PHP objects, Patterns, and Practice

The book is about OOP and design patterns specifically for PHP5. It also includes chapters for CVS, PHPUnit, Phing, Pear and phpDocumentor. I pleased with reading and information in the book. The book is a good programmer reference.

Encapsulation

Encapsulation simply means the hiding of data and functionality from a client. On the simplest level, we encapsulate data by declaring properties private or protected. By hiding a property from client ode, we enforce an interface and prevent the accidental corruption of an object's data.

Polymorphism

Polymorphism, or class switching, is a common feature of object-oriented systems. Polymorphism is the maintenance implementations behind a common interface. Polymorphism illustrates another kind of encapsulation. By placing different implementations behind a common interface, we hide these underlying strategies from the client. This means that any changes that are made behind this interface are transparent to the wider system.