class Operation{
private int i = 0;
public synchronzied void increment(){
k++;
while(k==1) this.notify();
}
public synchronzied void decrement(){
while(k < 1) this.wait();
k--;
}
}
//main()
Operation op = new Operation();
new Thread(new Runnable(){op.increment()}).start();
new Thread(new Runnable(){op.increment()}).start();
new Thread(new Runnable(){op.decrement()}).start();
new Thread(new Runnable(){op.decrement()}).start();