JAVA设计模式之【命令模式】

命令模式
	为了降低耦合度，将请求的发送者和接收者解耦
	发送请求的对象只需要哦知道如何发送请求，而不必知道如何完成请求
	对请求排队
	记录请求日志
	支持撤销操作
	核心在于引入命令类
	角色
		抽象命令类Command
		具体命令类ConcreteCommand
		调用者Invoker
		接收者Receiver
	请求的一方不必知道接收请求的一方，更不必知道请求如何被接收、执行、怎么执行、何时执行

看例子，电视遥控器，电视，人。

1.抽象命令类,或接口

package Command;

/**
 * Created by Jiqing on 2016/10/26.
 */
public interface AbstractCommand {
    public void execute();
}

2.命令接收者电视机

package Command;

/**
 * Created by Jiqing on 2016/10/26.
 */
public class Television {
    public void open() {
        System.out.println("打开电视机");
    }

    public void close() {
        System.out.println("关闭电视机");
    }

    public void changeChannel() {
        System.out.println("切换电视频道");
    }
}

3.具体命令
a.打开命令

package Command;

/**
 * Created by Jiqing on 2016/10/26.
 */
public class TVOpenCommand implements AbstractCommand{
    private Television tv;
    public TVOpenCommand() {
        tv = new Television();
    }

    public void execute() {
        tv.open();
    }
}

b.关闭命令

package Command;

/**
 * Created by Jiqing on 2016/10/26.
 */
public class TVCloseCommand implements AbstractCommand{
    private Television tv;
    public TVCloseCommand() {
        tv = new Television();
    }

    public void execute() {
        tv.close();
    }
}

c.更改频道命令

package Command;

/**
 * Created by Jiqing on 2016/10/26.
 */
public class TVChangeCommand implements AbstractCommand{
    private Television tv;
    public TVChangeCommand() {
        tv = new Television();
    }

    public void execute() {
        tv.changeChannel();
    }
}

4.命令发布者控制者,人

package Command;

/**
 * Created by Jiqing on 2016/10/26.
 */
public class Controller {
    private AbstractCommand openCommand,closeCommand,changeCommand;
    public Controller(AbstractCommand openCommand,AbstractCommand closeCommand,AbstractCommand changeCommand) {
        this.openCommand = openCommand;
        this.closeCommand = closeCommand;
        this.changeCommand = changeCommand;
    }

    public void open() {
        openCommand.execute();
    }

    public void change() {
        changeCommand.execute();
    }

    public void close() {
        closeCommand.execute();
    }
}

5.客户端

package Command;

/**
 * Created by Jiqing on 2016/10/26.
 */
public class Client {
    public static void main(String a[]) {
        AbstractCommand openCommand,closeCommand,changeCommand;

        openCommand = new TVOpenCommand();
        closeCommand = new TVCloseCommand();
        changeCommand = new TVChangeCommand();

        Controller control = new Controller(openCommand,closeCommand,changeCommand);

        control.open();
        control.close();
        control.change();
    }
}

执行结果：

打开电视机
关闭电视机
切换电视频道

再看一个撤销案例

package Command.Undo;
abstract class AbstractCommand
{
    public abstract int execute(int value);
    public abstract int undo();
}

class ConcreteCommand extends AbstractCommand
{
    private Adder adder = new Adder();
    private int value;

    public int execute(int value)
    {
        this.value=value;
        return adder.add(value);
    }

    public int undo()
    {
        return adder.add(-value);
    }
}

class CalculatorForm
{
    private AbstractCommand command;

    public void setCommand(AbstractCommand command)
    {
        this.command=command;
    }

    public void compute(int value)
    {
        int i = command.execute(value);
        System.out.println("执行运算，运算结果为：" + i);
    }

    public void undo()
    {
        int i = command.undo();
        System.out.println("执行撤销，运算结果为：" + i);
    }
}

class Adder
{
    private int num=0;

    public int add(int value)
    {
        num+=value;
        return num;
    }
}

class Client
{
    public static void main(String args[])
    {
        CalculatorForm form = new CalculatorForm();
        ConcreteCommand command = new ConcreteCommand();
        form.setCommand(command);

        form.compute(10);
        form.compute(5);
        form.compute(10);
        form.undo();
    }
}

执行结果：

执行运算，运算结果为：10
执行运算，运算结果为：15
执行运算，运算结果为：25
执行撤销，运算结果为：15

看类图