Problem in understanding join()

[Arpit Gadle]

Hi,
I am preparing for SCJP 6.0. I am having a problem in understanding join() method.
Can any body provide a small program demonstrating use of join().

[Henry Wong]

Arpit Gadle wrote:Hi,
I am preparing for SCJP 6.0. I am having a problem in understanding join() method.
Can any body provide a small program demonstrating use of join().

The join() method is used to wait for another thread to finish. So, when you call the join() method on a thread object, the method will not return, until the thread represented by the thread object has finished.

I am not sure what "problem in understanding" that you may be having. Or how could an example program can really help more than what I just described. Perhaps you can elaborate the issue that you are having.

Henry

[Arpit Gadle]

I am clear with the definition. But was having problem in writing small example which demonstrates how join() actually works. After posting this topic, I tried for a while and wrote a program which actually shows how join() works

class Job_1
	implements Runnable
{
	public void run()	
       {
		for(int x='z';x>='a';x--)		
			System.out.println("\t\t\t"+Thread.currentThread().getName()+"-->"+(char)x);
       }
}

class Job_2
	implements Runnable
{
	public void run()
	{
		for(int x=1;x<=26;x++)
			System.out.println(Thread.currentThread().getName()+"-->"+x);
	}	
}
class Job_3
	implements Runnable
{
	public void run()
	{
		for(int x='!';x>='!'-26;x--)
			System.out.println("\t\t\t"+Thread.currentThread().getName()+"-->"+(char)x);
	}
}
public class MultiJobs_n_Threads
{
	public static void main(String [] args)
	{
		Job_1 job_1=new Job_1();
		Job_2 job_2=new Job_2();
		Job_3 job_3=new Job_3();
		
		Thread t1=new Thread(job_1);
		Thread t2=new Thread(job_2);
		Thread t3=new Thread(job_3);
			
		t1.setName("Job_1");
		t1.start();

		t2.setName("Job_2");
		t2.start();

		t3.setName("Job_3");
		t3.start();

		try
		{
			t2.join();
		}
		catch(InterruptedException ie)	{	}

		System.out.println("Exiting main()...");
	}
}

What this code does is, it joins the current thread (main) to thread t2. So the current thread will not become runnable until t2 has finihsed.

Where should I place call to join() so that thread t2 can join thread t3.

[Paul Clapham]

You want the thread which runs the Job_2 class to wait at some point during that running for t3 to terminate before continuing? Then you would call t3.join() in the Job_2 class.