CSC/ECE 517 Fall 2011/ch2 2c ac

Mixin versus Interface

Introduction

[To be changed] Functionality such as Comparable is done in Java with interfaces and in Ruby with mixins. Is there an advantage in using one or another? Consider other behaviors achieved with mixins in Ruby: Singleton, Enumerable, and DataMapper, for example. Could you accomplish these with interfaces in Java? Does this mean that mixins are more powerful? Or can interfaces achieve some purposes that mixins can't?

Definition

Multiple Inheritance

Multiple inheritance is a feature of some object-oriented computer programming languages in which a class can inherit behaviors and features from more than one superclass. (From Wikipedia, http://en.wikipedia.org/wiki/Multiple_inheritance)

Interfaces in Java

http://download.oracle.com/javase/tutorial/java/concepts/interface.html

Modules in Ruby

Modules in Ruby are a way to group together methods, classes and constants. They are similar to namespaces in languages such as C++. (From lecture 6 note)

Mixin using Modules

The most interesting use of modules is to define mixins. When you include a module within a class, all its functionality becomes available to the class. Not only can modules contain class methods; they can also contain instance methods. (From lecture 6 note)

Examples

Singleton

Java Implementation

public class Singleton  {
    private static final Singleton instance = new Singleton();
 
/**
Private constructor prevents instantiation from other classes
**/
    private Singleton() {
    }
 
    public static Singleton getInstance() {
        return instance;
    }
}