November 2004 91.3913 Ron McFadyen 1

Composite Pattern

A composite is a group of objects in which some objects contain others; one object may represent groups, and another may represent an individual item, a leaf.

November 2004 91.3913 Ron McFadyen 2

Composite Pattern

Generic UML class diagram

Component

Operation()

Leaf

Operation()

Composite

Operation()Other()

*Client

November 2004 91.3913 Ron McFadyen 3

Composite Pattern

Consider the handout from Refactoring by Martin Fowler

•“Refactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code yet improves its internal structure.”•P 76 Long Method:

•“object programs … short methods”•“the longer a procedure is, the more difficult it is to understand”•“A heuristic we follow is that whenever we feel the need to comment something, we write a method instead”•“How do you identify the clumps of code to extract? A good technique is to look for comments. They often signal a kind of semantic distance.”

November 2004 91.3913 Ron McFadyen 4

Composite Pattern

Refactoring by Martin Fowler

•Figure 4.1. The composite structure of tests

Test

TestSuite TestCase

FileReaderTester

junit.framework

*

November 2004 91.3913 Ron McFadyen 5

Composite Pattern

Junit is a testing framework for Java (If interested, see www.junit.org)

Any class that contains a test, must be subclassed from TestCase

Tests can be grouped into test suites

Pages 92-93 illustrate how to use junit to manage a suite of tests

We’ll look at an example for NextGenPOS