深入淺出設(shè)計(jì)模式之命令模式

命令模式封裝調(diào)用一個(gè)例子publicvoidactionPerformed(ActionEvente){ Objectobj=e.getSource(); if(obj==mnuOpen)fileOpen();//openfile if(obj==mnuExit)exitClicked();//exitfromprogram if(obj==btnRed)redClicked();//turnred}privatevoidexitClicked(){System.exit(0);}privatevoidfileOpen(){ FileDialogfDlg=newFileDialog(this,"Openafile",FileDialog.LOAD); fDlg.show();}privatevoidredClicked(){ p.setBackground(Color.red);}上述程序設(shè)計(jì)，當(dāng)按鈕和菜單項(xiàng)不多的時(shí)候工作良好，但按鈕和菜單項(xiàng)多時(shí)，就不好辦了。publicinterfaceCommand{ publicvoidExecute();}publicvoidactionPerformed(ActionEvente){ Commandcmd=(Command)e.getSource(); cmd.Execute();}這樣，我們需要給每一個(gè)對(duì)象提供一個(gè)執(zhí)行的方法。命令模式theseprogramobjectsshouldbecompletelyseparatefromeachotherandshouldnothavetoknowhowotherobjectswork.TheuserinterfacereceivesacommandandtellsaCommandobjecttocarryoutwhateverdutiesithasbeeninstructedtodo.TheUIdoesnotandshouldnotneedtoknowwhattaskswillbeexecuted.命令模式程序?qū)ο髴?yīng)該徹底的彼此解耦，不需要知道其他的對(duì)象是如何工作的。用戶界面接收到命令然后告訴命令對(duì)象執(zhí)行設(shè)定的工作，用戶界面不知道也不應(yīng)該知道命令是如何執(zhí)行的。命令的發(fā)送者命令的接受者命令對(duì)象解耦了命令的發(fā)送者和命令的接受者飯店用餐顧客點(diǎn)了飯菜，形成一個(gè)訂單，侍者將訂單交給廚房，廚房根據(jù)訂單配菜。侍者無(wú)需知道訂單的內(nèi)容。飯菜的制作者和飯菜的消費(fèi)者完全分開，彼此無(wú)需直接聯(lián)系。遙控器的例子遙控器需要控制每一個(gè)電器的動(dòng)作，如電燈，電扇，電視機(jī)，同是開，動(dòng)作不一樣。我們?cè)O(shè)置命令接口

publicinterfaceCommand{publicvoidexecute();}publicclassLightOnCommandimplementsCommand{ Lightlight; publicLightOnCommand(Lightlight){ this.light=light; } publicvoidexecute(){ light.on(); }}命令的接收對(duì)象命令接收對(duì)象自己執(zhí)行命令對(duì)象接收對(duì)象實(shí)現(xiàn)了命令接口execute（）{receive.action();}

接受者CommandpublicclassSimpleRemoteControl{ Commandslot; publicSimpleRemoteControl(){}

publicvoidsetCommand(Commandcommand){ slot=command; }publicvoidbuttonWasPressed(){ slot.execute(); }}遙控器測(cè)試publicclassRemoteControlTest{ publicstaticvoidmain(String[]args){ SimpleRemoteControlremote=newSimpleRemoteControl(); Lightlight=newLight(); LightOnCommandlightOn=newLightOnCommand(light); remote.setCommand(lightOn); remote.buttonWasPressed(); }}命令模式將請(qǐng)求封裝成對(duì)象，使用不同的請(qǐng)求、隊(duì)列或日志來參數(shù)化其他對(duì)象。命令模式支持可撤銷操作。將請(qǐng)求封裝成對(duì)象，什么對(duì)象？對(duì)象將接受者和動(dòng)作包在內(nèi)部，只有一個(gè)execute接口，外部調(diào)用這個(gè)接口，不知會(huì)進(jìn)行什么樣的操作。多功能遙控器需要控制多個(gè)設(shè)備，每一個(gè)設(shè)備都有開關(guān)按鈕需要一個(gè)命令組，來控制設(shè)備組：起居室燈，廚房燈，吊扇，車庫(kù)門，音響，等publicclassRemoteControl{ Command[]onCommands; Command[]offCommands;

publicRemoteControl(){ onCommands=newCommand[7]; offCommands=newCommand[7];

CommandnoCommand=newNoCommand(); for(inti=0;i<7;i++){ onCommands[i]=noCommand; offCommands[i]=noCommand; } }

publicvoidsetCommand(intslot,CommandonCommand,CommandoffCommand){ onCommands[slot]=onCommand; offCommands[slot]=offCommand; }publicvoidonButtonWasPushed(intslot){ onCommands[slot].execute(); } publicvoidoffButtonWasPushed(intslot){ offCommands[slot].execute(); }publicclassLightOffCommandimplementsCommand{

？？

}NoCommand它是一個(gè)空對(duì)象，稱監(jiān)視對(duì)象，避免了判斷

if(onCommand[slot]!=null)onCommand[slot].execute();撤銷命令有時(shí)應(yīng)該允許后悔，允許命令撤銷。publicinterfaceCommand{ publicvoidexecute(); publicvoidundo();}publicclassLightOffCommandimplementsCommand{ Lightlight;

publicLightOffCommand(Lightlight){ this.light=light; }

publicvoidexecute(){ light.off(); }

publicvoidundo(){ light.on(); }}使用撤銷命令的遙控器代碼測(cè)試代碼使用狀態(tài)實(shí)現(xiàn)撤銷吊扇代碼加入撤銷到吊扇的命令類代碼其它幾個(gè)low,medium,off.如何實(shí)現(xiàn)。測(cè)試吊扇類代碼遙控器的party模式產(chǎn)生一個(gè)新的命令，可以讓所有設(shè)備打開。publicclassMacroCommandimplementsCommand{ Command[]commands; publicMacroCommand(Command[]commands){ mands=commands; } publicvoidexecute(){ for(inti=0;i<commands.length;i++){ commands[i].execute(); } } publicvoidundo(){ for(inti=0;i<commands.length;i++){ commands