Java Thread join() method

The join() method of thread class waits for a thread to die. It is used when you want one thread to wait for completion of another. This process is like a relay race where the second runner waits until the first runner comes and hand over the flag to him.

Syntax

public final void join()throws InterruptedException
public void join(long millis)throwsInterruptedException
public final void join(long millis, int nanos)throws InterruptedException

Parameter

millis: It defines the time to wait in milliseconds
nanos: 0-999999 additional nanoseconds to wait

Return

Exception

IllegalArgumentException: This exception throws if the value of millis is negative, or the value of nanos is not in the range 0-999999

InterruptedException: This exception throws if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

Example 1

public class JoinExample1 extends Thread
{  
    public void run()
    {  
        for(int i=1; i<=4; i++)
        {  
            try
            {  
                Thread.sleep(500);  
            }catch(Exception e){System.out.println(e);}  
            System.out.println(i);  
        }  
    }  
    public static void main(String args[])
    { 
        // creating three threads
        JoinExample1 t1 = new JoinExample1();  
        JoinExample1 t2 = new JoinExample1();  
        JoinExample1 t3 = new JoinExample1();  
        // thread t1 starts
        t1.start(); 
        // starts second thread when first thread t1 is died.
        try
        {  
            t1.join();  
        }catch(Exception e){System.out.println(e);}  
        // start t2 and t3 thread 
        t2.start(); 
        t3.start();  
    }  
}

Test it Now

Output:

In the above example 1, when t1 completes its task then t2 and t3 starts execution.

Example 2

public class JoinExample2 extends Thread
{  
    public void run()
    {  
        for(int i=1; i<=5; i++)
        {  
            try
            {  
                Thread.sleep(500);  
            }catch(Exception e){System.out.println(e);}  
            System.out.println(i);  
        }  
    }  
    public static void main(String args[])
    {  
        // creating three threads
        JoinExample2 t1 = new JoinExample2();  
        JoinExample2 t2 = new JoinExample2();  
        JoinExample2 t3 = new JoinExample2();  
        // thread t1 starts
        t1.start();
        // starts second thread when first thread t1 is died.
        try
        {  
            t1.join(1500);  
        }catch(Exception e){System.out.println(e);}  
        // start t2 and t3 thread 
        t2.start(); 
        t3.start();  
    }  
}

Test it Now

Output: