threads

[sri vidya]

Hi,
Please tell me how one thread can start another thread. If possible please give an example.

thanks,
Srividya.

[deekasha gunwant]

Hi srividya,
I've written small code for u hope ithelps you.

import java.io.*;
class ChildThread implements Runnable
{
  int id ;
  ChildThread(int j)
  {
    id = j;
  }
  public void run()
  {
    System.out.println("Started running my id is "+id);
    for(int i=0;i<id;i++)>
    {
System.out.println("Child No. : "+id + " Welcomes you Sri Vidya");
}
  }
}

class ParentThread implements Runnable
{
  int childNum ;
  ParentThread(int num)
  {
     System.out.println("Hi SriVidya I'm ParentThread just got life");
     System.out.println("I'll be creating 5 threads just keep on watching.");
     childNum = num;
  }
  public void run()
  {
     for(int i=1;i<=childNum;i++)
     {
       System.out.println("Creating ChildThread # "+i);
       Thread t = new Thread(new ChildThread(i));
       t.start();
       System.out.println("Started ChildThread # "+i);
     }
  }
}
class ThreadFromThread
{
  public static void main(String args[])
  {
     Thread  pt = new Thread(new ParentThread(5));
     System.out.println("press enter to start");
     try
     {
        System.in.read();
     }
     catch(IOException ie)
     {
 ie.printStackTrace();
 }
     System.out.println("Starting ParentThread");
     pt.start();
  }
}

do get back in case of any doubt
regards
deekasha

[This message has been edited by deekasha gunwant (edited October 12, 2000).]

[Ajith Kallambella]

Yes ofcourse. Any thread is just a piece of code which is run asynchronously. So whatever you are allowed to do in a normal program, you can do the same in the body of the thread also.
Infact, the main method itself is a thread and so any threads started by the main method is a classic example of one thread spawining another one.
Here is a small program I wrote to demonstrate this concept. Since the program is well documented, I will let you explore it. Note how the threads are created.
Thread1( Devil-1 ) --> Creates Thread2( Devil-2 )
Thread2( Devil-2 ) --> Creates Thread3( Devil-3 ) and so on till the room is full of Devils!!.... don't get scared

public class MultiThreads  extends Thread
{
    public static final int  MAX_THREADS        = 5 ;
    public static int        nActiveCount       = 0 ;
    // We will use this thread group and create new threads under this group.
    // Hence it is static and final  [img]http://www.javaranch.com/ubb/smile.gif[/img]
    public static final ThreadGroup BlueDevils = new ThreadGroup("BlueDevils");
    MultiThreads()
    {
        // Create a new thread under the BlueDevils thread group.
        // Also assign an id to the new thread .
        super( BlueDevils, "Devil-"+ ++nActiveCount  );  // ThreadGroup, String format
    }
    
    public static void main( String[] s)
    {
        // The 'grand mother' thread
        new MultiThreads().start();
    }
    
    public void run()
    {
        System.out.println( "ThreadGroup   : " + getThreadGroup().getName());
        System.out.println( "Thread Name   : " + getName());
        //System.out.println( "Parent Thread : " + 
        System.out.println( "Creating the next thread....") ;
        System.out.println( );
        
        // If still under the max limit, create the next thread..
        if ( nActiveCount < MAX_THREADS )
            new MultiThreads().start();
        else
            System.out.println("Can't create any more devils... the room is full. See ya!!");            
    }
}

Hope this helps. Let me know if you still have any questions !!
Ajith

[Ajith Kallambella]

Oops!!.. Looks like me and deekasha were trying to answer your question in a non-synchronized manner. This is what happens by the way if you don't get a lock on the object first
Great code deekasha!!
Ajith