単純なプログラムを書換えよう（Java編）−Applet
ObserverとCommandとSingletonを使ったプログラムをAppletにしてみました．手を入れたのはView.javaとController.javaで，それ以外は修正不要です．また，Appletなのでmain関数を記述したMain.javaはファイル自体が不要です．
//View.java import java.applet.Applet; import java.awt.*; import java.util.Observer; import java.util.Observable; public class View extends Applet implements Observer{ private Label value=new Label(); public void init(){ Model model=new Model(); Controller controller=new Controller(model); setLayout(new BorderLayout()); Panel buttons=new Panel(); Button inc=new Button("inc"); Button dec=new Button("dec"); buttons.add(inc); buttons.add(dec); inc.addActionListener(controller); dec.addActionListener(controller); add(buttons,BorderLayout.SOUTH); add(value,BorderLayout.CENTER); model.addObserver((Observer)this); model.setValue(model.getValue()); } public void update(Observable obs,Object obj){ value.setText(Integer.toString(((Model)obs).getValue())); } } //end //Controller.java import java.awt.event.ActionEvent; import java.awt.event.ActionListener; public class Controller implements ActionListener{ private Model model; private CommandDispatcher commandDispatcher=CommandDispatcher.getInstance(); public Controller(Model model){ this.model=model; } public void actionPerformed(ActionEvent actionEvent){ commandDispatcher.getCommand(actionEvent.getActionCommand()).execute(model); } } //end //Model.java import java.util.Observable; public class Model extends Observable{ private int value; public Model(){ this(0); } public Model(int value){ setValue(value); } public final int getValue(){ return value; } public final void setValue(int value){ this.value=value; setChanged(); notifyObservers(); } public int inc(){ return inc(1); } public int inc(int value){ setValue(getValue()+value); return getValue(); } public int dec(){ return dec(1); } public int dec(int value){ setValue(getValue()-value); return getValue(); } } //end //Command.java public interface Command{ void execute(Object o); } //end //IncCommand.java public class IncCommand implements Command{ public void execute(Object model){ ((Model)model).inc(); } } //end //DecCommand.java public class DecCommand implements Command{ public void execute(Object model){ ((Model)model).dec(); } } //end //CommandDispatcher.java import java.util.Map; import java.util.HashMap; public class CommandDispatcher{ private static Map commands=new HashMap(); private static CommandDispatcher commandDispatcher=new CommandDispatcher(); static{ commands.put("inc","IncCommand"); commands.put("dec","DecCommand"); } private CommandDispatcher(){ } public static CommandDispatcher getInstance(){ return commandDispatcher; } public Command getCommand(String command){ Command executeCommand=null; try{ executeCommand=(Command)Class.forName(commands.get(command).toString()).newInstance(); } catch(ClassNotFoundException e){ e.printStackTrace(); } catch(InstantiationException e){ e.printStackTrace(); } catch(IllegalAccessException e){ e.printStackTrace(); } finally{ return executeCommand; } } } //end
appletviewerで表示させるため，以下のhtmlファイル(view.html)も作成しました．
<html> <body> <object code="View.class" width="100" height="100"></object> </body> </html>