
Creational Design Patterns
- Design Patterns - Factory Pattern
- Abstract Factory Pattern
- Design Patterns - Singleton Pattern
- Design Patterns - Builder Pattern
- Design Patterns - Prototype Pattern
Structural Design Patterns
- Design Patterns - Adapter Pattern
- Design Patterns - Bridge Pattern
- Design Patterns - Filter Pattern
- Design Patterns - Composite Pattern
- Design Patterns - Decorator Pattern
- Design Patterns - Facade Pattern
- Design Patterns - Flyweight Pattern
- Design Patterns - Proxy Pattern
- Chain of Responsibility Pattern
Behavioral Design Patterns
- Design Patterns - Command Pattern
- Design Patterns - Interpreter Pattern
- Design Patterns - Iterator Pattern
- Design Patterns - Mediator Pattern
- Design Patterns - Memento Pattern
- Design Patterns - Observer Pattern
- Design Patterns - State Pattern
- Design Patterns - Strategy Pattern
- Design Patterns - Template Pattern
- Design Patterns - Visitor Pattern
J2EE Design Patterns
- Design Patterns - Null Object Pattern
- Design Patterns - MVC Pattern
- Business Delegate Pattern
- Composite Entity Pattern
- Data Access Object Pattern
- Front Controller Pattern
- Intercepting Filter Pattern
- Service Locator Pattern
- Transfer Object Pattern
Design Patterns Useful Resources
Design Patterns - Command Pattern
Overview
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
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 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 1
Create a command interface.
Order.java
package com.tutorialspoint; public interface Order { void execute(); }
Step 2
Create a request class.
Stock.java
package com.tutorialspoint; 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
Create concrete classes implementing the Order interface.
BuyStock.java
package com.tutorialspoint; public class BuyStock implements Order { private Stock abcStock; public BuyStock(Stock abcStock){ this.abcStock = abcStock; } public void execute() { abcStock.buy(); } }
SellStock.java
package com.tutorialspoint; public class SellStock implements Order { private Stock abcStock; public SellStock(Stock abcStock){ this.abcStock = abcStock; } public void execute() { abcStock.sell(); } }
Step 4
Create command invoker class.
Broker.java
package com.tutorialspoint; 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(); } }
Example - Usage of Command Pattern
Use the Broker class to take and execute commands.
CommandPatternDemo.java
package com.tutorialspoint; import java.util.ArrayList; import java.util.List; 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(); } } interface Order { void execute(); } 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"); } } class BuyStock implements Order { private Stock abcStock; public BuyStock(Stock abcStock){ this.abcStock = abcStock; } public void execute() { abcStock.buy(); } } class SellStock implements Order { private Stock abcStock; public SellStock(Stock abcStock){ this.abcStock = abcStock; } public void execute() { abcStock.sell(); } } 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(); } }
Output
Verify the output.
Stock [ Name: ABC, Quantity: 10 ] bought Stock [ Name: ABC, Quantity: 10 ] sold