Help with understanding a function object or functor in Java

Question

Can someone explain what a functor is and provide a simple example?

Answer 1

A functor is an object that's a function.

Java doesn't have them, because functions aren't first-class objects in Java.

But you can approximate them with interfaces, something like a Command object:

public interface Command {
    void execute(Object [] parameters); 
}

Updated on 18-Mar-2017:

Since I first wrote this JDK 8 has added lambdas. The java.util.function package has several useful interfaces.