Behavioral patterns

Behavioral patterns are useful when we need to change an algorithm followed by objects dynamically, or to implement a special type of communication between instances. Using this type of template, we can observe state changes or send special commands to a certain object.

This section covers the following patterns:

• Observer
• Strategy
• Command
• State
• Chain of responsibility
• Visitor

Observer

The Observer pattern allows an object to determine the state change of another object. An instance that is interested can subscribe and immediately be notified when the value of a certain field is changed. The following diagram shows this case:

The preceding diagram contains the TextChangeListener interface, which is...