public class Counter {
	int c;
	static Object lock = new Object();
	
	synchronized void increment() {
		this.c++;
	}
	
	public static void main (String arg[]) {
		Counter mycounter = new Counter();
		
		/* thread 1 */
		Thread t1 = new Thread(new Runnable() {
			@Override
			public void run() {
				for (int i = 0; i < 500; i++) {
					
					mycounter.increment();	
					System.out.println("t1:" + mycounter.c);
					
					if (mycounter.c == 250) {
						synchronized (lock) {
							try {
								lock.wait();
							} catch (InterruptedException e) {
								e.printStackTrace();
							}
						}
					}
				}		
			}			
		});
		t1.start();

		/* thread 2 */
		Thread t2 = new Thread(new Runnable() {
			@Override
			public void run() {
				for (int i = 0; i < 500; i++) {
					mycounter.increment();	
					System.out.println("t2:" + mycounter.c);
					if (mycounter.c == 450) {
						synchronized (lock) {
							lock.notifyAll();
						}
					}
				}			
			}			
		});
		t2.start();
		
		System.out.println("main:" + mycounter.c);
		
	}
}