Event Bus in 58 lines of Java

EventBus.java

package site.hackery.photon;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.BooleanSupplier;
import java.util.function.Consumer;

import static java.util.Arrays.asList;

public class EventBus {
    public interface Handler<T> {
        void handle(T event);
    }

    public interface Registrator<T> {
        void to(Handler<T> handler);

        default void when(BooleanSupplier condition, Handler<T> handler) {
            to(event -> {
                if (condition.getAsBoolean()) {
                    handler.handle(event);
                }
            });
        }
    }

    private static Map<Class<?>, List<Handler>> map = new HashMap<>();

    public static <T> Registrator<T> register(Class<T> cls) {
        return handler -> {
            map.putIfAbsent(cls, new ArrayList<>());
            map.get(cls).add(handler);
        };
    }

    public static <T> void post(T event) {
        forAllSuperclasses(event.getClass()).invoke(cls -> map.getOrDefault(cls, new ArrayList<>()).forEach(handler -> handler.handle(event)));
    }

    private interface OnEachClass {
        void invoke(Consumer<Class<?>> cls);
    }

    private static OnEachClass forAllSuperclasses(Class<?> clazz) {
        return action -> {
            Class<?> superCls = clazz;
            while (superCls != Object.class) {
                action.accept(superCls);
                asList(superCls.getInterfaces()).forEach(interfaceCls -> {
                    action.accept(interfaceCls);
                });
                superCls = superCls.getSuperclass();
            }
        };
    }
}