Introduction
In object oriented programming, an abstract class is the one that can be instantiated, i.e. it is not possible to declare object of such class. PHP supports concept of abstarct class since version 5.0
A class defined with abstract keyword becomes an abstract class. Further, any class which contains at least one abstract method is also considered abstract.
Syntax
如果我们尝试创建这个类的一个对象，PHP解析器会抛出以下错误：
$a=new testclass(); PHP Fatal error: Uncaught Error: Cannot instantiate abstract class testclass
abstract method
Abstract method only declares its signature i.e. its visibility, arguments and return type with type hints and donot have any functionality. A class that inherits such an abstract class must override (provide definition) all abstract methods. Corresponding method in child class must carry same signature as in parent class. If child class doesn't fulfil this condition, PHP parser throws exception. A class that extends an abstract class can now be instantiated, hence it is called concrete class
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In following example, parent class has two abstract methods, only one of which is redefined in child class. This results in error as follows −
Example
Live Demo
Output
Following is the error message
PHP Fatal error: Class myclass contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (testclass::hello)
Abstract method with arguments
When abstract method is defined with arguments, it must be overridden in child class with same number of arguments
In following example, abstract method in parent class has two arguments. Child class also defines same function with two arguments
Example
Live Demo
hello("Ravi",20);
?>输出
这将产生以下输出 −
My name is Ravi and my age is 20
