Object Abstraction

PHP 5 introduces abstract classes and methods. An abstract method only declares the method's signature and does not provide an implementation. A class that contains abstract methods needs to be declared abstract.

例子 14-4.

class AbstractClass {
abstract public function test();

ImplementedClass extends AbstractClass {
public function test() {
"ImplementedClass::test() called.\n";

$o = new ImplementedClass;

Abstract classes cannot be instantiated. Old code that has no user-defined classes or functions named 'abstract' should run without modifications.