Question

Given the following situation (UML below),

If Y has the method:

public void PrintWs();

and X has:

ArrayList <P> myPs = new ArrayList();

Y y = new Y();
Z z = new Z();
myPs.add(y);
myPs.add(z);

How do I loop through each myPs object and call all Ys PrintWs (without using instanceof)?

http://starbucks.mirror.waffleimages.com/files/68/68c26b815e913acd00307bf27bde534c0f1f8bfb.jpg

Sorry, to clarify:

• Z contains 1 Y object.
• Y and Z are both subclasses of P
• The image seems to work if you refresh – My reputation is too low to upload images, so I will edit when I acquire 15 points 🙂

Answer 1

You can’t – assuming you only want to try to call PrintWs on instances of Y, you need to determine which references are pointing at instances of Y… and that’s where you use instanceof. (You could use Y.class.isInstance(p) but that’s just the same thing in a slightly different form.)

Of course if you can make P contain a no-op PrintWs which is then overridden in Y, then you can call it on everything in the list…