命令模式把一个请求或者操作封装到一个对象中，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。
命令模式结构：
客户角色：创建一个具体命令对象并确定其接收者
命令角色：声明了一个给所有具体命令类的抽象接口
具体命令角色：定义一个接收者和行为之间的弱耦合，实现execute()方法，负责调用接收者的相应操作
请求者角色：负责调用命令对象执行请求
接收者角色：负责具体实施和执行一个请求
1public class Client{
2 public static void main(String[] args){
3 Receiver receiver = new Receiver();
4 Command commandOne = new ConcreteCommandOne(receiver);
5 Command commandTwo = new ConcreteCommandTwo(receiver);
6 Invoker invoker = new Invoker(commandOne,commandTwo);
7 invoker.actionOne();
8 invoker.actionTwo();
9 }
10}
11public class Invoker{
12 private Command commandOne;
13 private Command commandTwo;
14 public Invoker(Command commandOne,Command commandTwo){
15 this.commandOne = commandOne;
16 this.commandTwo = commandTwo;
17 }
18 public void actionOne(){
19 commandOne.execute();
20 }
21 public void actionTwo(){
22 commandTwo.execute();
23 }
24}
25public interface Command{
26 void execute();
27}
28public class ConcreteCommandOne implements Command{
29 private Receiver receiver
30 public ConcreteCommandOne(Receiver receiver){
31 this.receiver = receiver;
32 }
33 public void execute(){
34 receiver.actionOne();
35 }
36}
37public class ConcreteCommandTwo implements Command{
38 private Receiver receiver
39 public ConcreteCommandTwo(Receiver receiver){
40 this.receiver = receiver;
41 }
42 public void execute(){
43 receiver.actionTwo();
44 }
45}
46public class Receiver{
47 public Receiver(){
48 //
49 }
50 public void actionOne(){
51 System.out.println("ActionOne has been taken.");
52 }
53 public void actionTwo(){
54 System.out.println("ActionTwo has been taken.");
55 }
56}