What's the nearest substitute for a function pointer in Java?

Question

I have a method that's about ten lines of code. I want to create more methods that do exactly the same thing, except for a small calculation that's going to change one line of code. This is a perfect application for passing in a function pointer to replace that one line, but Java doesn't have function pointers. What's my best alternative?

Answer 1

Anonymous inner class

Say you require to have a function transferred in with a Stringparam that returns an int.

First, you have to define an interface with the function as its only member if you can't reuse an existing one.

interface StringFunction {

    int func(String param);

}

A way that takes the pointer would just allow StringFunction instance like so:

public void takingMethod(StringFunction sf) {

   int i = sf.func("my string");

   // do whatever ...

}

And would be named like so:

ref.takingMethod(new StringFunction() {

    public int func(String param) {

        // body

    }

});

 In Java 8, you could call it with a lambda expression:

ref.takingMethod(param -> bodyExpression);