LambdaBehavior.java

public class LambdaBehavior {
    interface Mixin {
        Map<Mixin, String> backingMap = Collections.synchronizedMap(new WeakHashMap<>());
        default String getName() { return backingMap.get(this); }
        default void setName(String name) { backingMap.put(this, name); }
    }

    interface X extends Runnable, Mixin {}

    static X makeI() { return () -> System.out.println("x"); }

    static X makeII() { return new X() {
        @Override
        public void run() {
            System.out.println("X");
        }
    }; }

    static X makeIII(String s) { return () -> System.out.println(s); }

    @Test
    public void thing() {
        X xi1 = makeI();
        X xi2 = makeI();
        xi1.setName("x1");
        xi2.setName("x2");

        X xii1 = makeII();
        X xii2 = makeII();
        xii1.setName("x1");
        xii2.setName("x2");

        X xiii1 = makeIII("");
        X xiii2 = makeIII("");
        xiii1.setName("x1");
        xiii2.setName("x2");


        System.out.println("Lambda with no implicit closure variable:");
        System.out.println(xi1.getName());
        System.out.println(xi2.getName());

        System.out.println("Anonymous class:");
        System.out.println(xii1.getName());
        System.out.println(xii2.getName());

        System.out.println("Lambda with implicit closure variable:");
        System.out.println(xiii1.getName());
        System.out.println(xiii2.getName());
    }
}

//Outputs:
// Lambda with no implicit closure variable:
// x2
// x2
// Anonymous class:
// x1
// x2
// Lambda with implicit closure variable:
// x1
// x2

Expanded on concept found in https://kerflyn.wordpress.com/2012/07/09/java-8-now-you-have-mixins/ to poke further at the behavior of lambdas and anonymous implementations.