FancyStuff.java

import java.util.Collection;
import java.util.HashSet;

class TestKlasse {
    public TestKlasse() {
    }
}

interface Buildable<T> {
    void build(int x, Collection<T> c);
}

interface Destroyable<T> {
    void destroy(T x);
}

public class FancyStuff {
    public static void main(String[] args) {

        Buildable b = (Buildable<TestKlasse>) (count, c) -> {
            for (int i = 0; i < count; i++) {
                c.add(new TestKlasse());
            }
        };

        Destroyable destroyer = (Destroyable<TestKlasse>) (testKlasse)
                -> System.out.println(testKlasse + "is kapuut jetzt");

        Collection set = new HashSet();
        b.build(20, set);


        set.forEach(destroyer::destroy);
    }
}