命令模式定義:將請求,命令,動作等封裝成對象,這樣可以讓項目使用這些對象來參數化其他對象。是的命令的請求者和執行者解耦。
以下是一個遙控器的例子,如果按照傳統OO思想,我們一般會直接讓遙控器去調用硬件提供的API,但是這種寫法,會導致遙控器與特定的硬件API強耦合。當我們的需要接入新的設備,修改按鈕所綁定硬件命令,這時候就會相當不便。我們有個準則是,原來已經測試好的代碼,儘量不去改動。而使用命令模式就可以達到這個效果。將命令抽象成接口,所有硬件命令實現該接口,當需要調用某個硬件api,就直接調用接口的api,這樣就可以實現控制器與硬件的解耦。
代碼示例如下:
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//命令接口 public interface Command
{ //執行命令 public void execute(); //回退命令 public void undo(); } |
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public class LightOffCommand implements Command
{ private String
name; public LightOffCommand(String
name) { super (); this .name
= name; } @Override public void execute()
{ System.out.println( "關閉--" +name+ "--的燈" ); } @Override public void undo()
{ System.out.println( "打開--" +name+ "--的燈" ); } } |
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public class LightOnCommand implements Command
{ private String
name; public LightOnCommand(String
name) { super (); this .name
= name; } @Override public void execute()
{ System.out.println( "打開--" +name+ "--的燈" ); } @Override public void undo()
{ System.out.println( "關閉--" +name+ "--的燈" ); } } |
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//空命令類的作用是,防止初始化的按鈕,沒有綁定導致空指針異常 public class NoCommand implements Command
{ @Override public void execute()
{ System.out.println( "沒有綁定任何電器,所以無反應" ); } @Override public void undo()
{ //
TODO Auto-generated method stub } } |
控制器類:
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//遙控器App對象 public class TeleController
{ private NoCommand
noCommand = new NoCommand(); //初始遙控器只有三對命令 private List<Command>
leftButtonList; private List<Command>
rightButtonList; //遙控器操作記錄 private Stack<Command>
records = new Stack<Command>(); public TeleController(){ leftButtonList
= new ArrayList<Command>( 3 ); rightButtonList
= new ArrayList<Command>( 3 ); leftButtonList.add(noCommand); leftButtonList.add(noCommand); leftButtonList.add(noCommand); rightButtonList.add(noCommand); rightButtonList.add(noCommand); rightButtonList.add(noCommand); } public void clickButton( int index, boolean left){ if (left){ leftButtonList.get(index).execute(); records.push(leftButtonList.get(index)); } else { rightButtonList.get(index).execute(); records.push(rightButtonList.get(index)); } } public void backButton(){ if (!records.isEmpty()){ records.pop().undo(); } else { System.out.println( "已無更多操作記錄,回退失敗" ); } } public void setCommand( int index, boolean left,
Command command){ if (left){ leftButtonList.set(index,
command); } else { rightButtonList.set(index,
command); } } public void addButton( boolean left){ if (left){ leftButtonList.add(noCommand); } else { rightButtonList.add(noCommand); } } } |
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//掃地機器人---邏輯相同,可跳過該代碼 public class RoombaOnCommand implements Command
{ @Override public void execute()
{ System.out.println( "掃地機器人--開始--打掃" ); } @Override public void undo()
{ System.out.println( "掃地機器人--停止--打掃" ); } } |
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public class RoombaOffCommand implements Command
{ @Override public void execute()
{ System.out.println( "掃地機器人--停止--打掃" ); } @Override public void undo()
{ System.out.println( "掃地機器人--開始--打掃" ); } } |
主測試函數:
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public class Main
{ private static final boolean leftButton
= true ; private static final boolean rightButton
= false ; public static void main(String[]
args) { TeleController
teleController = new TeleController(); teleController.clickButton( 0 ,
leftButton); System.out.println( "左邊第一欄按鈕綁定臥室燈【開啓】命令" ); teleController.setCommand( 0 ,
leftButton, new LightOnCommand( "臥室燈" )); System.out.println( "右邊第一欄按鈕綁定臥室燈【關閉】命令" ); teleController.setCommand( 0 ,
rightButton, new LightOffCommand( "臥室燈" )); System.out.println( "左邊第二欄按鈕綁定打掃機器人【開啓】命令" ); teleController.setCommand( 1 ,
leftButton, new RoombaOnCommand()); System.out.println( "右邊第二欄按鈕綁定打掃機器人【關閉】命令" ); teleController.setCommand( 1 ,
rightButton, new RoombaOffCommand()); System.out.println( "按下左邊第一個按鈕" ); teleController.clickButton( 0 ,
leftButton); System.out.println( "按下左邊第二個按鈕" ); teleController.clickButton( 1 ,
leftButton); System.out.println( "按下回退按鈕" ); teleController.backButton(); System.out.println( "再按下回退按鈕" ); teleController.backButton(); System.out.println( "再按下回退按鈕" ); teleController.backButton(); } }
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