Need practical example of wait() and notify()

[Kay Crocker]

I have been looking up information about threads and I am a little confused about wait() and notify(). Actually, I am trying to think of a practical situation where you would want to use these function calls.
Can anyone help?

[Mo Ibrahim]

Here you go Kay

public class OneThread extends Thread
{
    private String name;
    private static int[] flag = new int[1];
    private static boolean go;
    
    public OneThread(String theName)
    {
        name = theName;
    }
    
    public void run()
    {
        synchronized(flag) {
            System.out.println("Inside Synch " + name);
            while (!go) {
                try {
                    System.out.println("Before wait " + name);
                    flag.wait();
                    System.out.println("After wait " + name);
                }catch (InterruptedException ie)
                {}
            }
            System.out.println("Name is " + name);
            flag.notifyAll();
            System.out.println("After notifyAll " + name);
        }
    }
    
    public void setGo(boolean bool)
    {
        go = bool;
    }
    
    public static void main(String[] args)
    {
        OneThread thread1 = new OneThread("one");
        OneThread thread2 = new OneThread("two");
        thread1.start();
        thread2.start();
        try{
            Thread.sleep(1000);
        }
        catch (InterruptedException ie) {}        
        thread2.setGo(true);
        OneThread thread3 = new OneThread("three");
        thread3.start();
    }
}

i have put the sleep in the main() just to let you see what's going on.
After the program has run, you can see the sequence of events happening, how the first two threads are waiting while the third one has completes and lets the other threads run.

[netharam ram]

Here is another simpler example for wait() notify().
code:
**********************************************
// Without using Synchronization, with priority.
class Stwait implements Runnable
{
String s1="null",s2;
int flag=2;
Stwait()
{
Thread t2=new Thread(this,"two");
t2.start();
t2.setPriority(8);
Thread t3=new Thread(this,"three");
t3.start();
t3.setPriority(6);
}
public void run()
{
synchronized(this)
{
for (int i=0;i<3;i++)
{
s2=Thread.currentThread().getName();

if(s2.equals("one"))
{if (flag==1)
{ flag=1;
System.out.println(s2 +" Waiting ");
s1=s2;
try{wait();}catch(Exception e){}
}
System.out.print("firtd");
System.out.print(" ");
flag=1;
System.out.println(s2 +" Notifying: "+s1);
notify();
try{wait();s1=s2;Thread.currentThread().sleep(800);} catch(Exception e){}
}
if(s2.equals("two"))
{ if(flag==2)
{ flag=2;
System.out.println(s2 +" Waiting ");
s1=s2;
try{wait();}catch(Exception e){}
}
System.out.print("sectd");
System.out.print(" ");
flag=2;
System.out.println(s2 +" Notifying: "+s1);
notify();
try{wait();s1=s2;Thread.currentThread().sleep(800);} catch(Exception e){}
}
if(s2.equals("three"))
{ if (flag==3)
{ flag=3;
System.out.println(s1 +" Waiting ");
s1=s2;
try{wait();}catch(Exception e){}
}
System.out.print("thrtd");
System.out.print(" ");
flag=3;
System.out.println(s2 +" Notifying: "+ s1);
notify();
try{wait();s1=s2;Thread.currentThread().sleep(800);} catch(Exception e){}
}
}
}
}
public static void main(String ars[])
{
Thread.currentThread().setPriority(10);
Thread t1=new Thread(new Stwait(),"one");
t1.start();
t1.setPriority(4);
System.out.print(" out of main");
}
}
*****************************************************
end of code:
enjoy middling with java
Netharam
[This message has been edited by netharam ram (edited November 21, 2001).]