multiple inheritance in java : implementing interfaces

Question

I have a class that implements Comparator but not that I need my class to be Serializable How can I implement both of them ?

public class A implements Comparator<A>
{
}

To expand on all of the answers, in Java you can only extend a single class, but you can implement unlimited interfaces. — aruisdante
– aruisdante, Commented Mar 16, 2014 at 19:51

arshajii · Accepted Answer · 2014-03-16 19:56:05Z

2

It's a common misconception that Java does not have multiple inheritance. It doesn't have multiple inheritance of state, but it does have multiple inheritance of (declarations of) behavior, which is shown through interfaces. So you can have a single class implement multiple interfaces:

public class A implements Comparator<A>, Serializable {
}

edited Mar 16, 2014 at 19:56

answered Mar 16, 2014 at 19:50

arshajii

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5 Comments

aruisdante Over a year ago

Not quite right. It has multiple inheritance of declarations of behavior. Interfaces lack implementation, so it's not truly multiple inheritance of behavior. Essentially, it's a bridge between true multiple-inheritance and duck-typing.

chrylis -cautiouslyoptimistic- Over a year ago

Technically, it still (as of 7) doesn't have inheritance of behavior, but at least that's kinda changing.

arshajii Over a year ago

I guess you two are technically correct, at least for a few more days until Java 8 comes out. I'll try to reword the answer.

arshajii Over a year ago

@aruisdante I updated the answer in accordance with your comment. Downvoter: please see the revised answer.

Night Mare Over a year ago

@arshajii could you add more explanition about state and behavior, I don't understand how two are different ?

ruhungry · Accepted Answer · 2014-03-16 19:50:20Z

1

import java.io.Serializable;
import java.util.Comparator;

public class A implements Comparator<A>, Serializable {

    @Override
    public int compare(A arg0, A arg1) {
        return 0;
    }
}

answered Mar 16, 2014 at 19:50

ruhungry

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Comments

Raul Guiu · Accepted Answer · 2014-03-16 19:50:35Z

0

You can implement more than one interface, simply separate them with commas:

class A implements Comparator<A>, Serializable {
}

answered Mar 16, 2014 at 19:50

Raul Guiu

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Comments

oschlueter · Accepted Answer · 2014-03-16 19:50:43Z

0

You can extend only one superclass but you can implement as many interfaces as you like, e.g.

public class A extends B implements Comparator<A>, Serializable {
}

answered Mar 16, 2014 at 19:50

oschlueter

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