浅谈JAVA设计模式之——观察者模式（Observer）

package com.lyz.design.observer;
import java.util.ArrayList;
import java.util.List;
/**
 * Subject 
 * @author binghe
 *
 */
public abstract class Citizen {
    List pols;
    String help = "normal";
    public void setHelp(String help) {
        this.help = help;
    }
    public String getHelp() {
        return this.help;
    }
    abstract void sendMessage(String help);
    public void setPolicemen() {
        this.pols = new ArrayList();
    }
    public void register(Policeman pol) {
        this.pols.add(pol);
    }
    public void unRegister(Policeman pol) {
        this.pols.remove(pol);
    }
}

package com.lyz.design.observer;
/**
 * Observer 
 * @author binghe
 *
 */
public interface Policeman {
    void action(Citizen ci);
}

package com.lyz.design.observer;
/**
 * ConcreteSubject 
 * @author binghe
 *
 */
public class HuangPuCitizen extends Citizen {
    public HuangPuCitizen(Policeman pol) {
        setPolicemen();
        register(pol);
    }
    public void sendMessage(String help) {
        setHelp(help);
        for(int i = 0; i < pols.size(); i++) {
            Policeman pol = pols.get(i);
            //通知警察行动
            pol.action(this);
        }
    }
}

package com.lyz.design.observer;
/**
 * ConcreteObserver 
 * @author binghe
 *
 */
public class HuangPuPoliceman implements Policeman {
    public void action(Citizen ci) {
        String help = ci.getHelp();
        if (help.equals("normal")) {
            System.out.println("一切正常, 不用出动");
        }
        if (help.equals("unnormal")) {
            System.out.println("有犯罪行为, 黄埔警察出动!");
        }
    }
}

package com.lyz.design.observer;
/**
 * ConcreteObserver 
 * @author binghe
 *
 */
public class TianHePoliceman implements Policeman {
    public void action(Citizen ci) {
        String help = ci.getHelp();
        if (help.equals("normal")) {
            System.out.println("一切正常, 不用出动");
        }
        if (help.equals("unnormal")) {
            System.out.println("有犯罪行为, 天河警察出动!");
        }
    }
}

package com.lyz.design.observer;
/**
 * Test 
 * @author binghe
 *
 */
public class Test{
    public static void main(String[] args) {
        Policeman thPol = new TianHePoliceman();
        Policeman hpPol = new HuangPuPoliceman();
        Citizen citizen = new HuangPuCitizen(hpPol);
        citizen.sendMessage("unnormal");
        citizen.sendMessage("normal");
        System.out.println("===========");
        citizen = new TianHeCitizen(thPol);
        citizen.sendMessage("normal");
        citizen.sendMessage("unnormal");
    }
}