In this case study, we design and implement an immutable abstract data type of finite functions that builds on our AListWithKeyIterator<K,V> example to define a class that will implement the entire java.util.Map<K,V> interface.

The IMap<K,V> interface we define in this lesson extends java.util.Map<K,V>.

Our first implementation of the IMap<K,V> reuses our implementation of AListWithKeyIterator<K,V> from the previous lesson by composing its association lists with classes that add many new methods, most of them inherited from an abstract base class defined in Java's java.util package: AbstractMap<K,V>.

The Map<K,V> interface includes some operations that have side effects. Luckily for us, all of those side-effecting operations are optional. That means we can implement an ADT of immutable finite maps by arranging for all of the side-effecting methods of the Map<K,V> interface to throw an UnsupportedOperationException if those methods are ever called.

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© Mitchell Wand, 2012-2015
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
The work has been modified by William D Clinger in these ways and more: conversion from PowerPoint to HTML, and from Racket to Java.