IllegalMonitorStateException while calling wait() in run()

Question

I have created an java thread and passed an stack reference to it\'s constructor, which initialize thread stack reference. In run method i have created an synchronized block

Answer 1

For wait() (or notify()) to work, you must call it on the same object. What you have now is the same as

 synchronized (stack) {
    if(stack.isEmpty()){
        try {
            this.wait();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
 }  

instead you should do

 synchronized (stack) {
    if(stack.isEmpty()){
        try {
            stack.wait(); // wait on the same object synchronized.
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
 }  

Note: as wait can wake spuriously you have do this in a loop or your method could return prematurely.

 synchronized (stack) {
    while (stack.isEmpty()){
        try {
            stack.wait(); 
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
 }