"JAVA Design Patterns" Observer Pattern

package cn.com.My;
//observer
public interface Obeserver {
		void update(String data);
}

package cn.com.My;
//leader
public interface Subject {
		void addObserver(Obeserver o);
		void removeObserver(Obeserver o);
		void notifyObserver();
}

package cn.com.My;

import com.wang.observer.TeacherSubject;

public class Student implements Obeserver{
	 private Teacher t;
	    //The name of the student, used to identify different student objects
	 private String name;
	public  Student(String name,Teacher  t) {
        this.name=name;
        this.t = t;
        //Each new student object is added to the observer's ranks by default
        t.addObserver(this);
    }
	@Override
	public void update(String data) {
		// TODO Auto-generated method stub
		   System.out.println(name+"Get job:"+data);
	}

}

package cn.com.My;

import java.util.ArrayList;
import java.util.List;

import javax.swing.JOptionPane;

public class Teacher implements Subject{
	private Obeserver o;
	private String str;
	List<Obeserver> list = new ArrayList<Obeserver>();
	public void addObserver(Obeserver o) {
		// TODO Auto-generated method stub
		this.o = o;
		list.add(o);
	}

	@Override
	public void removeObserver(Obeserver o) {
		// TODO Auto-generated method stub
		if(list.size() > 0){
			list.remove(list.indexOf(o));
		}else{
			System.out.println("No more...");
		}
	}

	@Override
	public void notifyObserver() {
		// TODO Auto-generated method stub
		for(int i = 0 ; i < list.size();i++){
			Obeserver o = list.get(i);
			o.update(str);
		}
	}
	
	public void setWork(String str){
		this.str = str;
		System.out.println("Today's homework is "+str);
		this.notifyObserver();
	}

}