Visitor

BobAndAlice.java

class WidthVisitor implements BoxVisitor {
	int visitBob(BobBox box) {
		return box.getWidth();
	}
  
  	int visitAlice(AliceBox box) {
		return Math.abs(box.getX2() - box.getX1());
	}
}

class HeightVisitor implements BoxVisitor {
	int visitBob(BobBox box) {
		return box.getHeight();
	}
  
  	int visitAlice(AliceBox box) {
		return Math.abs(box.getY2() - box.getY1());
	}
}