I use this handler class when I want to have dynamically typed, variable length parameters.

Example.java

registerStudent(student, new HandlerChain<RegistrationStep>()
	.on(RegistrationStep.NEW_STUDENT, new FlexibleHandler() {
		void handle(NewRegistrant registrant) {
			System.out.println(registrant.info());
		}
	})
	.on(RegistrationStep.USER_EXISTS, new FlexibleHandler() {
		void handle(NewRegistrant registrant, UserContainer existingUser) {
			System.out.println(registrant.info());
			System.out.println(existingUser.info());
		}
	})
);

FlexibleHandler.java

public class FlexibleHandler {

	// add whatever methods you want!

	public final void invoke(Object...args) {
		for (Method method : this.getClass().getDeclaredMethods()) {
			Object[] newArgs = new Object[method.getParameterTypes().length];
			System.arraycopy(args, 0, newArgs, 0, newArgs.length);

			try {
				method.setAccessible(true);
				method.invoke(this, newArgs);
			} catch (IllegalAccessException e) {
				throw new RuntimeException(e);
			} catch (InvocationTargetException e) {
				throw new RuntimeException(e.getCause());
			}
		}
	}
}