How to override two and more methods of interface using Lambda expression?

Question

1.InterfaceOne is one interface having two methods ,my question i how to override that 2 methods using Lambda expression?

interface InOne{

    void m1();
    void m2();
}
public class LambdaExpForTwomethodsInInterface {

    public static void main(String[] args) {

        //For One method overriding
        InOne one=()->{
            System.out.println("InOne m1");
        };
        one.m1();
    }
}

2.If there are 5 methods in interface,but i want to override only one method,is there any way to that using Lambda exp?

You implement methods from interface, don't override. Override is from class — Evgeni Enchev
– Evgeni Enchev, Commented Feb 8, 2019 at 12:01
Implimenting interface methods is called overriding right.That why mentioned the term @ Evgeni — mae
– mae, Commented Feb 8, 2019 at 12:09

Naman · Accepted Answer · 2019-02-08 16:21:29Z

4

is there any way to that using Lambda exp?

No, they are meant to be referencing only FunctionalInterfaces.

how to override that 2 methods using Lambda expression?

Though not possible using a lambda expression, you can still use an anonymous class to instantiate them:

InOne one = new InOne() {
    @Override
    public void m1() {

    }

    @Override
    public void m2() {

    }
};

edited Feb 8, 2019 at 16:21

answered Feb 8, 2019 at 11:59

Naman

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2 Comments

mae Over a year ago

You mean ,Lambda deal only with funtional interface?

Naman Over a year ago

@mae yup, precisely... Would refer you to read further details around stackoverflow.com/questions/23342499/…

Oleg Cherednik · Accepted Answer · 2019-02-08 12:11:48Z

0

interface InOne {
    default void m1() {}
    default void m2() {}
}

Implement

InOne one = new InOne() {
    @Override
    public void m1() {
        System.out.println("InOne m1");
    }
};

one.m1();  // InOue m1
one.m2();  // <nothing>

Implement using Lambda

@FunctionalInterface
interface InOneM1 {
    void m1();
}

@FunctionalInterface
interface InOneM2 {
    void m2();
}

InOneM1 oneM1 = () -> System.out.println("InOne m1");
InOneM2 oneM2 = () -> System.out.println("InOne m2");

oneM1.m1();
oneM2.m2();

edited Feb 8, 2019 at 12:11

answered Feb 8, 2019 at 12:00

Oleg Cherednik

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4 Comments

mae Over a year ago

If it is dealing only with Funtional interfaces ,then how it is dealing reducing code and giving much importance.I mean generally ,we have more then one methods in interfaces of our projects right..!

Oleg Cherednik Over a year ago

Right. Lambda works only with Functional Interface

Naman Over a year ago

@oleg.cherednik <empty string> rather shall mean void... by the way, there is another combination as well one of them being default and another being abstract to term the interface as FunctionalInterface... but that should be considered while approaching towards designing them.

Naman Over a year ago

@mae not every interface is supposed to be represented using lambdas.. you can still have interfaces which are not FunctionalInterface.. but in order to make use of them, one can design the interfaces and their hierarchy as such.

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