Design Pattern
Factory Pattern
How to implement?
Strategy Pattern
How to implement?
Abstract Factory Pattern
Abstract Factory Pattern
Abstract Factory Pattern
Abstract Factory Pattern
Abstract Factory Pattern
Singleton Pattern
Singleton Pattern
Singleton Pattern
Template Pattern
Step 3
Use the Game's template method play() to demonstrate a defined way of playing game.
Observer Pattern
Situation
We have observers listen to a subject. When the subject has changed its state, all the observers will get updated.
Before
public class BinaryObserver extends Observer{
@Override
public void update(int state) {
System.out.println( "Binary String: " + Integer.toBinaryString( state ) );
}
}public class OctalObserver extends Observer{
@Override
public void update(int state) {
System.out.println( "Octal String: " + Integer.toOctalString( state ) );
}
}BinaryObserver.java
OctalObserver.java
public abstract class Observer {
public abstract void update(int state);
}Observer.java
Before
public class Subject {
private Observer binaryObserver = BinaryObserver();
private Observer octalObserver = OctalObserver();
private int state;
public void setState(int state) {
this.state = state;
notifyAllObservers();
}
public void notifyAllObservers(){
binaryObserver.update(this.state);
octalObserver.update(this.state);
}
}Subject.java
Before
public class ObserverPatternDemo {
public static void main(String[] args) {
Subject subject = new Subject();
System.out.println("First state change: 15");
subject.setState(15);
System.out.println("Second state change: 10");
subject.setState(10);
}
}ObserverPatternDemo.java
After
import java.util.ArrayList;
import java.util.List;
public 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;
notifyAllObservers();
}
public void attach(Observer observer){
observers.add(observer);
}
public void notifyAllObservers(){
for (Observer observer : observers) {
observer.update();
}
}
}Subject.java
After
public class BinaryObserver extends Observer{
public BinaryObserver(Subject subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println( "Binary String: " + Integer.toBinaryString( subject.getState() ) );
}
}public class OctalObserver extends Observer{
public OctalObserver(Subject subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println( "Octal String: " + Integer.toOctalString( subject.getState() ) );
}
}BinaryObserver.java
public abstract class Observer {
protected Subject subject;
public abstract void update();
}OctalObserver.java
Observer.java
After
public class ObserverPatternDemo {
public static void main(String[] args) {
Subject subject = new Subject();
new HexaObserver(subject);
new OctalObserver(subject);
new BinaryObserver(subject);
System.out.println("First state change: 15");
subject.setState(15);
System.out.println("Second state change: 10");
subject.setState(10);
}
}ObserverPatternDemo.java
Design Pattern
By shirlin1028
