子类中的访问方法

Question

I have used the code:

//change size of raven
birdsByKey.get(instructions[0]).SizeRaven(newSize);

in order to try change the size of the raven.

What should I do to use the following method (in class "Raven")?

Answer 1

birdsByKey.get() is going to return a Bird . A Bird won't have a changeRavenSize() method (since that is unique to a Raven).

You need something like:

Bird b = birdsByKey.get(instructions[0]);
if (b instanceof Raven) {
    Raven r = (Raven)b;
    r.changeSizeRaven(newSize);
}

As EJP mentions, you really want a changeSize() method for Bird which Raven will override. Then you code becomes

birdsByKey.get(instructions[0]).changeSize(newSize);

the first way you need to edit every time you add a new type of bird. The second way just add as many birds as you like and it'll just keep working...