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Groups > comp.lang.java.programmer > #3185

Partially overriding a method?

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I was wondering if it is possible to override a method but only for
certain sub-classes of the method that the super-class supports.

For example:

class MainClass {

    public static void main(String[] args) {

        System.out.println("Started");

        MainClass mc = new SubClass();

        mc.check("Testing");
        mc.check(7);

    }

    void check(Object x) {
        System.out.println(x.toString());
    }

}


class SubClass extends MainClass {

    void check(String x) {
        System.out.println("Sub class: " + x);
    }

}

The call to mc.check() calls the main class's version of the method.

However, if I change the sub-class to:

class SubClass extends MainClass {

    void check(Object x) {
        System.out.println("Sub class: " + x);
    }

}

then it uses the sub-class always.

One option would be something like:

class SubClass extends MainClass {

    void check(Object x) {
        if(x instanceof String) {
            check((String)x);
        } else {
            super.check(x);
        }
    }

    void check(String x) {
        System.out.println("Sub class: " + x);
    }

}

This would override and only use the sub-class for processing Strings.

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Thread

Partially overriding a method? "raphfrk@gmail.com" <raphfrk@gmail.com> - 2011-04-21 08:31 -0700
  Re: Partially overriding a method? Lew <noone@lewscanon.com> - 2011-04-21 12:42 -0400
  Re: Partially overriding a method? markspace <-@.> - 2011-04-21 11:37 -0700
    Re: Partially overriding a method? Lew <noone@lewscanon.com> - 2011-04-21 15:58 -0400
  Re: Partially overriding a method? Michal <kleku75@gmail.com> - 2011-04-21 21:00 +0200
  Re: Partially overriding a method? Roedy Green <see_website@mindprod.com.invalid> - 2011-04-21 12:59 -0700
  Re: Partially overriding a method? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-04-21 21:10 -0400
    Re: Partially overriding a method? "raphfrk@gmail.com" <raphfrk@gmail.com> - 2011-04-24 09:39 -0700

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