads to share a common resource hence is suggested to be useful where only one thread at a time is granted the access to run over.
It is implemented in the program by using ‘ synchronized ‘ keyword.
Now let’s finally discuss some advantages and disadvantages of synchronization before implementing the same. For more depth in synchronization, one can also learn object level lock and class level lock and do notice the differences between two to get a fair understanding of the same before implementing the same.
Why Synchronization is Required?
- Data inconsistency issues are the primary issue where multiple threads are accessing the common memory which sometimes results in faults in order to avoid that a thread is overlooked by another thread if it fails out.
- Data integrity
- To work with a common shared resource which is very essential in the real world such as in banking systems.
Note: Do not go for synchronized keyword unless it is most needed, remember this as there is no priority setup for threads, so if the main thread runs before or after other thread the output of the program would be different.
The biggest advantage of synchronization is the increase in idiotic resistance as one can not choose arbitrarily an object to lock on as a result string literal can not be locked or be the content. Hence, these bad practices are not possible to perform on synchronized method block.
As we have seen humongous advantages and get to know how important it is but there comes disadvantage with it.
Disadvantage: Performance issues will arise as during the execution of one thread all the other threads are put to a blocking state and do note they are not in waiting state . This causes a performance drop if the time taken for one thread is too long.
multi-tasking
As perceived from the image in which we are getting that count variable being shared resource is updating randomly. It is because of multithreading for which this concept becomes a necessity.
- Case 1: If ‘ main thread’ executes first then count will be incremented followed by a ‘ thread T’ in synchronization
- Case 2: If ‘ thread T ‘ executes first then count will not increment followed by ‘ main thread ‘ in synchronization
Implementation: Let us take a sample program to observe this 0 1 count conflict
Example:
Java
// Java Program to illustrate Output Conflict between
// Execution of Main thread vs Thread created
// count = 1 if main thread executes first
// count = 1 if created thread executes first
// Importing basic required libraries
import java.io.*;
import java.util.*;
// Class 1
// Helper Class extending Thread class
class MyThread extends Thread {
// Declaring and initializing initial count to zero
int count = 0;
// Method 1
// To increment the count above by unity
void increment() { count++; }
// Method 2
// run method for thread invoked after
// created thread has started
public void run()
{
// Call method in this method
increment();
// Print and display the count
System.out.println("Count : " + count);
}
}
// Class 2
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating the above our Thread class object
// in the main() method
MyThread t1 = new MyThread();
// start() method to start execution of created
// thread that will look for run() method
t1.start();
}
}
Output:
Output Explanation:
Here the count is incremented to 1 meaning ‘ main thread ‘ has executed prior to ‘ created thread ‘. We have run it many times and compiled and run once again wherein all cases here main thread is executing faster than created thread but do remember output may vary. Our created thread can execute prior to ‘ main thread ‘ leading to ‘Count : 0’ as an output on the console.
Now another topic that arises in dealing with synchronization in threads is Thread safety in java synchronization is the new concept that arises out in synchronization so let us discuss it considering
- A real-life scenario followed by
- Pictorial representation as an illustration followed by
- Technically description and implementation
Real-life Scenario
Suppose a person is withdrawing some amount of money from the bank and at the same time the ATM card registered with the same account number is carrying on withdrawal operation by some other user. Now suppose if withdrawing some amount of money from net banking makes funds in account lesser than the amount which needed to be withdrawal or the other way. This makes the bank unsafe as more funds are debited from the account than was actually present in the account making the bank very unsafe and is not seen in daily life. So what banks do is that they only let one transaction at a time. Once it is over then another is permitted.
Illustration:
Interpreting the same technology as there are two different processes going on which object in case of parallel execution is over headed by threads. Now possessing such traits over threads such that they should look after for before execution or in simpler words making them synchronized. This mechanism is referred to as Thread Safe with the use of the keyword ‘ synchronized ‘ before the common shared method/function to be performed parallel.
Technical Description:
As we know Java has a feature, Multithreading , which is a process of running multiple threads simultaneously. When multiple threads are working on the same data, and the value of our data is changing, that scenario is not thread-safe, and we will get inconsistent results. When a thread is already working on an object and preventing another thread from working on the same object, this process is called Thread-Safety. Now there are several ways to achieve thread-safety in our program namely as follows:
- Using Synchronization
- Using Volatile Keyword
- Using Atomic Variable
- Using Final Keyword
Conclusion: Hence, if we are accessing one thread at a time then we can say thread-safe program and if multiple threads are getting accessed then the program is said to be thread-unsafe that is one resource at a time can not be shared by multiple threads at a time.
Implementation:
- Java Program to illustrate Incomplete Thread Iterations returning counter value to Zero irrespective of iteration bound
- Java Program to Illustrate Complete Thread Iterations illustrating join() Method
- Java Program to Illustrate thread-unsafe or non-synchronizing programs as of incomplete iterations
- Java Program to Illustrate Thread Safe And synchronized Programs as of Complete iterations using ‘ synchronized ‘ Keyword.
Examples
Java
// Example 1
// Java Program to illustrate Incomplete Thread Iterations
// Returning Counter Value to Zero
// irrespective of iteration bound
// Importing input output classes
import java.io.*;
// Class 1
// Helper Class
class TickTock {
// Member variable of this class
int count;
// Method of this Class
// It increments counter value whenever called
public void increment()
{
// Increment count by unity
// i.e count = count + 1;
count++;
}
//
}
// Class 2
// Synchronization demo class
// Main Class
class GFG {
// Main driver method
public static void main(String[] args) throws Exception
{
// Creating an object of class TickTock in main()
TickTock tt = new TickTock();
// Now, creating an thread object
// using Runnable interface
Thread t1 = new Thread(new Runnable() {
// Method
// To begin the execution of thread
public void run()
{
// Expression
for (int i = 0; i < 10000; i++) {
// Calling object of above class
// in main() method
tt.increment();
}
}
});
// Making above thread created to start
// via start() method which automatically
// calls run() method in Ticktock class
t1.start();
// Print and display the count
System.out.println("Count : " + tt.count);
}
}
// Example 2
// Java Program to Illustrate Complete Thread Iterations
// illustrating join() Method
// Importing input output classes
import java.io.*;
// Class 1
// Helper Class
class TickTock {
// Member variable of this class
int count;
// Method of this Class
public void increment()
{
// Increment count by unity
// whenever this function is called
count++;
}
}
// Class 2
// Synchronization demo class
// Main Class
class GFG {
// Main driver method
public static void main(String[] args) throws Exception
{
// Creating an object of class TickTock in main()
TickTock tt = new TickTock();
// Now, creating an thread object
// using Runnable interface
Thread t1 = new Thread(new Runnable() {
// Method
// To begin the execution of thread
public void run()
{
// Expression
for (int i = 0; i < 1000; i++) {
// Calling object of above class
// in main() method
tt.increment();
}
}
});
// Making above thread created to start
// via start() method which automatically
// calls run() method
t1.start();
// Now we are making main() thread to wait so
// that thread t1 completes it job
// using join() method
t1.join();
// Print and display the count value
System.out.println("Count : " + tt.count);
}
}
// Example 3
// Java Program to Illustrate Thread Unsafe Or
// Non-synchronizing Programs as of Incomplete Iterations
// Without using 'synchronized' program
// Importing input output classes
import java.io.*;
// Class 1
// Helper Class
class TickTock {
// Member variable of this class
int count;
// Method of this Class
public void increment()
{
// Increment count by unity
count++;
}
}
// Class 2
// Synchronization demo class
// Main Class
class GFG {
// Main driver method
public static void main(String[] args) throws Exception
{
// Creating an object of class TickTock in main()
TickTock tt = new TickTock();
// Now, creating an thread object
// using Runnable interface
Thread t1 = new Thread(new Runnable() {
// Method
// To begin the execution of thread
public void run()
{
// Expression
for (int i = 0; i < 100000; i++) {
// Calling object of above class
// in main() method
tt.increment();
}
}
});
// Now creating another thread and lets check
// how they increment count value running parallelly
// Thread 2
Thread t2 = new Thread(new Runnable() {
// Method
// To begin the execution of thread
public void run()
{
// Expression
for (int i = 0; i < 100000; i++) {
// Calling object of above class
// in main() method
tt.increment();
}
}
});
// Making above thread created to start
// via start() method which automatically
// calls run() method
t1.start();
t2.start();
// Now we are making main() thread to wait so
// that thread t1 completes it job
t1.join();
t2.join();
// Print and display the count
System.out.println("Count : " + tt.count);
}
}
// Example 4
// Java Program to Illustrate Thread Safe And
// Synchronized Programs as of Complete Iterations
// using 'synchronized' Keyword
// Importing input output classes
import java.io.*;
// Class 1
// helper Class
class TickTock {
// Member variable of this class
int count;
// Method of this Class
public synchronized void increment()
{
// Increment count by unity
count++;
}
//
}
// Class 2
// Synchronization demo class
// Main Class
class GFG {
// Main driver method
public static void main(String[] args) throws Exception
{
// Creating an object of class TickTock in main()
TickTock tt = new TickTock();
// Now, creating an thread object
// using Runnable interface
Thread t1 = new Thread(new Runnable() {
// Method
// To begin the execution of thread
public void run()
{
// Expression
for (int i = 0; i < 100000; i++) {
// Calling object of above class
// in main() method
tt.increment();
}
}
});
// Thread 2
Thread t2 = new Thread(new Runnable() {
// Method
// To begin the execution of thread
public void run()
{
// Expression
for (int i = 0; i < 100000; i++) {
// Calling object of above class
// in main() method
tt.increment();
}
}
});
// Making above thread created to start
// via start() method which automatically
// calls run() method
t1.start();
t2.start();
// Now we are making main() thread to wait so
// that thread t1 completes it job
t1.join();
t2.join();
// Print and display the count
System.out.println("Count : " + tt.count);
}
}
Output:
Case 1
Count : 0
Case 2
Count : 10000
Case 3
Count : 151138
Case 4
Count : 200000
Output Explanation:
In case 1 we can see that count is zero as initialized. Now we have two threads main thread and the thread t1. So there are two threads so now what happens sometimes instance is shared among both of the threads.
In case 1 both are accessing the count variable where we are directly trying to access thread via thread t1.count which will throw out 0 always as we need to call it with the help of object to perform the execution.
Now we have understood the working of synchronization is a thread that is nothing but referred to as a term Concurrency in java which in layman language is executing multiple tasks. Let us depict concurrency in threads with the help of a pictorial illustration.
Consider the task of multiplying an array of elements by a multiplier of 2. Now if we start multiplying every element randomly wise it will take a serious amount of time as every time the element will be searched over and computer. By far we have studied multithreading above in which we have concluded to a single line that thread is the backbone of multithreading.
So incorporating threads in the above situation as the machine is quad-core we here take 4 threads for every core where we divide the above computing sample set to (1/4) th resulting out in 4x faster computing. If in the above scenario it had taken 4 seconds then now it will take 1 second only. This mechanism of parallel running threads in order to achieve faster and lag-free computations is known as concurrency.
Note: Go for multithreading always for concurrent execution and if not using this concept go for sequential execution despite having bigger chunks of code as safety to our code is the primary issue.
Conclusion
Understanding Java Multithreading is important for creating fast and efficient applications. By using multithreading, you can run multiple tasks at the same time, making your programs more responsive and powerful. Key ideas like thread synchronization, concurrent collections, and the executor framework help manage multiple threads safely. In the above article we have described all details about Java multithreading.
Java Multithreading Tutorial – FAQs
What is multithreading in Java?
Multithreading in Java refers to the ability of a program to execute multiple threads concurrently. This allows the program to perform multiple tasks simultaneously, which can improve performance and responsiveness.
Why is multithreading important in Java?
Multithreading is important in Java because it allows developers to create more responsive and efficient applications. By dividing tasks into threads, a program can take advantage of multiple CPU cores and perform tasks in parallel.
How to create a thread in Java?
In Java, a thread can be created by extending the Thread class or implementing the Runnable interface. This allows developers to define the code that will be executed in the new thread.
What are the benefits of multithreading in Java?
Multithreading in Java offers several benefits, including improved performance, better resource utilization, enhanced responsiveness, and the ability to handle multiple tasks concurrently.
Are there any challenges in multithreading in Java?
Yes, multithreading in Java can introduce challenges such as thread synchronization, deadlock, and thread safety. Developers need to carefully design and manage their multithreaded programs to avoid these issues.
What is the difference between multitasking and multithreading in Java?
Multitasking refers to the ability of an operating system to execute multiple tasks concurrently, while multithreading is the ability of a program to perform multiple tasks concurrently within the same process. In Java, multithreading is a way to achieve multitasking.
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In Java, classes and objects are basic concepts of Object Oriented Programming (OOPs) that are used to represent real-world concepts and entities. The class represents a group of objects having similar properties and behavior. For example, the animal type Dog is a class while a particular dog named
11 min read
Java Constructors
Java constructors or constructors in Java is a terminology used to construct something in our programs. A constructor in Java is a special method that is used to initialize objects. The constructor is called when an object of a class is created. It can be used to set initial values for object attrib
9 min read
Object Class in Java
Object class in Java is present in java.lang package. Every class in Java is directly or indirectly derived from the Object class. If a class does not extend any other class then it is a direct child class of the Java Object class and if it extends another class then it is indirectly derived. The Ob
8 min read
Abstraction in Java
Abstraction in Java is the process in which we only show essential details/functionality to the user. The non-essential implementation details are not displayed to the user. In this article, we will learn about abstraction and what abstraction means. Simple Example to understand Abstraction:Televisi
11 min read
Encapsulation in Java
Encapsulation in Java is a fundamental concept in object-oriented programming (OOP) that refers to the bundling of data and methods that operate on that data within a single unit, which is called a class in Java. Java Encapsulation is a way of hiding the implementation details of a class from outsid
8 min read
Inheritance in Java
Java, Inheritance is an important pillar of OOP(Object-Oriented Programming). It is the mechanism in Java by which one class is allowed to inherit the features(fields and methods) of another class. In Java, Inheritance means creating new classes based on existing ones. A class that inherits from ano
13 min read
Polymorphism in Java
The word 'polymorphism' means 'having many forms'. In simple words, we can define Java Polymorphism as the ability of a message to be displayed in more than one form. In this article, we will learn what is polymorphism and its type. Real-life Illustration of Polymorphism in Java: A person can have d
6 min read
Method Overloading in Java
In Java, Method Overloading allows different methods to have the same name, but different signatures where the signature can differ by the number of input parameters or type of input parameters, or a mixture of both. Method overloading in Java is also known as Compile-time Polymorphism, Static Polym
9 min read
Overriding in Java
In Java, Overriding is a feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its super-classes or parent classes. When a method in a subclass has the same name, the same parameters or signature, and the same return type(or
13 min read
Packages In Java
Package in Java is a mechanism to encapsulate a group of classes, sub packages and interfaces. Packages are used for: Preventing naming conflicts. For example there can be two classes with name Employee in two packages, college.staff.cse.Employee and college.staff.ee.EmployeeMaking searching/locatin
8 min read
Java Interfaces
Interfaces in Java
An Interface in Java programming language is defined as an abstract type used to specify the behavior of a class. An interface in Java is a blueprint of a behavior. A Java interface contains static constants and abstract methods. What are Interfaces in Java?The interface in Java is a mechanism to ac
11 min read
Interfaces and Inheritance in Java
A class can extend another class and can implement one and more than one Java interface. Also, this topic has a major influence on the concept of Java and Multiple Inheritance. Example: [GFGTABS] Java //Driver Code Starts{ // A class can implement multiple interfaces import java.io.*; //Driver Code
7 min read
Java Class vs Interfaces
In Java, the difference between a class and an interface is syntactically similar, both contain methods and variables, but they are different in many aspects. The main difference is, A class defines the state of behavior of objects.An interface defines the methods that a class must implement.Class v
5 min read
Java Functional Interfaces
A functional interface in Java is an interface that contains only one abstract method. Functional interfaces can have multiple default or static methods, but only one abstract method. Runnable, ActionListener, and Comparator are common examples of Java functional interfaces. From Java 8 onwards, lam
7 min read
Nested Interface in Java
We can declare interfaces as members of a class or another interface. Such an interface is called a member interface or nested interface. Interfaces declared outside any class can have only public and default (package-private) access specifiers. In Java, nested interfaces (interfaces declared inside
5 min read
Marker interface in Java
It is an empty interface (no field or methods). Examples of marker interface are Serializable, Cloneable and Remote interface. All these interfaces are empty interfaces. public interface Serializable { // nothing here } Examples of Marker Interface which are used in real-time applications : Cloneabl
3 min read
Comparator Interface in Java with Examples
A comparator interface is used to order the objects of user-defined classes. A comparator object is capable of comparing two objects of the same class. Following function compare obj1 with obj2. Syntax: public int compare(Object obj1, Object obj2):Suppose we have an Array/ArrayList of our own class
6 min read
Java Collections
Collections in Java
Any group of individual objects that are represented as a single unit is known as a Java Collection of Objects. In Java, a separate framework named the "Collection Framework" has been defined in JDK 1.2 which holds all the Java Collection Classes and Interface in it. In Java, the Collection interfac
15+ min read
Collections Class in Java
Collections class in Java is one of the utility classes in Java Collections Framework. The java.util package contains the Collections class in Java. Java Collections class is used with the static methods that operate on the collections or return the collection. All the methods of this class throw th
13 min read
Collection Interface in Java
The Collection interface in Java is a core member of the Java Collections Framework located in the java.util package. It is one of the root interfaces of the Java Collection Hierarchy. The Collection interface is not directly implemented by any class. Instead, it is implemented indirectly through it
6 min read
Java List Interface
The List Interface in Java extends the Collection Interface and is a part of java.util package. It is used to store the ordered collections of elements. So in a Java List, you can organize and manage the data sequentially. Maintained the order of elements in which they are added.Allows the duplicate
15+ min read
ArrayList in Java
Java ArrayList is a part of collections framework and it is a class of java.util package. It provides us with dynamic arrays in Java. Though, it may be slower than standard arrays but can be helpful in programs where lots of manipulation in array is required. The main advantage of ArrayList is, unli
10 min read
Vector Class in Java
The Vector class implements a growable array of objects. Vectors fall in legacy classes, but now it is fully compatible with collections. It is found in java.util package and implement the List interface. Thread-Safe: All methods are synchronized, making it suitable for multi-threaded environments.
13 min read
LinkedList in Java
Linked List is a part of the Collection framework present in java.util package. This class is an implementation of the LinkedList data structure which is a linear data structure where the elements are not stored in contiguous locations and every element is a separate object with a data part and addr
13 min read
Stack Class in Java
Java Collection framework provides a Stack class that models and implements a Stack data structure. The class is based on the basic principle of LIFO(last-in-first-out). In addition to the basic push and pop operations, the class provides three more functions of empty, search, and peek. The Stack cl
11 min read
Set in Java
The Set Interface is present in java.util package and extends the Collection interface. It is an unordered collection of objects in which duplicate values cannot be stored. It is an interface that implements the mathematical set. This interface adds a feature that restricts the insertion of the dupl
14 min read
Java HashSet
HashSet in Java implements the Set interface of Collections Framework. It is used to store the unique elements and it doesn't maintain any specific order of elements. Can store the Null values.Uses HashMap (implementation of hash table data structure) internally.Also implements Serializable and Clon
12 min read
TreeSet in Java
TreeSet is one of the most important implementations of the SortedSet interface in Java that uses a Tree(red - black tree) for storage. The ordering of the elements is maintained by a set using their natural ordering whether or not an explicit comparator is provided. This must be consistent with equ
13 min read
Java LinkedHashSet
LinkedHashSet in Java implements the Set interface of the Collection Framework. It combines the functionality of a HashSet with a LinkedList to maintain the insertion order of elements. Stores unique elements only.Maintains insertion order.Provides faster iteration compared to HashSet.Allows null el
8 min read
Queue Interface In Java
The Queue Interface is present in java.util package and extends the Collection interface. It stores and processes the data in FIFO(First In First Out) order. It is an ordered list of objects limited to inserting elements at the end of the list and deleting elements from the start of the list. No Nul
13 min read
PriorityQueue in Java
The PriorityQueue class in Java is part of the java.util package. It is known that a Queue follows the FIFO(First-In-First-Out) Algorithm, but the elements of the Queue are needed to be processed according to the priority, that's when the PriorityQueue comes into play. The PriorityQueue is based on
11 min read
Deque Interface in Java
Deque Interface present in java.util package is a subtype of the queue interface. The Deque is related to the double-ended queue that supports adding or removing elements from either end of the data structure. It can either be used as a queue(first-in-first-out/FIFO) or as a stack(last-in-first-out/
10 min read
Map Interface in Java
In Java, Map Interface is present in the java.util package represents a mapping between a key and a value. Java Map interface is not a subtype of the Collection interface. Therefore it behaves a bit differently from the rest of the collection types. No Duplicates in Keys: Ensures that keys are uniqu
12 min read
HashMap in Java
In Java, HashMap is part of the Java Collections Framework and is found in the java.util package. It provides the basic implementation of the Map interface in Java. HashMap stores data in (key, value) pairs. Each key is associated with a value, and you can access the value by using the corresponding
15+ min read
Java LinkedHashMap
LinkedHashMap in Java implements the Map interface of the Collections Framework. It stores key-value pairs while maintaining the insertion order of the entries. It maintains the order in which elements are added. Stores unique key-value pairs.Maintains insertion order.Allows one null key and multipl
7 min read
Hashtable in Java
The Hashtable class, introduced as part of the original Java Collections framework, implements a hash table that maps keys to values. Any non-null object can be used as a key or as a value. To successfully store and retrieve objects from a hashtable, the objects used as keys must implement the hashC
13 min read
Java Dictionary Class
Dictionary class in Java is an abstract class that represents a collection of key-value pairs, where keys are unique and used to access the values. It was part of the Java Collections Framework and it was introduced in Java 1.0 but has been largely replaced by the Map interface since Java 1.2. Store
5 min read
SortedSet Interface in Java with Examples
The SortedSet interface is present in java.util package extends the Set interface present in the collection framework. It is an interface that implements the mathematical set. This interface contains the methods inherited from the Set interface and adds a feature that stores all the elements in this
8 min read
Comparator Interface in Java with Examples
A comparator interface is used to order the objects of user-defined classes. A comparator object is capable of comparing two objects of the same class. Following function compare obj1 with obj2. Syntax: public int compare(Object obj1, Object obj2):Suppose we have an Array/ArrayList of our own class
6 min read
Java Comparable Interface
The Comparable interface in Java is used to define the natural ordering of objects for a user-defined class. It is part of the java.lang package and it provides a compareTo() method to compare instances of the class. A class has to implement a Comparable interface to define its natural ordering. Exa
4 min read
Java Comparable vs Comparator
In Java, both Comparable and Comparator are used for sorting objects. The main difference between Comparable and Comparator is: Comparable: It is used to define the natural ordering of the objects within the class.Comparator: It is used to define custom sorting logic externally.For a more thorough u
5 min read
Java Iterator
An Iterator in Java is an interface used to traverse elements in a Collection sequentially. It provides methods like hasNext(), next(), and remove() to loop through collections and perform manipulation. An Iterator is a part of the Java Collection Framework, and we can use it with collections like A
7 min read
Java Exception Handling
Exceptions in Java
Exception Handling in Java is one of the effective means to handle runtime errors so that the regular flow of the application can be preserved. Java Exception Handling is a mechanism to handle runtime errors such as ClassNotFoundException, IOException, SQLException, RemoteException, etc. What are Ja
10 min read
Checked vs Unchecked Exceptions in Java
In Java, Exception is an unwanted or unexpected event, which occurs during the execution of a program, i.e. at run time, that disrupts the normal flow of the program’s instructions. In Java, there are two types of exceptions: Checked exceptionsUnchecked exceptions Understanding the difference betwee
5 min read
Java Try Catch Block
In Java exception is an "unwanted or unexpected event", that occurs during the execution of the program. When an exception occurs, the execution of the program gets terminated. To avoid these termination conditions we can use try catch block in Java. In this article, we will learn about Try, catch,
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final, finally and finalize in Java
This is an important question concerning the interview point of view. final keyword final (lowercase) is a reserved keyword in java. We can't use it as an identifier, as it is reserved. We can use this keyword with variables, methods, and also with classes. The final keyword in java has a different
13 min read
throw and throws in Java
In Java, Exception Handling is one of the effective means to handle runtime errors so that the regular flow of the application can be preserved. Java Exception Handling is a mechanism to handle runtime errors such as NullPointerException, ArrayIndexOutOfBoundsException, etc. In this article, we will
4 min read
User-Defined Custom Exception in Java
In Java, an Exception is an issue (run time error) that occurred during the execution of a program. When an exception occurred the program gets terminated abruptly and, the code past the line that generated the exception never gets executed. Java provides us the facility to create our own exceptions
4 min read
Chained Exceptions in Java
Chained Exceptions in Java allow associating one exception with another, i.e. one exception describes the cause of another exception. For example, consider a situation in which a method throws an ArithmeticException because of an attempt to divide by zero, but the root cause of the error was an I/O
3 min read
Null Pointer Exception in Java
A NullPointerException in Java is a RuntimeException. In Java, a special null value can be assigned to an object reference. NullPointerException is thrown when a program attempts to use an object reference that has the null value. Example: [GFGTABS] Java // Demonstration of NullPointerException in J
5 min read
Exception Handling with Method Overriding in Java
An Exception is an unwanted or unexpected event, which occurs during the execution of a program i.e at run-time, that disrupts the normal flow of the program’s instructions. Exception handling is used to handle runtime errors. It helps to maintain the normal flow of the program. In any object-orient
6 min read
Java Multithreading
Java Multithreading Tutorial
Threads are the backbone of multithreading. We are living in a real world which in itself is caught on the web surrounded by lots of applications. With the advancement in technologies, we cannot achieve the speed required to run them simultaneously unless we introduce the concept of multi-tasking ef
15+ min read
Java Threads
Typically, we can define threads as a subprocess with lightweight with the smallest unit of processes and also has separate paths of execution. The main advantage of multiple threads is efficiency (allowing multiple things at the same time). For example, in MS Word. one thread automatically formats
9 min read
Java.lang.Thread Class in Java
Thread is a line of execution within a program. Each program can have multiple associated threads. Each thread has a priority which is used by the thread scheduler to determine which thread must run first. Java provides a thread class that has various method calls in order to manage the behavior of
8 min read
Runnable interface in Java
java.lang.Runnable is an interface that is to be implemented by a class whose instances are intended to be executed by a thread. There are two ways to start a new Thread - Subclass Thread and implement Runnable. There is no need of subclassing a Thread when a task can be done by overriding only run(
3 min read
Lifecycle and States of a Thread in Java
A thread in Java at any point of time exists in any one of the following states. A thread lies only in one of the shown states at any instant: New StateRunnable StateBlocked StateWaiting StateTimed Waiting StateTerminated StateThe diagram shown below represents various states of a thread at any inst
6 min read
Main thread in Java
Java provides built-in support for multithreaded programming. A multi-threaded program contains two or more parts that can run concurrently. Each part of such a program is called a thread, and each thread defines a separate path of execution.When a Java program starts up, one thread begins running i
4 min read
Java Thread Priority in Multithreading
As we already know java being completely object-oriented works within a multithreading environment in which thread scheduler assigns the processor to a thread based on the priority of thread. Whenever we create a thread in Java, it always has some priority assigned to it. Priority can either be give
5 min read
Naming a thread and fetching name of current thread in Java
Thread can be referred to as a lightweight process. Thread uses fewer resources to create and exist in the process; thread shares process resources. The main thread of Java is the thread that is started when the program starts. now let us discuss the eccentric concept of with what ways we can name a
5 min read
Difference between Thread.start() and Thread.run() in Java
In Java's multi-threading concept, start() and run() are the two most important methods. Below are some of the differences between the Thread.start() and Thread.run() methods: New Thread creation: When a program calls the start() method, a new thread is created and then the run() method is executed.
3 min read
Thread.sleep() Method in Java With Examples
Thread Class is a class that is basically a thread of execution of the programs. It is present in Java.lang package. Thread class contains the Sleep() method. There are two overloaded methods of Sleep() method present in Thread Class, one is with one argument and another one is with two arguments. T
4 min read
Daemon Thread in Java
In Java, daemon threads are low-priority threads that run in the background to perform tasks such as garbage collection or provide services to user threads. The life of a daemon thread depends on the mercy of user threads, meaning that when all user threads finish their execution, the Java Virtual M
4 min read
Thread Safety and how to achieve it in Java
As we know Java has a feature, Multithreading, which is a process of running multiple threads simultaneously. When multiple threads are working on the same data, and the value of our data is changing, that scenario is not thread-safe and we will get inconsistent results. When a thread is already wor
5 min read
Thread Pools in Java
Background Server Programs such as database and web servers repeatedly execute requests from multiple clients and these are oriented around processing a large number of short tasks. An approach for building a server application would be to create a new thread each time a request arrives and service
9 min read
Java File Handling
File Handling in Java
In Java, with the help of File Class, we can work with files. This File Class is inside the java.io package. The File class can be used by creating an object of the class and then specifying the name of the file. Why File Handling is Required? File Handling is an integral part of any programming lan
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Java.io.File Class in Java
Java File class is Java's representation of a file or directory pathname. Because file and directory names have different formats on different platforms, a simple string is not adequate to name them. Java File class contains several methods for working with the pathname, deleting and renaming files,
6 min read
Java Program to Create a New File
A File is an abstract path, it has no physical existence. It is only when "using" that File that the underlying physical storage is hit. When the file is getting created indirectly the abstract path is created. The file is one way, in which data will be stored as per requirement. Steps to Create a N
8 min read
Java Program to Write into a File
In this article, we will see different ways of writing into a File using Java Programming language. Java FileWriter class in java is used to write character-oriented data to a file as this class is character-oriented class because of what it is used in file handling in java. There are many ways to
7 min read
Delete a File Using Java
Java provides methods to delete files using java programs. On contrary to normal delete operations in any operating system, files being deleted using the java program are deleted permanently without being moved to the trash/recycle bin. Methods used to delete a file in Java: 1. Using java.io.File.de
2 min read
Java IO FileReader Class
FileReader in Java is a class in the java.io package which can be used to read a stream of characters from the files. Java IO FileReader class uses either specified charset or the platform's default charset for decoding from bytes to characters. 1. Charset: The Charset class is used to define method
3 min read
FileWriter Class in Java
Java FileWriter class of java.io package is used to write data in character form to file. Java FileWriter class is used to write character-oriented data to a file. It is a character-oriented class that is used for file handling in java. This class inherits from OutputStreamWriter class which in turn
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Java.io.FilePermission Class in Java
java.io.FilePermission class is used to represent access to a file or a directory. These accesses are in the form of a path name and a set of actions associated to the path name(specifies which file to be open along with the extension and the path). For Example, in FilePermission("GEEKS.txt", "read"
5 min read
Java.io.FileDescriptor in Java
java.io.FileDescriptor works for opening a file having a specific name. If there is any content present in that file it will first erase all that content and put "Beginning of Process" as the first line. Instances of the file descriptor class serve as an opaque handle to the underlying machine-speci
4 min read
Java Streams and Lambda Expressions
Java IO
Java IO : Input-output in Java with Examples
Java brings various Streams with its I/O package that helps the user to perform all the input-output operations. These streams support all the types of objects, data-types, characters, files etc to fully execute the I/O operations. Before exploring various input and output streams lets look at 3 sta
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Java.io.Reader class in Java
Java Reader class is an abstract class for reading character streams. The only methods that a subclass must implement are read(char[], int, int), and close(). Most subclasses, however, will override some of the methods defined here in order to provide higher efficiency, additional functionality, or
5 min read
Java.io.Writer Class in Java
java.io.Writer class is an abstract class. It is used to write to character streams. Declaration of Writer Class in Javapublic abstract class Writer extends Object implements Appendable, Closeable, FlushableConstructors of Java Writer Classprotected Writer(): Creates a new character stream that can
6 min read
Java.io.FileInputStream Class in Java
FileInputStream class is useful to read data from a file in the form of sequence of bytes. FileInputStream is meant for reading streams of raw bytes such as image data. For reading streams of characters, consider using FileReader. Constructors of FileInputStream Class 1. FileInputStream(File file):
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FileOutputStream in Java
FileOutputStream is an outputstream for writing data/streams of raw bytes to file or storing data to file. FileOutputStream is a subclass of OutputStream. To write primitive values into a file, we use FileOutputStream class. For writing byte-oriented and character-oriented data, we can use FileOutpu
5 min read
Ways to read input from console in Java
In Java, there are four different ways to read input from the user in the command line environment(console). 1. Using Buffered Reader ClassThis is the Java classical method to take input, Introduced in JDK 1.0. This method is used by wrapping the System.in (standard input stream) in an InputStreamRe
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Java.io.BufferedOutputStream class in Java
Java.io.BufferedInputStream class in Java Java.io.BufferedOutputStream class implements a buffered output stream. By setting up such an output stream, an application can write bytes to the underlying output stream without necessarily causing a call to the underlying system for each byte written. Fie
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Difference Between Scanner and BufferedReader Class in Java
In Java, Scanner and BufferedReader class are sources that serve as ways of reading inputs. Scanner class is a simple text scanner that can parse primitive types and strings. It internally uses regular expressions to read different types while on the other hand BufferedReader class reads text from a
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Fast I/O in Java in Competitive Programming
Using Java in competitive programming is not something many people would suggest just because of its slow input and output, and well indeed it is slow. In this article, we have discussed some ways to get around the difficulty and change the verdict from TLE to (in most cases) AC. Example: Input:7 31
7 min read
Java Networking
Java Networking
When computing devices such as laptops, desktops, servers, smartphones, and tablets and an eternally-expanding arrangement of IoT gadgets such as cameras, door locks, doorbells, refrigerators, audio/visual systems, thermostats, and various sensors are sharing information and data with each other is
15+ min read
TCP/IP Model
The TCP/IP model is a fundamental framework for computer networking. It stands for Transmission Control Protocol/Internet Protocol, which are the core protocols of the Internet. This model defines how data is transmitted over networks, ensuring reliable communication between devices. It consists of
14 min read
User Datagram Protocol (UDP)
User Datagram Protocol (UDP) is a Transport Layer protocol. UDP is a part of the Internet Protocol suite, referred to as UDP/IP suite. Unlike TCP, it is an unreliable and connectionless protocol. So, there is no need to establish a connection before data transfer. The UDP helps to establish low-late
10 min read
Difference Between IPv4 and IPv6
In the digital world, where billions of devices connect and communicate, Internet Protocol (IP) Addresses play a crucial role. These addresses are what allow devices to identify and locate each other on a network. To know all about IP Addresses - refer to What is an IP Address? Currently, there are
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Difference Between Connection-oriented and Connection-less Services
In computer networks, communication between devices occurs using two types of services: connection-oriented and connectionless. These services define how data is transferred between a source and a destination. Connection-oriented services establish a dedicated connection before data transfer, ensuri
5 min read
Socket Programming in Java
This article describes a very basic one-way Client and Server setup where a Client connects, sends messages to the server and the server shows them using a socket connection. There's a lot of low-level stuff that needs to happen for these things to work but the Java API networking package (java.net)
5 min read
java.net.ServerSocket Class in Java
ServerSocket Class is used for providing system-independent implementation of the server-side of a client/server Socket Connection. The constructor for ServerSocket throws an exception if it can't listen on the specified port (for example, the port is already being used). It is widely used so the ap
4 min read
URL Class in Java with Examples
URL known as Uniform Resource Locator is simply a string of text that identifies all the resources on the Internet, telling us the address of the resource, how to communicate with it, and retrieve something from it. Components of a URL A URL can have many forms. The most general however follows a th
4 min read
Java Memory Allocation
Java Memory Management
This article will focus on Java memory management, how the heap works, reference types, garbage collection, and also related concepts. Why Learn Java Memory Management? We all know that Java itself manages the memory and needs no explicit intervention of the programmer. Garbage collector itself ensu
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How are Java objects stored in memory?
In Java, all objects are dynamically allocated on Heap. This is different from C++ where objects can be allocated memory either on Stack or on Heap. In JAVA , when we allocate the object using new(), the object is allocated on Heap, otherwise on Stack if not global or static.In Java, when we only de
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Stack vs Heap Memory Allocation
Memory in a C/C++/Java program can either be allocated on a stack or a heap.Prerequisite: Memory layout of C program. Stack Allocation: The allocation happens on contiguous blocks of memory. We call it a stack memory allocation because the allocation happens in the function call stack. The size of m
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Java Virtual Machine (JVM) Stack Area
For every thread, JVM creates a separate stack at the time of thread creation. The memory for a Java Virtual Machine stack does not need to be contiguous. The Java virtual machine only performs two operations directly on Java stacks: it pushes and pops frames. And stack for a particular thread may b
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How many types of memory areas are allocated by JVM?
JVM (Java Virtual Machine) is an abstract machine, In other words, it is a program/software which takes Java bytecode and converts the byte code (line by line) into machine understandable code. JVM(Java Virtual Machine) acts as a run-time engine to run Java applications. JVM is the one that actuall
3 min read
Garbage Collection in Java
Garbage collection in Java is the process by which Java programs perform automatic memory management. Java programs compile to bytecode that can be run on a Java Virtual Machine, or JVM for short. When Java programs run on the JVM, objects are created on the heap, which is a portion of memory dedica
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Types of JVM Garbage Collectors in Java with implementation details
prerequisites: Garbage Collection, Mark and Sweep algorithm Garbage Collection: Garbage collection aka GC is one of the most important features of Java. Garbage collection is the mechanism used in Java to de-allocate unused memory, which is nothing but clear the space consumed by unused objects. To
5 min read
Stack vs Heap Memory Allocation
Memory in a C/C++/Java program can either be allocated on a stack or a heap.Prerequisite: Memory layout of C program. Stack Allocation: The allocation happens on contiguous blocks of memory. We call it a stack memory allocation because the allocation happens in the function call stack. The size of m
7 min read
Memory leaks in Java
In C, programmers totally control allocation and deallocation of dynamically created objects. And if a programmer does not destroy objects, memory leak happens in C, Java does automatic Garbage collection. However there can be situations where garbage collector does not collect objects because there
1 min read
Java Interview Questions
Java Interview Questions and Answers
Java is one of the most popular programming languages in the world, known for its versatility, portability, and wide range of applications. Java is the most used language in top companies such as Uber, Airbnb, Google, Netflix, Instagram, Spotify, Amazon, and many more because of its features and per
15+ min read
Java Multiple Choice Questions
Java is a widely used high-level, general-purpose, object-oriented programming language and platform that was developed by James Gosling in 1982. Java Supports WORA(Write Once, Run Anywhere) also, it defined as 7th most popular programming language in the world. Java language is a high-level, multi-
3 min read
Java Projects
Top 50 Java Project Ideas For Beginners and Advanced [Update 2025]
Java is one of the most popular and versatile programming languages, known for its reliability, security, and platform independence. Developed by James Gosling in 1982, Java is widely used across industries like big data, mobile development, finance, and e-commerce. Building Java projects is an exce
15+ min read
Number guessing game in Java
The task is to write a Java program in which a user will get K trials to guess a randomly generated number. Below are the rules of the game: If the guessed number is bigger than the actual number, the program will respond with the message that the guessed number is higher than the actual number.If t
3 min read
Mini Banking Application in Java
In any Bank Transaction, there are several parties involved to process transaction like a merchant, bank, receiver, etc. so there are several numbers reasons that transaction may get failed, declined, so to handle a transaction in Java, there is a JDBC (Java Database Connectivity) which provides us
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Java program to convert Currency using AWT
Swing is a part of the JFC (Java Foundation Classes). Building Graphical User Interface in Java requires the use of Swings. Swing Framework contains a large set of components which allow a high level of customization and provide rich functionalities, and is used to create window-based applications.
4 min read
Tic-Tac-Toe Game in Java
In the Tic-Tac-Toe game, you will see the approach of the game is implemented. In this game, two players will be played and you have one print board on the screen where from 1 to 9 number will be displayed or you can say it box number. Now, you have to choose X or O for the specific box number. For
6 min read
Design Snake Game
Let us see how to design a basic Snake Game that provides the following functionalities: Snake can move in a given direction and when it eats the food, the length of snake increases. When the snake crosses itself, the game will be over. Food will be generated at a given interval.Asked In: Amazon, Mi
9 min read
Memory Game in Java
The Memory Game is a game where the player has to flip over pairs of cards with the same symbol. We create two arrays to represent the game board: board and flipped. The board is an array of strings that represents the state of the game board at any given time.When a player flips a card, we replace
3 min read
How to Implement a Simple Chat Application Using Sockets in Java?
In this article, we will create a simple chat application using Java socket programming. Before we are going to discuss our topic, we must know Socket in Java. Java Socket connects two different JREs (Java Runtime Environment). Java sockets can be connection-oriented or connection-less. In Java, we
4 min read
Image Processing in Java - Face Detection
Prerequisites: Image Processing in Java - Read and WriteImage Processing In Java - Get and Set PixelsImage Processing in Java - Colored Image to Grayscale Image ConversionImage Processing in Java - Colored Image to Negative Image ConversionImage Processing in Java - Colored to Red Green Blue Image C
3 min read
Design Media Sharing Social Networking System
PURPOSE OF MEDIA SOCIAL NETWORKING SERVICE SYSTEMThis system will allow users to share photos and videos with other users. Additionally, users can follow other users based on follow request and they can see other user's photos and videos. In this system, you can search users and see their profile if
14 min read
Java Swing | Create a simple text editor
To create a simple text editor in Java Swing we will use a JTextArea, a JMenuBar and add JMenu to it and we will add JMenuItems. All the menu items will have actionListener to detect any action.There will be a menu bar and it will contain two menus and a button: File menuopen: this menuitem is used
6 min read
