How can I store a method in a variable in Java 8?

Question

Is it possible to store a method into a variable? Something like

 public void store() {
     SomeClass foo = ;
     //...
     String          


        

Answer 1

Yes, you can have a variable reference to any method. For simple methods it's usually enough to use java.util.function.* classes. Here's a working example:

import java.util.function.Consumer;

public class Main {

    public static void main(String[] args) {
        final Consumer simpleReference = Main::someMethod;
        simpleReference.accept(1);

        final Consumer another = i -> System.out.println(i);
        another.accept(2);
    }

    private static void someMethod(int value) {
        System.out.println(value);
    }
}

If your method does not match any of those interfaces, you can define your own. The only requirement is that is must have a single abstract method.

public class Main {

    public static void main(String[] args) {
    
        final MyInterface foo = Main::test;
        final String result = foo.someMethod(1, 2, 3);
        System.out.println(result);
    }

    private static String test(int foo, int bar, int baz) {
        return "hello";
    }

    @FunctionalInterface // Not required, but expresses intent that this is designed 
                         // as a lambda target
    public interface MyInterface {
        String someMethod(int foo, int bar, int baz);
    }
}