This question was asked to me in an interview. Before I told him this,
Once a thread injects any synchronized method into an instance, no other thread can enter any other synchronized method in the same instance.
Consider a snippet:
Q1:
public class Q1 {
int n;
boolean valueSet = false;
synchronized int get() {
while (!valueSet)
try {
wait();
} catch (InterruptedException e) {
System.out.println("InterruptedException caught");
}
System.out.println("Got: " + n);
valueSet = false;
notify();
return n;
}
synchronized void put(int n) {
while (valueSet)
try {
wait();
} catch (InterruptedException e) {
System.out.println("InterruptedException caught");
}
this.n = n;
valueSet = true;
System.out.println("Put: " + n);
notify();
}
}
Producer1:
public class Producer1 implements Runnable {
Q1 q;
Producer1(Q1 q) {
this.q = q;
new Thread(this, "Producer").start();
}
@Override
public void run() {
int i = 0;
while (true) {
q.put(i++);
}
}
}
Consumer1
public class Consumer1 implements Runnable {
Q1 q;
Consumer1(Q1 q) {
this.q = q;
new Thread(this, "Consumer").start();
}
@Override
public void run() {
while (true) {
q.get();
}
}
}
PC1:
public class PC1 {
public static void main(String args[]) {
Q1 q = new Q1();
new Producer1(q);
new Consumer1(q);
System.out.println("Press Control-C to stop.");
}
}
So, he asked, as soon as you created this thread new Producer1(q), then, according to you, the method synchronized int get()should be blocked by the same thread, that is new Producer1(q), when it turned to synchronized int put(), I said yes.
But I checked in eclipse, get can be called new Consumer1(q). The program works great.
Where am I going wrong?
O / P:
