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。