TOUNA’s Blog – In memory of Turner

The Chain of Responsibility forwards requests along a chain of
classes, but the Command pattern forwards a request only to a specific
module. It encloses a request for a specific action inside an object and gives it
a known public interface. It lets you give the client the ability to make
requests without knowing anything about the actual action that will be
performed, and allows you to change that action without affecting the client
program in any way.
Motivation
When you build a Java user interface, you provide menu items,
buttons, and checkboxes and so forth to allow the user to tell the program
what to do. When a user selects one of these controls, the program receives an
ActionEvent, which it must trap by subclassing, the actionPerformed event.
Let’s suppose we build a very simple program that allows you to select the
menu items File | Open and File | Exit, and click on a button marked Red
which turns the background of the window red. This program is shown
below.

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