CODEWITHSUNDEEP
javalambdainterfacefunctional-programmingjava-8
Shubham Jain
Shubham Jain

Reputation: 1984

How do I implement two abstract methods in Java using lambdas?

I have a Functional Interface in the code below which has one abstract method and one object method override. So when I write Lambda expression for that , how can I implement my equals method.

import static java.lang.System.out;

public class Test {
    public static void main(String[] args) {
        AddToString test = a -> (a + " End");
        out.println(test.stringManipulation("some string"));
        out.println(test.increment(5));
        out.println(test.equals(null));
    }
}

@FunctionalInterface
interface AddToString {
    String stringManipulation(String a);
    default int increment(int a) { return a+1; }
    @Override
    public boolean equals(Object obj);
}

One way to do that is to create Anonymous class like given below, but is there a better method using lambda expressions - 

public class Test {
    public static void main(String[] args) {
        AddToString test = new AddToString() {
            public String stringManipulation(String a) {
                return a + " End";
            }
            @Override
            public boolean equals(Object Obj) {
                //Just testing whether it overrides
                return 5==5;
            }
        };
        out.println(test.stringManipulation("some string"));
        out.println(test.increment(5));
        out.println(test.equals(null));
    }
}

Upvotes: 2

Views: 984

Answers (1)

T.J. Crowder
T.J. Crowder

Reputation: 1074355

You can't. If you need to override equals, you'll need to create a class (anonymous or otherwise), you can't do it with a lambda.

Upvotes: 7

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