命令模式

简介

命令模式（Command Pattern）是一种数据驱动的设计模式，它属于行为型模式。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。

实现

1. 创建一个命令接口

public interface Order {
    void execute();
}

2. 创建一个请求类

public class Stock {
    private String name = "ABC";
    private int quantity = 10;

    public void buy(){
        System.out.println("购买 [名称: " + name + ", 数量: " + quantity + "]");
    }

    public void sell(){
        System.out.println("卖出 [名称: " + name + ", 数量: " + quantity + "]");
    }
}

3. 创建实现了Order接口的实体类

public class BuyStock implements Order {
    private Stock absStock;

    public BuyStock(Stock absStock) {
        this.absStock = absStock;
    }

    @Override
    public void execute() {
        absStock.buy();
    }
}

public class SellStock implements Order {
    private Stock absStock;

    public SellStock(Stock absStock) {
        this.absStock = absStock;
    }

    @Override
    public void execute() {
        absStock.sell();
    }
}

4. 创建命令调用类

public class Broker {
    private List<Order> orderList = new ArrayList<>();

    public void takeOrder(Order order){
        orderList.add(order);
    }

    public void placeOrders(){
        for (Order order : orderList) {
            order.execute();
        }
        orderList.clear();
    }
}

5. 使用broker类来接受并执行命令

public class CommandPatternDemo {
    public static void main(String[] args) {
        Stock stock = new Stock();

        BuyStock buyStockOrder = new BuyStock(stock);
        SellStock sellStockOrder = new SellStock(stock);

        Broker broker = new Broker();
        broker.takeOrder(buyStockOrder);
        broker.takeOrder(sellStockOrder);

        broker.placeOrders();
    }
}

类图

代码

命令模式 (opens new window)