public class MyStack {
    int size;
    Object[] elem;
    
    public MyStack() {
	size = 0;
	elem = new Object[1];
    }

    public boolean isEmpty() {
	return size == 0;
    }

    private void grow() {
	Object[] newelem = new Object[2*size+1];
	System.arraycopy(elem, 0, newelem, 0, size);
	elem = newelem;
    }
    
    public void moveTopToStack(MyStack other) {
	if (other.size == other.elem.length)
	    other.grow();
	other.elem[other.size++] = this.elem[--this.size];
    }

    public void push(Object o) {
	if (size == elem.length)
	    grow();
	elem[size++] = o;
    }

    public String toString() {
	StringBuilder sb = new StringBuilder("[");
	for (int i = 0; i < size; i++) {
	    sb.append(elem[i]);
	    if (i < size-1)
		sb.append(",");
	}
	sb.append("]");
	return sb.toString();
    }

    public static void main(String[] param) throws InterruptedException {
	final MyStack a = new MyStack();
	final MyStack b = new MyStack();
	a.push("foo");
	b.push("baz");
	Thread t1 = new Thread("t1") {
		public void run() {
		    for (int i = 0; i < 3; i++) {
			while (a.isEmpty())
			    yield();
			a.moveTopToStack(b);
		    }
		}
	    };
	Thread t2 = new Thread("t2") {
		public void run() {
		    for (int i = 0; i < 3; i++) {
			while (b.isEmpty())
			    yield();
			b.moveTopToStack(a);
		    }
		}
	    };
	t1.start();
	t2.start();
	t1.join();
	t2.join();
	System.out.println(a);
	System.out.println(b);
    }
  }