《重构，改善现有代码的设计》第八章 Duplicate Observed Data

Java代码

import java.awt.Color;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.Label;
import java.awt.TextField;
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.util.Observable;
import java.util.Observer;

import javax.swing.JFrame;

/**
* 《重构，改善现有代码的设计》第八章 Duplicate Observed Data
*
* 业务逻辑：
* 一个JFrame（类IntervalWindow）有三个TextField，分别是start,end和length
* 如果你修改Start或End，length就会自动成为两者计算所得的长度
* 如果你修改length，End就会随之改变(start不变)
*
* 主要是使用了Observer模式：
* start,end和length之间的运算，是与具体界面无关的，应该独立出来（成为一个Subject，观察者模式里面的“目标”）
*
* 关键在于解决以下两个问题：
* 1.什么时候计算？当界面上的TextField值有变动时，由WindowObserver调用Subject的set方法
* 2.计算后如何通知界面？Subject调用notifyObservers方法，这个方法会触发WindowObserver的update方法
*
*/
public class ObserveGUIWindow {
public static 
void main(String[] args) {
new WindowObserver().init();
}
}

class WindowObserver implements Observer {

private TextField startField;
private TextField endField;
private TextField lengthField;
private Subject subject;

public void init() {
JFrame f = new JFrame("This is a test");
f.setSize(200, 200);
Container content = f.getContentPane();
content.setBackground(Color.white);
content.setLayout(new FlowLayout());

startField = new TextField("0",
10);
endField = new TextField("0",
10);
lengthField = new TextField("0",
10);
SymFocus listener = new SymFocus();
startField.addFocusListener(listener);
endField.addFocusListener(listener);
lengthField.addFocusListener(listener);

Label startLabel = new Label("start:");
Label endLabel = new Label("end:");
Label lengthLabel = new Label("length:");
content.add(startLabel);
content.add(startField);
content.add(endLabel);
content.add(endField);
content.add(lengthLabel);
content.add(lengthField);

f.setLocationRelativeTo(null);
f.setVisible(true);

f.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});

subject = new Subject();
subject.addObserver(this);

}

//更新界面，最新的值(计算后)来自Subject
public void update(Observable o, Object arg) {
Subject subject = (Subject)o;
startField.setText(subject.getStart());
endField.setText(subject.getEnd());
lengthField.setText(subject.getLength());
}

class SymFocus extends FocusAdapter {
public void focusLost(FocusEvent event) {
Object object = event.getSource();
if (object == startField)
StartFieldFocusLost(event);
else if (object == endField)
EndFieldFocusLost(event);
else if (object == lengthField)
LengthFieldFocusLost(event);
}
}

void StartFieldFocusLost(FocusEvent event) {

//从界面取得输入的值
String start = startField.getText();
subject.setStart(isInteger(start) ? start : "0");

//交由Subject计算
subject.calculateLength();
}

void EndFieldFocusLost(FocusEvent event) {
String end = endField.getText();
subject.setEnd(isInteger(end) ? end : "0");
subject.calculateLength();
}

void LengthFieldFocusLost(FocusEvent event) {
String length = lengthField.getText();
subject.setLength(isInteger(length) ? length : "0");
subject.calculateEnd();
}

boolean isInteger(String str) {
return str != null && str.matches("[0-9]+");
}

}