thread question

[Harvinder Singh]

//compiles but gives a runtime exception that thread is not the owner
Question 22)
Which statement is true of the following code?
public class Agg{
public static void main(String argv[]){
Agg a = new Agg();
a.go();
}
public void go(){
DSRoss ds1 = new DSRoss("one");
ds1.start();
}
}
class DSRoss extends Thread{
private String sTname="";
DSRoss(String s){
sTname = s;
}
public void run(){
notwait();
System.out.println("finished");
}
public void notwait(){
while(true){
try{
System.out.println("waiting");
wait();
}catch(InterruptedException ie){}
System.out.println(sTname);
notifyAll();
}
}

}
1) It will cause a compile time error
2) Compilation and output of "waiting"
3) Compilation and output of "waiting" followed by "finished"
4) Runtime error, an exception will be thrown

[Jose Botella]

Hi,
never call notify or wait out of a synchronized block/method. There will be a RuntimeException, thus answer is 4)
To avoid the IllegalMonitorStateException the thread that calls object.notify() must also have entered a synchronized block like:
synchronized(object) {
..
object.notify();
}
or be executing a synchronized method of object. By either of these techniques the thread executing object.notify() is owner (has adquired) the monitor of object.
Please see The Java Tutorial for more.