PHP abstract class inherits abstract class uml abstract class abstract class example

For PHP programmers, the most difficult point to master is the knowledge point of PHP abstract class application. As a novice, I am not yet ready to use object-oriented knowledge to program, but in future development, it is inevitable to use classes to encapsulate or use interfaces to develop programs in various modular formats.

In natural language, we understand abstract concepts as a large description of an object, which is a common characteristic for a certain type of object. The same is true in PHP. When we abstract a class, we can indicate the general behavior of the class. This class should be a template, which indicates some behaviors that its sub-methods must implement.

Definition of PHP abstract class application:

abstract class ClassName{

}

Key points of PHP abstract class application:

　1. Define some methods, and subclasses must fully implement all methods in this abstraction

　2. Can’t Create an object from an abstract class, its meaning is to be extended

　3.Abstract classes usually have abstract methods, there are no braces in the methods

PHP abstract class application points:

　1. Abstract methods do not have to implement specific functions. Completed by subclasses

　2. When a subclass implements a method of an abstract class, the visibility of the subclass must be greater than or equal to the definition of the abstract method

　3. The method of an abstract class can have parameters or be empty

　4. If the abstract method has parameters, then the implementation of the subclass must also have the same number of parameters

PHP abstract class application example:

abstract public function_name(); //Note that there are no curly brackets

PHP abstract class rules ：

1. As long as a class contains at least one abstract method, it must be declared as an abstract class
2. Abstract methods cannot contain function bodies
3. Inherit subclasses of abstract classes, and those that implement abstract methods must be related to the abstract method The same or lower access level
4. Inherits a subclass of an abstract class. If all abstract methods are not implemented, then the subclass is also an abstract class

As a demonstration, let’s implement a simple abstract class: Calculate the area of ​​a rectangle . This rectangle can be extended from the shape class.

PHP   
<span>abstract</span><span>class</span><span> Shape {   
</span><span>abstract</span><span>protected</span><span>function</span><span> get_area();   
</span><span>//</span><span>和一般的方法不同的是，这个方法没有大括号   
//你不能创建这个抽象类的实例：$Shape_Rect</span>= <span>new</span><span> Shape(); 
}   
</span><span>class</span> Rectangle <span>extends</span><span> Shape{   
</span><span>private</span><span>$width</span><span>;   
</span><span>private</span><span>$height</span><span>;   
</span><span>function</span> __construct(<span>$width</span>=0,
<span>$height</span>=0<span>){   

　　</span><span>$this</span>->width=<span>$width</span><span>;   
</span><span>　　$this</span>->height=<span>$height</span><span>;   
}   
</span><span>function</span><span> get_area(){   
</span><span>　　echo</span> (<span>$this</span>->width+<span>$this</span>->height)*2<span>;   
}   
}   
</span><span>$Shape_Rect</span> = <span>new</span> Rectangle(20,30<span>);   
</span><span>$Shape_Rect</span>-><span>get_area();   
</span>?>   

This is also a simple example, which basically illustrates the usage of abstract classes in PHP. I don’t want to say more about the rest. Personally, I think abstract classes are generally used in large projects, because I think it has too many "rules" to abide by, making it inconvenient to use! Of course this is just my opinion. I would like to say more. PHP abstract class applications are single inheritance, which means that you can only inherit from one class, but not one class that inherits class A and class B. If you want to implement such a function, you have to use an interface. Related knowledge, I will not discuss the knowledge of PHP interface for the time being! In a word: Single inheritance and multiple interfaces!

The above has introduced PHP abstract classes, including PHP and abstract class content. I hope it will be helpful to friends who are interested in PHP tutorials.