Command—俺有一个mm家里管得特别严，没法见面，只好借助于她弟弟在我们俩之间
传送信息，她对我有什么指示，就写一张纸条让她弟弟带给我。这不，她弟弟又传送过来
一个command，为了感谢他，我请他吃了碗杂酱面，哪知道他说：“我同时给我姐姐三个
男朋友送command，就数你最小气，才请我吃面。”，
命令模式：命令模式把一个请求或者操作封装到一个对象中。命令模式把发出命令的责任
和执行命令的责任分割开，委派给不同的对象。命令模式允许请求的一方和发送的一方独
立开来，使得请求的一方不必知道接收请求的一方的接口，更不必知道请求是怎么被接收
，以及操作是否执行，何时被执行以及是怎么被执行的。系统支持命令的撤消。
这是Command模式的UML图
pre {font-family:"Courier New", Courier, Arial; font-size: 12px;} .operator {color: #000000;} .keyword {color: #993300;} .identifier {color: #000087;} .properties {color: #000087;} .identifier2 {color : #000087;} .linecomment, .blockcomment {color: #808080;} .string {color: #0000FF;}
class Command { private function Command() { } // Methods public function Execute():Void { } public function UnExecute():Void { } } // "ConcreteCommand" class CalculatorCommand extends Command { // Fields private var $operator:String; private var operand:Number; private var calculator:Calculator; // Constructor public function CalculatorCommand(calculator:Calculator, $operator:String, operand:Number) { this.calculator = calculator; this.$operator = $operator; this.operand = operand; } // Properties public function set Operator(value:String):Void { $operator = value; } public function set Operand(value:Number):Void { operand = value; } // Methods public function Execute():Void { calculator.Operation($operator, operand); } public function UnExecute():Void { calculator.Operation(Undo($operator), operand); } // Private helper function private function Undo($operator:String):String { var undo:String =""; switch ($operator) { case "+" : undo = "-"; break; case "-" : undo = "+"; break; case "*" : undo = "/"; break; case "/" : undo = "*"; break; } return undo; } } // "Receiver" class Calculator { // Fields private var total:Number = 0; // Methods public function Operation($operator:String, operand:Number):Void { switch ($operator) { case "+" : total += operand; break; case "-" : total -= operand; break; case "*" : total *= operand; break; case "/" : total /= operand; break; } trace("Total =" + total + " (following" + $operator + " " + operand + ")"); } } // "Invoker" class User { // Fields private var calculator:Calculator; private var commands:Array = new Array(); private var current:Number = 0; public function User() { calculator = new Calculator(); } // Methods public function Redo(levels:Number):Void { //trace(commands[current++] instanceof Command); trace("---- Redo " + levels + " levels "); // Perform redo operations for (var i = 0; i < levels; i++) { if (current < commands.length - 1) { commands[current++].Execute(); } } } public function Undo(levels:Number):Void { trace("---- Undo" + levels + " levels "); // Perform undo operations for (var i = 0; i < levels; i++) { if (current > 0) { commands[--current].UnExecute(); } } } public function Compute($operator:String, operand:Number):Void { // Create command operation and execute it var command:Command = new CalculatorCommand(calculator, $operator, operand); command.Execute(); // Add command to undo list commands.push(command); current++; } } client.fla // Create user and let her compute var user:User = new User(); user.Compute('+', 100); user.Compute('-', 50); user.Compute('*', 10); user.Compute('/', 2); // Undo and then redo some commands user.Undo(4); user.Redo(3);
output:
Total =100 (following+ 100)
Total =50 (following- 50)
Total =500 (following* 10)
Total =250 (following/ 2)
---- Undo4 levels
Total =500 (following* 2)
Total =50 (following/ 10)
Total =100 (following+ 50)
Total =0 (following- 100)
---- Redo 3 levels
Total =100 (following+ 100)
Total =50 (following- 50)
Total =500 (following* 10)
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