Method join

java/Chapter 3/Question3_3/Stack.java:17–20

(Node above, Node below)

	}
	
	public void join(Node above, Node below) {
		if (below != null) below.above = above;
		if (above != null) above.below = below;
	}
	
	public boolean push(int v) {
		if (size >= capacity) return false;