Main thread in Java
Last Updated :
21 Sep, 2021
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 immediately. This is usually called the main thread of our program because it is the one that is executed when our program begins.
There are certain properties associated with the main thread which are as follows:
- It is the thread from which other “child” threads will be spawned.
- Often, it must be the last thread to finish execution because it performs various shutdown actions
The flow diagram is as follows:
How to control Main thread
The main thread is created automatically when our program is started. To control it we must obtain a reference to it. This can be done by calling the method currentThread( ) which is present in Thread class. This method returns a reference to the thread on which it is called. The default priority of Main thread is 5 and for all remaining user threads priority will be inherited from parent to child.
Example
Java
import java.io.*;
import java.util.*;
public class Test extends Thread {
public static void main(String[] args)
{
Thread t = Thread.currentThread();
System.out.println("Current thread: "
+ t.getName());
t.setName("Geeks");
System.out.println("After name change: "
+ t.getName());
System.out.println("Main thread priority: "
+ t.getPriority());
t.setPriority(MAX_PRIORITY);
System.out.println("Main thread new priority: "
+ t.getPriority());
for (int i = 0; i < 5; i++) {
System.out.println("Main thread");
}
Thread ct = new Thread() {
public void run()
{
for (int i = 0; i < 5; i++) {
System.out.println("Child thread");
}
}
};
System.out.println("Child thread priority: "
+ ct.getPriority());
ct.setPriority(MIN_PRIORITY);
System.out.println("Child thread new priority: "
+ ct.getPriority());
ct.start();
}
}
class ChildThread extends Thread {
@Override public void run()
{
for (int i = 0; i < 5; i++) {
System.out.println("Child thread");
}
}
}
|
Output
Current thread: main
After name change: Geeks
Main thread priority: 5
Main thread new priority: 10
Main thread
Main thread
Main thread
Main thread
Main thread
Child thread priority: 10
Child thread new priority: 1
Child thread
Child thread
Child thread
Child thread
Child thread
Now let us discuss the relationship between the main() method and the main thread in Java. For each program, a Main thread is created by JVM(Java Virtual Machine). The “Main” thread first verifies the existence of the main() method, and then it initializes the class. Note that from JDK 6, main() method is mandatory in a standalone java application.
Deadlocking with use of Main Thread(only single thread)
We can create a deadlock by just using the Main thread, i.e. by just using a single thread.
Example
Java
public class GFG {
public static void main(String[] args) {
try {
System.out.println("Entering into Deadlock");
Thread.currentThread().join();
System.out.println("This statement will never execute");
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
}
|
Output:
Output explanation:
The statement “Thread.currentThread().join()”, will tell Main thread to wait for this thread(i.e. wait for itself) to die. Thus Main thread wait for itself to die, which is nothing but a deadlock.
Related Article: Daemon Threads in Java.
Please Login to comment...
