Design Pattern 简明教程
Design Patterns - Command Pattern
命令模式是一种数据驱动设计模式，属于行为模式类别。一个请求被包装在对象中作为命令并传递给调用对象。调用对象寻找可以处理此命令的适当对象，并将该命令传递给执行该命令的对应对象。
Command pattern is a data driven design pattern and falls under behavioral pattern category. A request is wrapped under an object as command and passed to invoker object. Invoker object looks for the appropriate object which can handle this command and passes the command to the corresponding object which executes the command.
Implementation
我们创建了一个作为命令的接口 Order。我们创建了一个充当请求的 Stock 类。我们创建了实现 Order 接口的具体命令类 BuyStock 和 SellStock，这些类将执行实际的命令处理。创建了一个作为调用对象充当角色的 Broker 类。它可以接收并下达订单。
We have created an interface Order which is acting as a command. We have created a Stock class which acts as a request. We have concrete command classes BuyStock and SellStock implementing Order interface which will do actual command processing. A class Broker is created which acts as an invoker object. It can take and place orders.
Broker 对象使用命令模式来根据命令类型识别哪个对象将执行哪个命令。我们的演示类 CommandPatternDemo 将使用 Broker 类来演示命令模式。
Broker object uses command pattern to identify which object will execute which command based on the type of command. CommandPatternDemo, our demo class, will use Broker class to demonstrate command pattern.
Step 2
创建一个请求类。
Create a request class.
Stock.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");
}
}Step 3
创建实现 Order 接口的具体类。
Create concrete classes implementing the Order interface.
BuyStock.java
public class BuyStock implements Order {
private Stock abcStock;
public BuyStock(Stock abcStock){
this.abcStock = abcStock;
}
public void execute() {
abcStock.buy();
}
}SellStock.java
public class SellStock implements Order {
private Stock abcStock;
public SellStock(Stock abcStock){
this.abcStock = abcStock;
}
public void execute() {
abcStock.sell();
}
}Step 4
创建命令调用者类。
Create command invoker class.
Broker.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();
}
}Step 5
使用 Broker 类获取并执行命令。
Use the Broker class to take and execute commands.
CommandPatternDemo.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();
}
}