Exploration of PHP5.0 Object Model: Abstract Methods and Abstract Classes PHP Learning Network_PHP Tutorial

Object-oriented programs are built through a hierarchical structure of classes. In a single inheritance language such as PHP, the inheritance of classes is tree-like. A root class has one or more subclasses, and each class is divided into A subclass continues with one or more next-level subclasses. Of course, there may be multiple root classes used to implement different functions. In a well-designed system, each root class should have a useful interface that can be used by application code. If our application code is designed to work with the root class, it can also work with any subclass that continues from the root class.

Abstract method is a placeholder like a general method in a subclass (occupies a place but does not work), it is different from a general method