Exam LAb Threads Problem

[Mohit G Gupta]

 public class A extends Thread{

     public static void doDelay(long t){

          try{
               Thread.sleep(t);
          }catch(InterruptedException e){
               System.out.print("Ex-A ");
          }

     }

     public void run(){
          doDelay(1000);
          halt();
     }

     public void halt(){

          try{
               this.wait();
          }catch(Exception e){
               System.out.print("Ex-B ");
          }

     }

     public static void main(String args[])throws Exception{
          A a=new A();
          Thread t=new Thread(a);
          t.start();
          doDelay(100);
          a.interrupt();
          doDelay(2000);
          t.notifyAll();
     }

}   

is it necessary to have wait,notify in synchronized block or method

[Harikrishna Gorrepati]

Yes. wait(), notify() and notifyAll() methods must be called withing synchronized context( synchronized block, synchronized method)..These methods are not in SCJP exam as per other ranchers comments. Serialization is also not in the exam it seems.

[Rohit Ramachandran]

wait is thrown and caught. But t.notifyAll() throws an IllegalMonitorStateException.

[Trivikram Kamat]

Rohit Ramachandran wrote:wait is thrown and caught

Actually, wait() is not an exception which can be thrown.
IllegalMonitorStateException is (also) thrown when wait() is called, as method is not synchronized.
But in that case, Ex-B is printed.

[Trivikram Kamat]

mohitkumar gupta wrote:
is it necessary to have wait,notify in synchronized block or method

Yes, it's necessary.

Wait and Notify provides a means of communication between threads which are synchronized on the same object.
When a Thread calls wait() method in synchronized context, it releases the object lock and waits.
Invoking notify() method from other thread occupying that object lock wakes up the waiting thread.