命令模式

1.定义

将一个请求封装成一个对象，从而让用户使用不同的请求把客户端参数化；对请求排队或者记录请求日志，以及支持可撤销的操作。

2.实现（俄罗斯方块）

/** * 俄罗斯方块操作的真正逻辑代码(左移，右移，快速落下，改变形状) */ public class RealOperation { public void toLeft(){ System.out.println("toLeft"); } public void toRight(){ System.out.println("toRight"); } public void fastToBottom(){ System.out.println("fastToBottom"); } public void transForm(){ System.out.println("transForm"); } } /** * 命令的抽象，便于实现四个具体的命令 */ public interface Command { public void execute(); } /** * 左移的具体实现 */ public class LeftCommand implements Command { private RealOperation operation; public LeftCommand(RealOperation operation) { this.operation = operation; } @Override public void execute() { operation.toLeft(); } } /** * 右移的具体实现 */ public class RightCommand implements Command { private RealOperation operation; public RightCommand(RealOperation operation) { this.operation = operation; } @Override public void execute() { operation.toRight(); } } /** * 快速落下的具体实现 */ public class FallCommand implements Command { private RealOperation operation; public FallCommand(RealOperation operation) { this.operation = operation; } @Override public void execute() { operation.fastToBottom(); } } /** * 改变形状的具体实现 */ public class TransFormCommand implements Command { private RealOperation operation; public TransFormCommand(RealOperation operation) { this.operation = operation; } @Override public void execute() { operation.transForm(); } } /** * 四个命令的管理者 */ public class Commander { private LeftCommand leftCommand; private RightCommand rightCommand; private FallCommand fallCommand; private TransFormCommand transFormCommand; public LeftCommand getLeftCommand() { return leftCommand; } public void setLeftCommand(LeftCommand leftCommand) { this.leftCommand = leftCommand; } public RightCommand getRightCommand() { return rightCommand; } public void setRightCommand(RightCommand rightCommand) { this.rightCommand = rightCommand; } public FallCommand getFallCommand() { return fallCommand; } public void setFallCommand(FallCommand fallCommand) { this.fallCommand = fallCommand; } public TransFormCommand getTransFormCommand() { return transFormCommand; } public void setTransFormCommand(TransFormCommand transFormCommand) { this.transFormCommand = transFormCommand; } //调用具体实现方法实现命令 public void toLeft(){ leftCommand.execute(); } public void toRight(){ rightCommand.execute(); } public void fall(){ fallCommand.execute(); } public void transForm(){ transFormCommand.execute(); } } public static void main(String[] args) { RealOperation realOperation = new RealOperation(); //构造四种命令 LeftCommand leftCommand = new LeftCommand(realOperation); RightCommand rightCommand = new RightCommand(realOperation); FallCommand fallCommand = new FallCommand(realOperation); TransFormCommand transFormCommand = new TransFormCommand(realOperation); Commander commander = new Commander(); commander.setLeftCommand(leftCommand); commander.setRightCommand(rightCommand); commander.setFallCommand(fallCommand); commander.setTransFormCommand(transFormCommand); commander.toLeft(); commander.toRight(); commander.fall(); commander.transForm(); //如果写realOperation.toLeft();是不是更容易接受？ //问题的是如果我需要一个命令是由已知的命令的组合怎么办？ //如果是命令模式，只需要新建一个Command然后自己实现就行，只需要拓展不需要修改（RealOperation） //如果不采用命令模式是需要修改RealOperation类的 }

3.总结

1.优点 命令模式的封装性很好，更弱的耦合性，更灵活的控制性以及更好的扩展性。 2.缺点 类的膨胀，大量衍生类的创建。