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 want to have a function passed in with a String param 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 method that takes the pointer would just accept StringFunction instance like so:

public void takingMethod(StringFunction sf) {    int i = sf.func('my string');    // do whatever ... } 

And would be called like so:

ref.takingMethod(new StringFunction() {     public int func(String param) {         // body     } }); 

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

ref.takingMethod(param -> bodyExpression);