Java.lang.ThreadGroup class in Java

ThreadGroup creates a group of threads. It offers a convenient way to manage groups of threads as a unit. This is particularly valuable in situation in which you want to suspend and resume a number of related threads.

The thread group form a tree in which every thread group except the initial thread group has a parent.
A thread is allowed to access information about its own thread group but not to access information about its thread group’s parent thread group or any other thread group.

Constructors:

public ThreadGroup(String name): Constructs a new thread group. The parent of this new group is the thread group of the currently running thread.
```
Throws: SecurityException - if the current thread cannot
 create a thread in the specified thread group.
```

public ThreadGroup(ThreadGroup parent, String name): Creates a new thread group. The parent of this new group is the specified thread group.

Throws: 
NullPointerException - if the thread group argument is null.
SecurityException - if the current thread cannot create a thread in the 
specified thread group.

Methods

int activeCount(): This method returns the number of threads in the group plus any group for which this thread is parent.

Syntax: public int activeCount()
Returns: This method returns an estimate of the number of 
active threads in this thread group and in any other thread group 
that has this thread group as an ancestor.
Exception: NA

// Java code illustrating activeCount() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 1000; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
                System.out.println("Exception encounterted"); 
            } 
        } 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("parent thread group"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting one"); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting two"); 
  
        // checking the number of active thread 
        System.out.println("number of active thread: "
                           + gfg.activeCount()); 
    } 
} 

Output:

Starting one
Starting two
number of active thread: 2

int activeGroupCount(): This method returns an estimate of the number of active groups in this thread group.

Syntax: public int activeGroupCount().
Returns: Returns the number of groups for which the invoking thread is parent.
Exception: NA.

// Java code illustrating activeGroupCount() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 1000; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
                System.out.println("Exception encounterted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() +  
            " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("gfg"); 
  
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting one"); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting two"); 
  
        // checking the number of active thread 
        System.out.println("number of active thread group: "
                           + gfg.activeGroupCount()); 
    } 
} 

Output:

Starting one
Starting two
number of active thread group: 2
one finished executing
two finished executing

void checkAccess(): Causes the security manager to verify that the invoking thread may access and/ or change the group on which checkAccess() is called.

Syntax: final void checkAccess().
Returns: NA.
Exception: NA.

// Java code illustrating checkAccess() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 1000; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
                System.out.println("Exception encounterted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() + 
              " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
  
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting one"); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting two"); 
        gfg.checkAccess(); 
        System.out.println(gfg.getName() + " has access"); 
        gfg_child.checkAccess(); 
        System.out.println(gfg_child.getName() + " has access"); 
    } 
} 

Output:

Starting one
Starting two
Parent thread has access
child thread has access
one finished executing 
two finished executing

void destroy(): Destroys the thread group and any child groups on which it is called.

Syntax: public void destroy().
Returns: NA.
Exception: 
IllegalThreadStateException - if the thread group is not 
empty or if the thread group has already been destroyed.
SecurityException - if the current thread cannot modify this thread group.

// Java code illustrating destroy() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
                System.out.println("Exception encounterted"); 
            } 
        } 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
  
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting one"); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting two"); 
  
        // block until other thread is finished 
        t1.join(); 
        t2.join(); 
  
        // destroying child thread 
        gfg_child.destroy(); 
        System.out.println(gfg_child.getName() + " destroyed"); 
  
        // destroying parent thread 
        gfg.destroy(); 
        System.out.println(gfg.getName() + " destroyed"); 
    } 
} 

Output:

Starting one
Starting two
child thread destroyed
Parent thread destroyed

int enumerate(Thread group[]): The thread that comprise the invoking thread group are put into the group array.

Syntax: public int enumerate(Thread group[]).
Returns: the number of threads put into the array.
Exception: SecurityException - if the current thread 
does not have permission to enumerate this thread group.

// Java code illustrating enumerate() method. 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex) { 
                System.out.println("Exception encounterted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() + 
             " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
  
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting one"); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting two"); 
  
        // returns the number of threads put into the array 
        Thread[] group = new Thread[gfg.activeCount()]; 
        int count = gfg.enumerate(group); 
        for (int i = 0; i < count; i++)  
        { 
            System.out.println("Thread " + group[i].getName() + " found"); 
        } 
    } 
} 

Output:

Starting one
Starting two
Thread one found
Thread two found
one finished executing
two finished executing

int enumerate(Thread[] group, boolean recurse): The threads that comprise the invoking thread group are put into the group array. If all is true, then threads in all subgroups of the thread are also put into group.

Syntax: public int enumerate(Thread[] list, boolean recurse).
Returns: the number of threads placed into the array.
Exception: SecurityException - if the current thread does 
not have permission to enumerate this thread group.

// Java code illustrating enumerate(Thread[] group, boolean recurse) 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
                System.out.println("Exception encounterted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() + 
              " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
  
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting one"); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting two"); 
  
        // returns the number of threads put into the array 
        Thread[] group = new Thread[gfg.activeCount()]; 
        int count = gfg.enumerate(group, true); 
        for (int i = 0; i < count; i++)  
        { 
            System.out.println("Thread " + group[i].getName() + " found"); 
        } 
    } 
} 

Output:

Starting one
Starting two
Thread one found
Thread two found
one finished executing
two finished executing

int enumerate(ThreadGroup[] group): The subgroups of the evoking thread group are put into the group array.

Syntax: public int enumerate(ThreadGroup[] group).
Returns: the number of thread groups put into the array.
Exception: SecurityException - if the current thread does 
not have permission to enumerate this thread group.

// Java code illustrating enumerate(ThreadGroup[] group) method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
                System.out.println("Exception encounterted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() +  
               " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
  
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting one"); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting two"); 
  
        // returns the number of threads put into the array 
        ThreadGroup[] group = new ThreadGroup[gfg.activeCount()]; 
        int count = gfg.enumerate(group); 
        for (int i = 0; i < count; i++)  
        { 
            System.out.println("ThreadGroup " + group[i].getName() + 
                " found"); 
        } 
    } 
} 

Output:

Starting one
Starting two
ThreadGroup child thread found
two finished executing
one finished executing

int enumerate(ThreadGroup[] group, boolean all): The subgroups of the invoking thread group are put into the group array. If all is true, then all subgroups of the subgroups(and so on) are also put into group.

Syntax: public int enumerate(ThreadGroup[] group, boolean all)
Returns: the number of thread groups put into the array.
Exception: SecurityException - if the current thread does 
not have permission to enumerate this thread group.

// Java code illustrating enumerate(ThreadGroup[] group, boolean all) 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
                System.out.println("Exception encounterted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() + 
               " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
  
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting one"); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting two"); 
  
        // returns the number of threads put into the array 
        ThreadGroup[] group = new ThreadGroup[gfg.activeCount()]; 
        int count = gfg.enumerate(group, true); 
        for (int i = 0; i < count; i++)  
        { 
            System.out.println("ThreadGroup " + group[i].getName() +  
                " found"); 
        } 
    } 
} 

Output:

Starting one
Starting two
ThreadGroup child thread found
two finished executing
one finished executing

int getMaxPriority(): Returns the maximum priority setting for the group.

Syntax: final int getMaxPriority().
Returns: the maximum priority that a thread in this thread group can have.
Exception: NA.

// Java code illustrating getMaxPriority() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
                System.out.println("Exception encounterted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() + 
               " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        // checking the maximum priority of parent thread 
        System.out.println("Maximum priority of ParentThreadGroup = "
                           + gfg.getMaxPriority()); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting one"); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting two"); 
    } 
} 

Output:

Maximum priority of ParentThreadGroup = 10
Starting one
Starting two
two finished executing
one finished executing

String getName(): This method returns the name of the group.

Syntax: final String getName().
Returns: the name of this thread group.
Exception: NA.

// Java code illustrating getName() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
                System.out.println("Exception encounterted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() +  
             " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting " + t1.getName()); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting " + t2.getName()); 
    } 
} 

Output:

Starting one
Starting two
two finished executing
one finished executing

ThreadGroup getParent(): Returns null if the invoking ThreadGroup object has no parent. Otherwise, it returns the parent of the invoking object.

Syntax: final ThreadGroup getParent().
Returns: the parent of this thread group. 
The top-level thread group is the only thread group 
whose parent is null.
Exception: SecurityException - if the current thread 
cannot modify this thread group.

// Java code illustrating getParent() method 
import java.lang.*; 
class NewThread extends Thread { 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++) { 
            try { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex) { 
                System.out.println("Exception encounterted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() 
                                            + " finished executing"); 
    } 
} public class ThreadGroupDemo { 
public static void main(String arg[]) throws InterruptedException, 
        SecurityException 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting " + t1.getName()); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting " + t2.getName()); 
  
        // prints the parent ThreadGroup  
        // of both parent and child threads 
        System.out.println("ParentThreadGroup for " + gfg.getName() + 
                        " is " + gfg.getParent().getName()); 
        System.out.println("ParentThreadGroup for " + gfg_child.getName()  
                        + " is " + gfg_child.getParent().getName()); 
    } 
} 

Output:

Starting one
Starting two
ParentThreadGroup for Parent thread is main
ParentThreadGroup for child thread is Parent thread
one finished executing
two finished executing

void interrupt(): Invokes the interrupt() methods of all threads in the group.

Syntax: public final void interrupt().
Returns: NA.
Exception: SecurityException - if the current thread is not 
allowed to access this thread group or any of the threads in the thread group.

// Java code illustrating interrupt() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
              System.out.println("Thread " + Thread.currentThread().getName() 
                                   + " interrupted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() +  
             " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting " + t1.getName()); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting " + t2.getName()); 
  
        // interrupting thread group 
        gfg.interrupt(); 
    } 
} 

Output:

Starting one
Starting two
Thread two interrupted
Thread one interrupted
one finished executing
two finished executing

boolean isDaemon(): Tests if this thread group is a daemon thread group. A daemon thread group is automatically destroyed when its last thread is stopped or its last thread group is destroyed.

Syntax: public final boolean isDaemon().
Returns: true if the group is daemon group. Otherwise it returns false.
Exception: NA.

// Java code illustrating isDaemon() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
              System.out.println("Thread " + Thread.currentThread().getName() 
                                   + " interrupted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() +  
                " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting " + t1.getName()); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting " + t2.getName()); 
  
        if (gfg.isDaemon() == true) 
            System.out.println("Group is Daemon group"); 
        else
            System.out.println("Group is not Daemon group"); 
    } 
} 

Output:

Starting one
Starting two
Group is not Daemon group
two finished executing
one finished executing

boolean isDestroyed(): This method tests if this thread group has been destroyed.

Syntax: public boolean isDestroyed().
Returns: true if this object is destroyed.
Exception: NA.

// Java code illustrating isDestroyed() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
              System.out.println("Thread " + Thread.currentThread().getName() 
                                   + " interrupted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() +  
                " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException, Exception 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting " + t1.getName()); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting " + t2.getName()); 
  
        if (gfg.isDestroyed() == true) 
            System.out.println("Group is destroyed"); 
        else
            System.out.println("Group is not destroyed"); 
    } 
} 

Output:

Starting one
Starting two
Group is not destroyed
one finished executing
two finished executing

void list(): Displays information about the group.

Syntax: public void list().
Returns: NA.
Exception: NA.

// Java code illustrating list() method. 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
              System.out.println("Thread " + Thread.currentThread().getName() 
                                   + " interrupted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() +  
              " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException, Exception 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting " + t1.getName()); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting " + t2.getName()); 
  
        // listing contents of parent ThreadGroup 
        System.out.println("\nListing parentThreadGroup: " + gfg.getName()  
              + ":"); 
        // prints information about this thread group 
        // to the standard output 
        gfg.list(); 
    } 
} 

Output:

Starting one
Starting two

Listing parentThreadGroup: Parent thread:
java.lang.ThreadGroup[name=Parent thread, maxpri=10]
    Thread[one, 5, Parent thread]
    Thread[two, 5, Parent thread]
    java.lang.ThreadGroup[name=child thread, maxpri=10]
one finished executing
two finished executing

boolean parentOf(ThreadGroup group): This method tests if this thread group is either the thread group argument or one of its ancestor thread groups.

Syntax: final boolean parentOf(ThreadGroup group).
Returns: true if the invoking thread is the parent 
of group(or group itself). Otherwise, it returns false.
Exception: NA.

// Java code illustrating parentOf() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
              System.out.println("Thread " + Thread.currentThread().getName() 
                                   + " interrupted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() +  
                " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException, Exception 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting " + t1.getName()); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting " + t2.getName()); 
  
        // checking who is parent thread 
        if (gfg.parentOf(gfg_child)) 
            System.out.println(gfg.getName() + " is parent of " + 
               gfg_child.getName()); 
    } 
} 

Output:

Starting one
Starting two
Parent thread is parent of child thread
two finished executing
one finished executing

void setDaemon(boolean isDaemon): This method changes the daemon status of this thread group. A daemon thread group is automatically destroyed when its last thread is stopped or its last thread group is destroyed.

Syntax: final void setDaemon(boolean isDaemon).
Returns: If isDaemon is true, then the invoking group is 
flagged as a daemon group.
Exception: SecurityException - if the current 
thread cannot modify this thread group.

// Java code illustrating setDaemon() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
              System.out.println("Thread " + Thread.currentThread().getName() 
                                   + " interrupted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() +  
               " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException, Exception 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        // daemon status is set to true 
        gfg.setDaemon(true); 
  
        // daemon status is set to true 
        gfg_child.setDaemon(true); 
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting " + t1.getName()); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting " + t2.getName()); 
  
        if (gfg.isDaemon() && gfg_child.isDaemon()) 
            System.out.println("Parent Thread group and "
                               + "child thread group"
                               + " is daemon"); 
    } 
} 

Output:

Starting one
Starting two
Parent Thread group and child thread group is daemon
one finished executing
two finished executing

void setMaxPriority(int priority): Sets the maximum priority of the invoking group to priority.

Syntax: final void setMaxPriority(int priority).
Returns: NA.
Exception: SecurityException - if the current thread 
cannot 
modify this thread group.

// Java code illustrating setMaxPriority() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
              System.out.println("Thread " + Thread.currentThread().getName() 
                                   + " interrupted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() +  
                 " [priority = " +  
           Thread.currentThread().getPriority() + "] 
                finished executing."); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException, Exception 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
        gfg.setMaxPriority(Thread.MAX_PRIORITY - 2); 
        gfg_child.setMaxPriority(Thread.NORM_PRIORITY); 
  
        NewThread t1 = new NewThread("one", gfg); 
        t1.setPriority(Thread.MAX_PRIORITY); 
        System.out.println("Starting " + t1.getName()); 
        t1.start(); 
        NewThread t2 = new NewThread("two", gfg_child); 
        t2.setPriority(Thread.MAX_PRIORITY); 
        System.out.println("Starting " + t2.getName()); 
        t2.start(); 
    } 
} 

Output:

Starting one
Starting two
two [priority = 5] finished executing.
one [priority = 8] finished executing.

String toString(): This method returns a string representation of this Thread group.

Syntax: public String toString().
Returns: String equivalent of the group.
Exception: SecurityException - if the current thread 
cannot modify this thread group.

// Java code illustrating toString() method 
import java.lang.*; 
class NewThread extends Thread  
{ 
    NewThread(String threadname, ThreadGroup tgob) 
    { 
        super(tgob, threadname); 
        start(); 
    } 
public void run() 
    { 
  
        for (int i = 0; i < 10; i++)  
        { 
            try 
            { 
                Thread.sleep(10); 
            } 
            catch (InterruptedException ex)  
            { 
              System.out.println("Thread " + Thread.currentThread().getName() 
                                   + " interrupted"); 
            } 
        } 
        System.out.println(Thread.currentThread().getName() +  
              " finished executing"); 
    } 
}  
public class ThreadGroupDemo  
{ 
    public static void main(String arg[]) throws InterruptedException, 
        SecurityException, Exception 
    { 
        // creating the thread group 
        ThreadGroup gfg = new ThreadGroup("Parent thread"); 
        ThreadGroup gfg_child = new ThreadGroup(gfg, "child thread"); 
  
        // daemon status is set to true 
        gfg.setDaemon(true); 
  
        // daemon status is set to true 
        gfg_child.setDaemon(true); 
        NewThread t1 = new NewThread("one", gfg); 
        System.out.println("Starting " + t1.getName()); 
        NewThread t2 = new NewThread("two", gfg); 
        System.out.println("Starting " + t2.getName()); 
  
        // string equivalent of the parent group 
        System.out.println("String equivalent: " + gfg.toString()); 
    } 
} 

Output:

Starting one
Starting two
String equivalent: java.lang.ThreadGroup[name=Parent thread, maxpri=10]
one finished executing
two finished executing

This article is contributed by Abhishek Verma. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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