子类java中的“覆盖”超类成员

Question

Kind of a noob question, this, but I cannot figure it out.

This is animal.java. I want it to be a superclass for all animal subclasses. It's in the same package as all the subclasses.

public class Animal {
    protected static String call = "Animals make noises, but do not have a default noise, so we're just printing this instead.";
        public static void sound()
        {
            System.out.println(call);
        }
}

This is cow.java

class Cow extends Animal {
    call = "moo";
}

Evidently, this does not run. But I want to be able to run Cow.sound() and have the output read "moo". I also want to be able to create more classes that override the 'call' with their own string. What should I be doing instead?

Answer 1

You can't override instance variables. You can only override methods. You can override the sound method (once you change it to an instance method, since static methods can't be overridden), or you can override a method that sound will call (for example getSound() ). Then each animal can returns its own sound :

public class Animal {
    static String call = "Animals make noises, but do not have a default noise, so we're just printing this instead.";
    public void sound()
    {
        System.out.println(getSound ());
    }

    public String getSound ()
    {
        return call;
    }
}

class Cow extends Animal {
    @Override
    public String getSound ()
    {
        return "moo";
    }
}

Answer 2

Variables are never overriden, so sub class variable replacing supercall variable will not be possible. Another option was to override the method but then its static, static also cannot be overridden.

So with current setup its not possible unless you look to override non static methods.