Problem

Take remote for example, user press buttons to perform action on TV. We can do it with code like:

  public class Remote {
      //....
      private TV tv;
      //...
      public turnOn() {
          //turn on tv logic e.g. tv.turnOn()
      }
  }

For above example, there are some problems :

1. Violate open-closed principle. If there are new action or existing action changed, developer need to change existing code

2. It is code to implementation rather than interface

3. Remote(invoker) and TV(receiver) are tightly couple

Command Pattern

In order to sovle these problems, command pattern comes. It looks like:

Example

There are some real world examples which use command pattern:

• Runnable interface (java.lang.Runnable)

• Invocation of Struts Action class by Action Servlet