[자바] Observer 패턴

 

'관찰자'

관찰하는 객체를 'Observer' 인터페이스를 구현하도록 하고,

관찰하려는 객체는 'Observable'을 상속한다.

 

다음예제는 난수를 만들고 이를 'Observer'가 관찰하고, 그 수를 출력하도록 한다.

 

package observer;

public interface Observer {
	public void update(NumberGenerator generator);
}

package observer;

import java.util.ArrayList;
import java.util.Iterator;

public abstract class NumberGenerator {
	private ArrayList<Observer> observers = new ArrayList<Observer>();
	
	public void addObserver(Observer observer) {
		observers.add(observer);
	}
	
	public void deleteObserver(Observer observer) {
		observers.remove(observer);
	}
	
	public void notifyObservers() {
		Iterator<Observer> obsItr = observers.iterator();
		while(obsItr.hasNext()) {
			Observer o = obsItr.next();
			o.update(this);
		}
	}
	
	public abstract int getNumber();
	public abstract void execute();
}

package observer;

import java.util.Random;

public class RandomNumberGenerator extends NumberGenerator {
	private Random random = new Random();
	private int number;
	
	@Override
	public int getNumber() {
		return number;
	}

	@Override
	public void execute() {
		for (int i = 0; i < 20; i++) {
			number = random.nextInt(50);
			notifyObservers();
		}
	}

}

package observer;

/**
 * 관찰한 수를 '숫자'로 표시하기 위함.
 * @author dev-jones
 *
 */
public class DigitObserver implements Observer {

	@Override
	public void update(NumberGenerator generator) {
		System.out.println("DigitObserver : " + generator.getNumber());
		try {
			Thread.sleep(1000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}

package observer;

public class GraphObserver implements Observer {

	@Override
	public void update(NumberGenerator generator) {
		System.out.print("GraphObserver :");
		int count = generator.getNumber();
		for (int i = 0; i < count; i++) {
			System.out.print("*");
		}
		System.out.println();
		try {
			Thread.sleep(1000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}

package observer;

public class Main {

	public static void main(String[] args) {
		NumberGenerator generator = new RandomNumberGenerator();
		Observer observer1 = new DigitObserver();
		Observer observer2 = new GraphObserver();
		
		generator.addObserver(observer1);
		generator.addObserver(observer2);
		generator.execute();
	}
}

실행결과:

DigitObserver : 37
GraphObserver :*************************************
DigitObserver : 32
GraphObserver :********************************
DigitObserver : 27
GraphObserver :***************************
DigitObserver : 12
GraphObserver :************
DigitObserver : 20
GraphObserver :********************
DigitObserver : 25
GraphObserver :*************************
DigitObserver : 46
GraphObserver :**********************************************
DigitObserver : 30
GraphObserver :******************************
DigitObserver : 15
GraphObserver :***************
DigitObserver : 44
GraphObserver :********************************************
DigitObserver : 32
GraphObserver :********************************
DigitObserver : 30
GraphObserver :******************************
DigitObserver : 16
GraphObserver :****************
DigitObserver : 20
GraphObserver :********************
DigitObserver : 24
GraphObserver :************************
DigitObserver : 12
GraphObserver :************
DigitObserver : 45
GraphObserver :*********************************************
DigitObserver : 0
GraphObserver :
DigitObserver : 3
GraphObserver :***
DigitObserver : 6
GraphObserver :******