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Unit 16Iterator

Summary prepared by Kirk Scott

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Design Patterns in JavaChapter 28

Iterator

Summary prepared by Kirk Scott

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The Introduction Before the Introduction

• This chapter is divided into 3 parts:• 1. Ordinary Iteration• 2. Thread-Safe Iteration• 3. Iterating over a Composite• I am going to dispense with each part in about

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Ordinary Iteration

• This refers to the Iterator class with three methods: hasNext(), next(), and remove()

• The Iterable interface, which means a domain class has an iterator() method that returns an iterator on an instance of that class

• For each loops, which allow you to traverse the contents of a collection with an iterator

• This is all standard stuff, and it’s assumed that you are at least generally familiar with it

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Thread-Safe Iteration

• This is beyond the scope of this course• No doubt it is a fascinating topic, full of tricks

and traps, but if you don’t know what threads are, it’s pointless to talk about iteration in that context

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Iterating over a Composite

• This is the part of the chapter where the book develops some code, making the classes of the Composite design pattern implement the Iterable interface

• This means also developing a hierarchy of Iterator classes for components, leaves, and composites

• This is relatively complex

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• As an introduction to iteration as a design pattern it would be better to implement iterability over a simpler programmer developed collection class

• For example, the general idea of a stack came up in the discussion of the Memento design pattern, so that data structure should be familiar

• Keep this in mind as an assignment or test question problem

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The End

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• All of the book diagrams for the chapter are tipped in on the following overheads for future reference

• They are not needed in this iteration of the overheads and you’re not responsible for what they contain

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