// ---- Class for shared integer with lock ---------------------------

public class SharedInt {

    // Instance variables.
    public int value;
    private boolean locked;

    // Constructor.
    public SharedInt(int initVal) {
	value = initVal;
	locked = false;
    }

    // Method to acquire lock.
    // Waits until lock is available.
    // Allows exceptions thrown by wait() to bubble up.
    public synchronized void lock() throws InterruptedException {
	while (locked)
	    wait();
	locked = true;
    }

    // Method to release lock.
    // Wakes up any waiting threads.
    public synchronized void unlock() { 
	locked = false;
	notifyAll();
    }
}