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Design Pattern
hqzhang edited this page Oct 24, 2017
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- Singleton(just one instance) ===Obj.getInstance()
class SingletonObj {
//create an object of SingleObject
private static SingletonObj instance = new SingletonObj();
//make the constructor private so that this class cannot be
//instantiated
private SingletonObj(){}
//Get the only object available
public static SingletonObj getInstance(){
return instance;
}
public void showMessage(){
System.out.println("Hello World!");
}
}
public class Singleton {
public static void main(String[] args) {
//illegal construct
//Compile Time Error: The constructor SingleObject() is not visible
//SingleObject object = new SingleObject();
//Get the only object available
SingletonObj object = SingletonObj.getInstance();
//show the message
object.showMessage();
}
}
- factory(wrap several class) ===obj.getSpecificClass(“xxxClass”);
interface Shape { void draw(); }
class Square implements Shape {
public void draw() {
System.out.println("Inside Square::draw() method.");
}
}
class Circle implements Shape {
public void draw() {
System.out.println("Inside Circle::draw() method.");
}
}
class ShapeFactory {
//use getShape method to get object of type shape
public Shape getShape(String shapeType){
if(shapeType == null){
return null;
}
if(shapeType.equalsIgnoreCase("CIRCLE")){
return new Circle();
} else if(shapeType.equalsIgnoreCase("SQUARE")){
return new Square();
}
return null;
}
}
public class FactoryDemo {
public static void main(String[] args) {
ShapeFactory shapeFactory = new ShapeFactory();
//get an object of Circle and call its draw method.
Shape shape1 = shapeFactory.getShape("CIRCLE");
shape1.draw();
//get an object of Square and call its draw method.
Shape shape3 = shapeFactory.getShape("SQUARE");
shape3.draw();
}
}
- Iterator new NameRepository().getIterator();
interface Iterator {
public boolean hasNext();
public Object next();
}
interface Container {
public Iterator getIterator();
}
class NameRepository implements Container {
public String names[] = {"Robert" , "John" ,"Julie" , "Lora"};
@Override
public Iterator getIterator() {
return new NameIterator();
}
private class NameIterator implements Iterator {
int index;
@Override
public boolean hasNext() {
if(index < names.length){
return true;
}
return false;
}
@Override
public Object next() {
if(this.hasNext()){
return names[index++];
}
return null;
}
}
}
public class IteratorDemo {
public static void main(String[] args) {
for(Iterator iter = new NameRepository().getIterator(); iter.hasNext();){
String name = (String)iter.next();
System.out.println("Name : " + name);
}
}
}
- Adapter new Audioplay().play(“mediatype”,”filename”);
interface MediaPlayer {
public void play(String audioType, String fileName);
}
interface AdvancedMediaPlayer {
public void playVlc(String fileName);
public void playMp4(String fileName);
}
class VlcPlayer implements AdvancedMediaPlayer{ //2
@Override
public void playVlc(String fileName) {
System.out.println("Playing vlc file. Name: "+ fileName);
}
@Override
public void playMp4(String fileName) {
//do nothing
}
}
class Mp4Player implements AdvancedMediaPlayer{ //2
@Override
public void playVlc(String fileName) {
//do nothing
}
@Override
public void playMp4(String fileName) {
System.out.println("Playing mp4 file. Name: "+ fileName);
}
}
class MediaAdapter implements MediaPlayer { //1
AdvancedMediaPlayer advancedMusicPlayer;
public MediaAdapter(String audioType){
if(audioType.equalsIgnoreCase("vlc") ){
advancedMusicPlayer = new VlcPlayer();
} else if (audioType.equalsIgnoreCase("mp4")){
advancedMusicPlayer = new Mp4Player();
}
}
@Override
public void play(String audioType, String fileName) {
if(audioType.equalsIgnoreCase("vlc")){
advancedMusicPlayer.playVlc(fileName);
}else if(audioType.equalsIgnoreCase("mp4")){
advancedMusicPlayer.playMp4(fileName);
}
}
}
class AudioPlayer implements MediaPlayer { //1
MediaAdapter mediaAdapter;
@Override
public void play(String audioType, String fileName) {
//inbuilt support to play mp3 music files
if(audioType.equalsIgnoreCase("mp3")){
System.out.println("Playing mp3 file. Name: "+ fileName);
}
//mediaAdapter is providing support to play other file formats
else if(audioType.equalsIgnoreCase("vlc")
|| audioType.equalsIgnoreCase("mp4")){
mediaAdapter = new MediaAdapter(audioType);
mediaAdapter.play(audioType, fileName);
}
else{
System.out.println("Invalid media. "+
audioType + " format not supported");
}
}
}
public class AdapterDemo{ //demo
public static void main(String[] args) {
AudioPlayer audioPlayer = new AudioPlayer();
audioPlayer.play("mp3", "beyond the horizon.mp3");
audioPlayer.play("mp4", "alone.mp4");
audioPlayer.play("vlc", "far far away.vlc");
audioPlayer.play("avi", "mind me.avi");
}
}
- MVC new StudentController(new Student(), StudentView());
class Student {
private String rollNo;
private String name;
public String getRollNo() {
return rollNo;
}
public void setRollNo(String rollNo) {
this.rollNo = rollNo;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
class StudentView {
public void printStudentDetails(String studentName, String studentRollNo){
System.out.println("Student: ");
System.out.println("Name: " + studentName);
System.out.println("Roll No: " + studentRollNo);
}
}
public class StudentController {
private Student model;
private StudentView view;
public StudentController(Student model, StudentView view){
this.model = model;
this.view = view;
}
public void setStudentName(String name){
model.setName(name);
}
public String getStudentName(){
return model.getName();
}
public void setStudentRollNo(String rollNo){
model.setRollNo(rollNo);
}
public String getStudentRollNo(){
return model.getRollNo();
}
public void updateView(){
view.printStudentDetails(model.getName(), model.getRollNo());
}
}
public class MVCPatternDemo {
public static void main(String[] args) {
//fetch student record based on his roll no from the database
Student model = retriveStudentFromDatabase();
//Create a view : to write student details on console
StudentView view = new StudentView();
StudentController controller = new StudentController(model, view);
controller.updateView();
//update model data
controller.setStudentName("John");
controller.updateView();
}
private static Student retriveStudentFromDatabase(){
Student student = new Student();
student.setName("Robert");
student.setRollNo("10");
return student;
}
}
- Observer new OctalObserver(sub=new Subject());sub.update();
import java.util.ArrayList;
import java.util.List;
class Subject {
private List<Observer> observers
= new ArrayList<Observer>();
private int state;
public int getState() {
return state;
}
public void setState(int state) {
this.state = state;
System.out.println("setstatus in Subject");
notifyAllObservers();
}
public void attach(Observer observer){
observers.add(observer);
}
public void notifyAllObservers(){
for (Observer observer : observers) {
observer.update();
}
}
}
abstract class Observer {
protected Subject subject;
public abstract void update();
}
class BinaryObserver extends Observer{ //1
public BinaryObserver(Subject subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println( "update in Binaryparty: "
+ Integer.toBinaryString( subject.getState() ) );
}
}
class OctalObserver extends Observer{ //2
public OctalObserver(Subject subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println( "update in Octal String: "
+ Integer.toOctalString( subject.getState() ) );
}
}
public class ObserverDemo {
public static void main(String[] args) {
Subject subject = new Subject();
new OctalObserver(subject);
new BinaryObserver(subject);
subject.setState(15);
}
}
- strategy new Context(new OperationAdd()).context.executeStrategy(10, 5);
interface Strategy {
public int doOperation(int num1, int num2);
}
class OperationAdd implements Strategy{
@Override
public int doOperation(int num1, int num2) {
return num1 + num2;
}
}
class OperationSubstract implements Strategy{
@Override
public int doOperation(int num1, int num2) {
return num1 - num2;
}
}
class Context {
private Strategy strategy;
public Context(Strategy strategy){
this.strategy = strategy;
}
public int executeStrategy(int num1, int num2){
return strategy.doOperation(num1, num2);
}
}
public class StrategyDemo {
public static void main(String[] args) {
Context context = new Context(new OperationAdd());
System.out.println("10 + 5 = " + context.executeStrategy(10, 5));
context = new Context(new OperationSubstract());
System.out.println("10 - 5 = " + context.executeStrategy(10, 5));
}
}
8). Template new Football().play();
abstract class Game {
abstract void initialize();
abstract void startPlay();
abstract void endPlay();
//template method
public final void play(){
//initialize the game
initialize();
//start game
startPlay();
//end game
endPlay();
}
}
class Cricket extends Game {
@Override
void endPlay() {
System.out.println("Cricket Game Finished!");
}
@Override
void initialize() {
System.out.println("Cricket Game Initialized! Start playing.");
}
@Override
void startPlay() {
System.out.println("Cricket Game Started. Enjoy the game!");
}
}
class Football extends Game {
@Override
void endPlay() {
System.out.println("Football Game Finished!");
}
@Override
void initialize() {
System.out.println("Football Game Initialized! Start playing.");
}
@Override
void startPlay() {
System.out.println("Football Game Started. Enjoy the game!");
}
}
public class TemplateDemo {
public static void main(String[] args) {
Game game = new Cricket();
game.play();
System.out.println();
game = new Football();
game.play();
}
}
- Bridge new Circle(100,100, 10, new RedCircle()).draw();
interface DrawAPI {
public void drawCircle(int radius, int x, int y);
}
class RedCircle implements DrawAPI {
@Override
public void drawCircle(int radius, int x, int y) {
System.out.println("Drawing Circle[ color: red, radius: "
+ radius +", x: " +x+", "+ y +"]");
}
}
class GreenCircle implements DrawAPI {
@Override
public void drawCircle(int radius, int x, int y) {
System.out.println("Drawing Circle[ color: green, radius: "
+ radius +", x: " +x+", "+ y +"]");
}
}
abstract class Shape {
protected DrawAPI drawAPI;
protected Shape(DrawAPI drawAPI){
this.drawAPI = drawAPI;
}
public abstract void draw();
}
class Circle extends Shape {
private int x, y, radius;
public Circle(int x, int y, int radius, DrawAPI drawAPI) {
super(drawAPI);
this.x = x;
this.y = y;
this.radius = radius;
}
public void draw() {
drawAPI.drawCircle(radius,x,y);
}
}
public class BridgeDemo {
public static void main(String[] args) {
Shape redCircle = new Circle(100,100, 10, new RedCircle());
Shape greenCircle = new Circle(100,100, 10, new GreenCircle());
redCircle.draw();
greenCircle.draw();
}
}
- Decorator new RedShapeDecorator(new Circle()).draw()
interface Shape {
void draw();
}
class Rectangle implements Shape {//1
@Override
public void draw() {
System.out.println("Shape: Rectangle");
}
}
class Circle implements Shape {//1
@Override
public void draw() {
System.out.println("Shape: Circle");
}
}
abstract class ShapeDecorator implements Shape {//2
protected Shape decoratedShape;
public ShapeDecorator(Shape decoratedShape){
this.decoratedShape = decoratedShape;
}
public void draw(){
decoratedShape.draw();
}
}
class RedShapeDecorator extends ShapeDecorator {//2
public RedShapeDecorator(Shape decoratedShape) {
super(decoratedShape);
}
@Override
public void draw() {
decoratedShape.draw();
setRedBorder(decoratedShape);
}
private void setRedBorder(Shape decoratedShape){
System.out.println("Border Color: Red");
}
}
public class DecorationDemo {
public static void main(String[] args) {
Shape circle = new Circle();
Shape redCircle = new RedShapeDecorator(new Circle());
Shape redRectangle = new RedShapeDecorator(new Rectangle());
System.out.println("Circle with normal border");
circle.draw();
System.out.println("\nCircle of red border");
redCircle.draw();
System.out.println("\nRectangle of red border");
redRectangle.draw();
}
}
- Visitor new Computer().accept(new ComputerPartDisplayVisitor());
interface ComputerPart {
public void accept(ComputerPartVisitor computerPartVisitor);
}
class Keyboard implements ComputerPart {
@Override
public void accept(ComputerPartVisitor computerPartVisitor) {
computerPartVisitor.visit(this);
}
}
class Monitor implements ComputerPart {
@Override
public void accept(ComputerPartVisitor computerPartVisitor) {
computerPartVisitor.visit(this);
}
}
class Computer implements ComputerPart {
ComputerPart[] parts;
public Computer(){
parts = new ComputerPart[] {new Keyboard(), new Monitor()};
}
@Override
public void accept(ComputerPartVisitor computerPartVisitor) {
for (int i = 0; i < parts.length; i++) {
parts[i].accept(computerPartVisitor);
}
computerPartVisitor.visit(this);
}
}
interface ComputerPartVisitor {
public void visit(Computer computer);
public void visit(Keyboard keyboard);
public void visit(Monitor monitor);
}
class ComputerPartDisplayVisitor implements ComputerPartVisitor {
@Override
public void visit(Computer computer) {
System.out.println("Displaying Computer.");
}
@Override
public void visit(Keyboard keyboard) {
System.out.println("Displaying Keyboard.");
}
@Override
public void visit(Monitor monitor) {
System.out.println("Displaying Monitor.");
}
}
public class VisitorDemo{
public static void main(String[] args) {
ComputerPart computer = new Computer();
computer.accept(new ComputerPartDisplayVisitor());
}
}