观察者模式-java

package u21;

import java.util.ArrayList;
public class Fen{
    private ArrayList<Guancha> oblist;
    public Fen(){
        oblist=new ArrayList<>();
    }
    public void add(Guancha a){
        oblist.add(a);
    }
    public void remove(Guancha a){
        oblist.remove(a);
    }
    public void sheng(double a){
        if(a>0.05)
            for(Guancha guan:oblist){
                    guan.sheng();
            }
    }
    public void jiang(double a){
        if(a>0.05)
            for(Guancha guan:oblist){
                    guan.jiang();
            }
    }
}

package u21;

public interface Guancha {
    public void sheng();
    public void jiang();
}

package u21;

public class Gumin implements Guancha{
    private String name;
    public Gumin(String a){name=a;}
    public void sheng(){
        System.out.println(name+"买了一些股票（股票升了）");
    }
    public void jiang(){
        System.out.println("股票降价了，哭了");
    }
}

package u21;

public class main {
    public static void main(String[] args) {
        Fen f=new Fen();
        Gumin g1=new Gumin("第一个股民");
        Gumin g2=new Gumin("第二个股民");
        f.add(g1);
        f.add(g2);
        System.out.println("股票升了");
        f.sheng(0.1);
        System.out.println("比率小于5%");
        System.out.println();
        f.sheng(0.001);

        System.out.println("股票降了");
        f.jiang(0.1);
        System.out.println("比率小于5%");
        System.out.println();
        f.jiang(0.001);
    }
}