Object Oriented Programming

Lecture 7:Algorithm animation using strategy and factory patterns, The Adapter design pattern

www.hh.se/staff/jebe/oop2006/main.html

Last lecture Unit testing

Structured testing on units (classes)

Reduce complexity by incremental testing on small components

No clutter in the source code Demonstration of the JUnit

tool Module in Netbeans Exercise 10: using JUnit

Testing inSoftware development

Requirements analysis

Design

Implementationand unit testing

Integration andsystem testing

Maintenance

In this OOP Course

In the Software engineering course

Template Pattern Purpose: A generic Class for objects

which: Shares functionality (i.e. same concrete methods

in Java) But also has some method implementations that

need to be different (abstract) The common methods are encapsulated in

the template class We used Template pattern in

the Doublebuffered Animation Applet the Function Plotter

Structure of the Template patternAbstract Class

Concrete implementations (invariant parts)

Abstract methods

Subclass extending the template (Concrete class)

Implements the hookMethods

Generic Class

templateMethod()

hookMethod1()

hookMethod2()

Concrete Class

hookMethod1()

hookMethod2()

Strategy pattern Purpose: An abstraction to decouple

algorithms from its host Force provision of a set of required services

(methods) but with different implementations With strategy pattern we can implement

contractually compatible classes with different algorithms

A useful methodolgy to dynamically swap algorithms in a program

Design Pattern: Strategy

The plotter The abstract strategy

Concrete implementations

Context

ContextMethod()

Strategy

algorithm()

ConcreteStrategyA()

algorithm() algorithm()

ConcreteStrategyB()

Animation of Sorting Algorithms Applet to visualize

execution of sorting algorithms

It should be easy to adapt for different sort

algorithms different displays

Demonstrates usage of Factory, Strategy and Observer - Observable patterns

Sorting Algorithms Input to the Algorithm Sorter: an array of

Integers Choosing different sorting algorithms

executing with different complexities Bubble Sort O(n2) Quick Sort O(n*log n) Insertion Sort O(n2) ...

The framework should adapt to different algorithms and different display strategies

Generic Algorithm Animation – Design Issues

Algorithm Abstraction? Problem: How can we easily change between

different algorithms? Integration with Animation during sorting?

Problem: The screen should be redrawn after each iterative step, running the algorithm

Display Abstractions? Problem: We will also need a modular way to

hook different graphical displays

Starting the design of the Algorithm Animator

Two design pattern candidates: Template – Not flexible

since we want to assign any sorting algorithm after compile time (recall the function multiplotter from last lecture)

Strategy – More flexible since we can decouple the sort algorithms from the animator

We will use strategy pattern to separate the algorithm from animator

Design Pattern: Strategy

The Strategy interface

Concrete Sort algorithms

So we can render between each sort iteration!

Algorithm Animator

Sortalgorithm()

Strategy

sort()

BubbleSort

sort() sort()

QuickSort

The Sorting Abstraction Has an abstract sort method

Called by the Animator to start sorting Issue: How do we render the animation between each

swap during the sort? Solution: We implement a pause() function!

Will pause the sorting and render after each swap during the sorting process

Since all sorting algorithms involve swapping of two values Makes sense to factor swap into the sorting

abstraction Issue: How do we render the image after each swap?

Use a Animator reference to call: animator.pause(); We will use the Observer-Observable pattern!

The sorting abstraction

public abstract class SortAlgorithm extends java.util.Observable {

abstract void sort(int a[]); protected void pause(){

setChanged();notifyObservers();

} protected static void swap(int a[], int i, int j) {

int T;T = a[i]; a[i] = a[j]; a[j] = T;

}}

A concrete sorting algorithm

class BubbleSortAlgorithm extends SortAlgorithm { void sort(int a[]) { for (int i = a.length; --i>=0; ) for (int j = 0; j<i; j++) { if (a[j] > a[j+1]) swap(a, j, j+1); pause(); } }}

The algorithm animator The AlgorithmAnimator template

abstract method for initAnimator(); A an applet

Implements Runnable and Observer A thread controls frame delay

Performs animation of an abstract SortAlgorithm

The animation is controlled by Thread to handle frame delay The Observer Observable pattern for drawing

synchronisation

A Bubble sorter using the AlgorithmAnimator template

public class BubbleSorter

extends AlgorithmAnimator

{

protected void initAnimator(){

theAlgorithm = new BubbleSortAlgorithm();

}

}

How can we improve the design?

The different sort algorithms are strongly coupled to the specific Animator

We want the sorting algorithms be easily interchangable Loading algorithms at startup

We want the client (Algorithm Animator) be unaware of the concrete algorithms

Improving our design using the Factory Design Pattern

We can separate the creation of algorithms in a separate class

We call this class a Factory and it produces products (Sort Algorithms) of a certain type (Sorting Abstraction) Can be abstractly ”hooked” to the

animator The concrete algorithms will be

coupled to the Algorithm Factory instead of the Algorithm Animator

The Factory Design Pattern

Using Strategy to decouple the algorithms

The concrete Factory

Algorithm Animator

Sortalgorithm()

SortingAlgorithm

sort()

BubbleSort

sort() sort()

QuickSort

Algorithm Factory

makeSortAlgorithm()

StaticAlgoFactory

makeSortAlgorithm()

StaticAlgoFactory Input: the name of a sorting algorithm

(String) Output: A concrete instance of the

abstract SortAlgorithm (a product) The Contractual Interface:

abstract makeSortAlgorithm(String algName){...}

Must be defined by every concrete AlgoFactory Binds the actual algorithm to the animator

The Strategy abstraction of Factory and a concrete implementation

public interface SortAlgorithmFactory{

SortAlgorithm makeSortAlgorithm(String name);

}

Algorithm Animator

Sortalgorithm()

SortingAlgorithm

sort()

BubbleSort

sort() sort()

QuickSort

Algorithm Factory

makeSortAlgorithm()

StaticAlgoFactory

makeSortAlgorithm()

A concrete Algorithm Factory

public class StaticAlgoFactoryimplements SortAlgorithmFactory {

public SortAlgorithmmakeSortAlgorithm(String name) {

if ("BubbleSort".equals(name)) return new BubbleSortAlgorithm(); else if ("QuickSort".equals(name)) return new QuickSortAlgorithm(); else return new BubbleSortAlgorithm(); }}

Using the improved AlgorithmAnimator

import java.awt.*;

public class Sort extends AlgorithmAnimator{ protected void initAnimator()

{String algoName = getParameter("alg");SortAlgorithmFactory factory = new

StaticAlgoFactory();theAlgorithm =

factory.makeSortAlgorithm(algoName); }}

Invoking the AlgorithmAnimation applet

<applet code=Sort.class width=100 height=100>

<param name = alg value = QuickSort>

</applet>

Further improvement: Decoupling the SortDisplay

public int getArraySize() method to provide the arraysize so we

know the maximum bars we can draw and animate using this display

public void Display(int[] a, Graphics g, Dimension d) The abstract drawing method, to be

called by paint To be implemented as exercise!

New Design Pattern: Adapter

A design pattern that can be used to: reuse classes without modifying the

code, instead we convert the interface! narrow interfaces when just needing a

small subset of the methods

Simple example: Narrowing of thye MouseListener with MouseAdapter

Some classes have an implementation which does not ”fit” the requirements

Or we might only need few of the availabe methods Ex. listening for mouse actions

MouseAdapter is a class implementing the MouseListener interface The adapter defines all MouseListener methods

empty (No action as default) By extending the MouseAdapter we only have to

override the methods we need in the mouse listener interface

The MouseListener interfacevoid mouseClicked(MouseEvent e);

Invoked when the mouse button has been clicked (pressed and released) on a component.

void mouseEntered(MouseEvent e); Invoked when the mouse enters a component.

void mouseExited(MouseEvent e); Invoked when the mouse exits a component.

void mousePressed(MouseEvent e); Invoked when a mouse button has been pressed on a component. void mouseReleased(MouseEvent e);

Invoked when a mouse button has been released on a component.

The MouseAdaptervoid mouseClicked(MouseEvent e){/* no action */}

Invoked when the mouse has been clicked on a component.

void mouseEntered(MouseEvent e) {/* no action */}Invoked when the mouse enters a component.

void mouseExited(MouseEvent e) {/* no action */}Invoked when the mouse exits a component.

void mousePressed(MouseEvent e) {/* no action */}Invoked when a mouse button has been pressed on a component.

void mouseReleased(MouseEvent e) {/* no action */}

Invoked when a mouse button has been released on a component.

A Simple MouseClick listenerPublic MouseClick extends MouseAdapter{

void mouseClicked(MouseEvent e){

System.out.println(”Disco!”);

}

/**

* Other MouseListener methods can be omitted

**/

}

Structure of the Adapter pattern – Class Adapter

Client Target

doStuff()

Adapter

doStuff()

Adaptee

doSomeTask()

doStuff(){….doSomeTask();…return result;

}

Structure of the Adapter pattern – Object Adapter

Client Target

doStuff()

Adapter

doStuff()

Adaptee

doSomeTask()

adaptee.doSomeTask();