标题：Java命令模式

命令模式是数据驱动设计模式，属于行为模式类别。 请求作为命令包装在一个对象下，并传递给调用器对象。 调用者对象查找可以处理此命令的适当对象，并将命令传递到执行命令的相应对象。

实现实例

在这个示例中，创建了一个作为命令的接口- Order，同时也创建了一个Stock类作为请求。 有具体的命令类BuyStock和SellStock实现Order接口将做实际的命令处理。 将创建一个类Broker作为调用器对象。它可以接收和下订单。

Broker对象使用命令模式来标识哪个对象，并根据命令类型执行哪个命令。 CommandPatternDemo这是一个演示入口类，将使用Broker类演示命令模式。

命令模式的实现实例结构如下图中所示 -

第1步

创建一个命令接口。实现代码如下所示 -

Order.java

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public interface Order {
   void execute();
}
Java

public interface Order {
   void execute();
}
Java

第2步

创建一个请求对象
Stock.java

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public class Stock {
 
   private String name = "ABC";
   private int quantity = 10;
 
   public void buy(){
      System.out.println("Stock [ Name: "+name+", 
         Quantity: " + quantity +" ] bought");
   }
   public void sell(){
      System.out.println("Stock [ Name: "+name+", 
         Quantity: " + quantity +" ] sold");
   }
}
Java

public class Stock {

   private String name = "ABC";
   private int quantity = 10;

   public void buy(){
      System.out.println("Stock [ Name: "+name+", 
         Quantity: " + quantity +" ] bought");
   }
   public void sell(){
      System.out.println("Stock [ Name: "+name+", 
         Quantity: " + quantity +" ] sold");
   }
}
Java

第3步

创建实现Order接口的具体类。

BuyStock.java

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public class BuyStock implements Order {
   private Stock abcStock;
 
   public BuyStock(Stock abcStock){
      this.abcStock = abcStock;
   }
 
   public void execute() {
      abcStock.buy();
   }
}
Java

public class BuyStock implements Order {
   private Stock abcStock;

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

   public void execute() {
      abcStock.buy();
   }
}
Java

SellStock.java

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public class SellStock implements Order {
   private Stock abcStock;
 
   public SellStock(Stock abcStock){
      this.abcStock = abcStock;
   }
 
   public void execute() {
      abcStock.sell();
   }
}
Java

public class SellStock implements Order {
   private Stock abcStock;

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

   public void execute() {
      abcStock.sell();
   }
}
Java

第4步

创建命令调用程序类。
Broker.java

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

import java.util.ArrayList;
import java.util.List;

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

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

   public void placeOrders(){

      for (Order order : orderList) {
         order.execute();
      }
      orderList.clear();
   }
}
Java

第5步

使用Broker类来接收和执行命令。
CommandPatternDemo.java

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public class CommandPatternDemo {
   public static void main(String[] args) {
      Stock abcStock = new Stock();
 
      BuyStock buyStockOrder = new BuyStock(abcStock);
      SellStock sellStockOrder = new SellStock(abcStock);
 
      Broker broker = new Broker();
      broker.takeOrder(buyStockOrder);
      broker.takeOrder(sellStockOrder);
 
      broker.placeOrders();
   }
}
Java

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

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

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

      broker.placeOrders();
   }
}
Java

第6步

验证输出，执行上面的代码得到以下结果 -

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Stock [ Name: ABC, Quantity: 10 ] bought
Stock [ Name: ABC, Quantity: 10 ] sold
Java

Stock [ Name: ABC, Quantity: 10 ] bought
Stock [ Name: ABC, Quantity: 10 ] sold
Java