Java 8 lambda Void argument

Question

Let\'s say I have the following functional interface in Java 8:

interface Action {
   U execute(T t);
}

And for some cases I ne

Answer 1

You can create a sub-interface for that special case:

interface Command extends Action {
  default Void execute(Void v) {
    execute();
    return null;
  }
  void execute();
}

It uses a default method to override the inherited parameterized method Void execute(Void), delegating the call to the simpler method void execute().

The result is that it's much simpler to use:

Command c = () -> System.out.println("Do nothing!");