How to create lambda expression for functional interface having generic method

Question

I have a functional interface

@FunctionalInterface
interface MyInterface {
    <T> T modify(Object);
}

I can create anonymous class for this interface

MyInterface obj = new MyInterface(){
    @Override
    <T> T modify(Object obj){
        return (T) obj
    }
}

How to create lambda expression for this.

MyInterface obj -> {return (T) obj;};  // ! ERROR as T is undefined

Check this question: http://stackoverflow.com/q/22588518/1679863 — Rohit Jain, Dec 19 '15 at 07:41
Factor your lambda into a method, and use a method reference. — Brian Goetz, Dec 19 '15 at 16:00

score 5 · Accepted Answer · answered Dec 19 '15 at 07:41

Generics at method scope cannot be used in lambda expressions. It will throw

Illegal lambda expression: Method modify of type MyInterface is generic

You need to set the generic at class scope.

@FunctionalInterface interface MyInterface<T> { T modify(Object obj); }

Then use it as follows:

MyInterface obj2 = o -> {return o;};

1 Answers1