设计
以下是可复用事件处理一文的原代码。目前，面向对象是软件系统建模的主流技术，使用面向对象技术建模的主要指标之一是可复用性。为了更好地解决软件复用性和扩展性问题，设计模式得到了越来越多的关注与应用。结合command设计模式和Java语言的反射技术，本文设计实现了一个可复用的事件处理框架。在面向对象的系统设计中，有些方面的可复用性经常被忽略了，用户界面（User Interface, 下文简称UI）及其事件处理就是其中之一。一个完整的UI设计应该包括两部分：UI及其相应的事件处理机制，没有事件处理机制的UI是没有用的，对于事件处理，也应该考虑可复用设计。虽然看上去有些奇怪，但是这种设计是有实用价值的――提高了代码的可复用性、健壮性和可维护性。command设计模式的主要设计思想是把对某一对象的请求封装为一个对象，从而把发出命令的责任和执行任务的责任分开，委派给不同的对象，请求的一方不必知道接收请求一方的接口。这种引入第三方类的做法是设计模式所惯用的，引入的第三方类解耦了紧耦合对象。command设计模式中，第三方类解耦了调用操作的对象与知道如何实现该操作的对象，提高了软件的可复用性。JDK 1.1及其以后的版本，引入了反射（reflection）技术。反射是Java中非常突出的动态特征，利用它可以加载一个运行时才得知名字的class，获取其完整结构，这一切是通过反射API完成的。//UIDemo1
import java.awt.*;
import java.awt.event.*;
import javax.swing.*; public class UIDemo1 implements ActionListener{
private JFrame frame;
private JButton button;
private JTextArea area;
private int index = -1;
private String [] params; private UIDemo1(String args[]){
params = args;
area = new JTextArea(5,25);
button = new JButton("Click here!");
button.addActionListener(this); frame = new JFrame(getClass().getName());
frame.addWindowListener(new ReusableWindowAdapter());
Container cont = frame.getContentPane();
JScrollPane scrollPane = new JScrollPane(area);
cont.add(scrollPane,BorderLayout.NORTH);
cont.add(button,BorderLayout.SOUTH);
frame.pack();
frame.setVisible(true);
} public void actionPerformed(ActionEvent ae){
//provide equality check to see if source was the
//button defined above.. useful only if we register
//this ActionListener with multiple sources
if(ae.getSource().equals(button)){
index = ++index % params.length;
area.setText(params[index]);
}
} public static void main(String args[]){
if(args.length > 1){
UIDemo1 one = new UIDemo1(args);
}else{
usage();
}
}
private static void usage(){
System.err.println("You may excute this program as below:");
System.err.println("java UIDemo1 params1 params2 ...");
System.exit(-1);
}
}//UIDemo2
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;public class UIDemo2{
private JFrame frame;
private JButton button;
private JTextArea area;
private int index = -1;
private String [] params; private UIDemo2(String args[]){
params = args;
area = new JTextArea(5,25);
button = new JButton("Click Here!");
button.addActionListener(new SemiReusableActionListener(this)); frame = new JFrame(getClass().getName());
frame.addWindowListener(new ReusableWindowAdapter());
Container cont = frame.getContentPane();
JScrollPane scrollPane = new JScrollPane(area);
cont.add(scrollPane,BorderLayout.NORTH);
cont.add(button,BorderLayout.SOUTH);
frame.pack();
frame.setVisible(true);
}
void setMessage(Object source){
if(source.equals(button)){
index = ++index % params.length;
area.setText(params[index]);
}
} public static void main(String args[]){
if(args.length > 1){
UIDemo2 two = new UIDemo2(args);
}else{
usage();
}
}
private static void usage(){
System.err.println("You may excute this program as below:");
System.err.println("java UIDemo2 params1 params2 ...");
System.exit(-1);
}
}//SemiReusableActionListenerimport java.awt.event.*;public class SemiReusableActionListener implements ActionListener{
private UIDemo2 demo2;
SemiReusableActionListener(UIDemo2 uiDemo){
demo2 = uiDemo;
}
public void actionPerformed(ActionEvent ae){
demo2.setMessage(ae.getSource());
}
}//UIDemo3
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.lang.reflect.*;public class UIDemo3{
private JFrame frame;
private JButton button1;
private JTextArea area;
private int index = -1;
private String [] params;
private UIDemo3(String args[]){
params = args;
area = new JTextArea(5,25);
button1 = new JButton("Click here!");
//setup required information to use GenericActionListener
String methodName = "setMessage";
Class [] paramTypes = {java.lang.Object.class};
Object [] methodArgs = { button1 };
Class clazz = this.getClass();
try{
Method method = clazz.getMethod(methodName, paramTypes); button1.addActionListener(new
ReusableActionListener(method, this, methodArgs));
}
catch(Exception e){
System.out.println("Could not find the method: "+methodName+"\nNow Exiting...");
System.exit(-1);
} frame = new JFrame(getClass().getName());
frame.addWindowListener(new ReusableWindowAdapter());
Container cont = frame.getContentPane();
JScrollPane scrollPane = new JScrollPane(area);
cont.add(scrollPane,BorderLayout.NORTH);
cont.add(button1,BorderLayout.SOUTH);
frame.pack();
frame.setVisible(true);
}
public void setMessage(Object source){
if(source.equals(button1)){
index = ++index % params.length;
area.setText(params[index]);
}
}
public static void main(String args[]){
if(args.length > 1){
UIDemo3 three = new UIDemo3(args);
}else{
usage();
}
}
private static void usage(){
System.err.println("You may excute this program as below:");
System.err.println("java UIDemo3 params1 params2 ...");
System.exit(-1);
}
}
//ReusableWindowAdapter import java.awt.*;
import java.awt.event.*;public class ReusableWindowAdapter extends WindowAdapter{
public void windowClosing(WindowEvent we){
Object source = we.getSource();
if(source instanceof Frame){
((Frame)source).setVisible(false);
((Frame)source).dispose();
System.exit(0);
}
}
}