package Test;

public class Clinet {
    public static void main(String[] args) {
        IntervalWindow Iw= new IntervalWindow();
        Interval i=new Interval();
        i.addObserver(Iw);
    }
}

package Test;

import java.util.Observable;

public class Interval extends Observable {
    public String start = "0";
    public String end = "0";
    public String length = "0";

    public void calculatestart(String start, String end) {
        this.start = start;
        this.end = end;
        this.length = String.valueOf(Integer.parseInt(start)
                - Integer.parseInt(end));
        setChanged();
        notifyObservers();
    }


    public void calculateend(String start, String end) {
        this.start = start;
        this.end = end;
        this.length = String.valueOf(Integer.parseInt(start)
                - Integer.parseInt(end));
        setChanged();
        notifyObservers();
    }

    public void calculatelength(String start, String length) {
        this.start = start;
        this.length = length;
        this.end = String.valueOf(Integer.parseInt(start)
                - Integer.parseInt(length));
        setChanged();
        notifyObservers();
    }
    
    
}

package Test;

import java.awt.Color;
import java.awt.GridLayout;
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;
import java.util.Observable;
import java.util.Observer;

import javax.swing.JFrame;
import javax.swing.JTextField;

@SuppressWarnings("serial")
public class IntervalWindow extends JFrame implements Observer {
    JTextField start = new JTextField("0", 10);
    JTextField end = new JTextField("0", 10);
    JTextField length = new JTextField("0", 10);
    GridLayout fl = new GridLayout(3, 1);

    public IntervalWindow() {
        super("测试观察者模式在GUI中的使用");
        this.setSize(400, 400);
        this.setLocation(500, 100);
        this.setBackground(Color.WHITE);

        this.setLayout(fl);

        this.add(start);
        this.add(end);
        this.add(length);
        start.addFocusListener(new SymFocus());
        end.addFocusListener(new SymFocus());
        length.addFocusListener(new SymFocus());
        this.setVisible(true);
    }

    class SymFocus extends FocusAdapter {

        private String tf_start;
        private String tf_end;
        private String tf_length;
        private Interval interval = new Interval();

        @Override
        public void focusLost(FocusEvent event) {
            Object obj = event.getSource();
            if (obj == start) {
                tf_start = start.getText();
                tf_end = end.getText();
                interval.calculatestart(tf_start, tf_end);
            } else if (obj == end) {
                tf_start = start.getText();
                tf_end = end.getText();
                interval.calculateend(tf_start, tf_end);
            } else if (obj == length) {
                tf_start = start.getText();
                tf_length = length.getText();
                interval.calculatelength(tf_start, tf_length);
            }

        }

    }

    @Override
    public void update(Observable o, Object arg1) {
        System.out.println("her");
        start.setText(((Interval) o).start);
        end.setText(((Interval) o).end);
        length.setText(((Interval) o).length);
    }

}