1、概念

    请求以命令的形式包裹在对象中，并传给调用对象。调用对象寻找可以处理该命令的合适的对象，并把该命令传给相应的对象，该对象执行命令。

2、场景

    2.1 ：工作流Activit框架中就用到了这种模式，它总共7个接口，每个接口都有特定的命令去执行数据库中的表，因为activit框架会自动生成23张表，所以这些命令都会在这些表中直接增删改查，我们在后台直接调用这些命令就好。

3、简单代码实现

public interface Order {    void execute();}

public class Apple {    private String name = "ABC";    private int quantity = 10;    public void buy(){        System.out.println("买家name="+name+" quantity="+quantity);    }    public void sell(){        System.out.println("卖家name="+name+" quantity="+quantity);    }}

public class BuyApple implements Order {    private Apple apple;    public BuyApple(Apple apple) {        this.apple = apple;    }    @Override    public void execute() {        apple.buy();    }}

public class SellApple implements Order {    private Apple apple;    public SellApple(Apple apple){        this.apple = apple;    }    @Override    public void execute() {        apple.sell();    }}

public class Command {    private List
    
      orderList = new ArrayList<>();    public void takeOrder(Order order){        orderList.add(order);    }    public void placeOrders(){        for (Order order : orderList) {            order.execute();        }        orderList.clear();    }}
    

main函数执行结果

public class Main {    public static void main(String[] args) {        Apple apple = new Apple();        BuyApple buyStockOrder = new BuyApple(apple);        SellApple sellStockOrder = new SellApple(apple);        Command command = new Command();        command.takeOrder(buyStockOrder);        command.takeOrder(sellStockOrder);        command.placeOrders();    }}