PHP abstract classes, interfaces, final, class constants advanced learning tutorial

Advanced learning of PHP object-oriented, mainly including some information on abstract classes, interfaces, final, and class constants

1. Abstract classes (abstract)
In our actual development process, some classes do not need to be instantiated. For example, some parent classes learned earlier are mainly inherited by subclasses, which can improve code reusability.
Grammar structure :

abstract class 类名{ 
属性 $name; 
方法(){} //方法也可以为abstract 修饰符 function 方法名(){} 
}

Example:

abstract class animal{ 
public $name; 
public $age; 
//抽象方法不能有方法体，主要是为了让子类去实现; 
abstract public function cry(); 
//
抽象类
中可以包含抽象方法，同时也可以包含实例类方法 
public function getname(){ 
echo $this->name; 
} 
} 
class Cat{ 
public function cry(){ 
echo 'ok'; 
} 
}

Understanding: Animal class is actually an abstract concept, which stipulates some common attributes and behaviors of some animals, but in fact it does not itself have those attributes and behaviors. Another example: transportation classes, plant classes, etc.

Note:
1. If a class is modified with abstract, then the class is an abstract class. If a method is modified with abstract, then the class A method is an abstract method. An abstract method cannot have a method body => abstract function cry(); not even {}.
2. An abstract class must not be instantiated. An abstract class can have no abstract method, but if A class contains any abstract method, and this class must be declared as an abstract class;
3. If a class inherits another abstract class, the subclass must implement all abstract methods in the abstract class (unless it itself Also declared as an abstract class);

2. Interface (interface)
The interface is to encapsulate some unimplemented methods together. When a certain class is used, Then write these methods according to the specific situation;
Grammar structure
interface interface name {
//Attributes, methods
//Methods in the interface cannot have method bodies;
}
How to implement the interface
class class name implements interface name{

}
Understanding: The interface is a more abstract abstract class. The methods in the abstract class can have method bodies, but the methods in the interface There must be no method body. The interface realizes the polymorphism of programming and the design ideas of high cohesion and low coupling;

Example:

//接口是定义规范、属性的，一般以小写的i开头； 
interface iUsb{ 
public function start(); 
public function stop(); 
} 
//编写相机类，让它去实现接口 
//当一个类实现了某个接口，那么该类就必须实现接口的所有方法 
class Camera implements iUsb{ 
public function start(){ 
echo 'Camera Start Work'; 
} 
public function stop(){ 
echo 'Camera Stop Work'; 
} 
} 
//编写一个手机类 
class Phone implements iUsb{ 
public function start(){ 
echo 'Phone Satrt Work'; 
} 
public function stop(){ 
echo 'Phone Stop Work'; 
} 
} 
$c=new Camera(); 
$c->start(); 
$p=new Phone(); 
$p->start();

When to use interfaces:
1. Set specifications and let others Programmers to implement
2. When multiple parallel classes need to implement a certain function, but the implementation methods are different;

Summary:
1. The interface cannot be instantiated , all methods in the interface cannot have a body;
2. A class can implement multiple interfaces, separated by commas (,) class demo implements if1,if2,if3{}
3. The interface can have attributes , but it must be a constant. A constant cannot have modifiers (the default is public modifier) ​​
For example: interface iUsb{
const A=90;
}
echo iUsb::A;
4. All methods in the interface must be public, and the default is public;
5. An interface cannot inherit from other classes, but it can inherit from other interfaces. An interface can inherit from multiple other classes. Interface
For example: interface interface nameextends if1,if2{}
6. A class can inherit other interfaces while inheriting the parent class
For example: class test extends testbase implements test1, test2{}

Implementing the interface VS inheriting the class
The inheritance of PHP is single inheritance, that is, a class can only inherit one parent class, which has a certain impact on the expansion of the functions of the subclass. Implementing interfaces can be seen as a supplement to inherited classes. Inheritance is a hierarchical relationship and is not very flexible, while implementing interfaces is a horizontal relationship. Implementing interfaces can extend a certain function without breaking the inheritance relationship, which is very flexible.

3. Final

1. If we want a certain class not to be inherited by other classes (for example, for security reasons, etc.), then we can consider using final
Grammar:
final class A{}
2. If we want a method not to be overridden by subclasses, we can consider using final to modify it. The method modified by final can still be inherited, because the method Inheritance rights depend on public modification
such as:

class A{ 
final public function getrate($salary){ 
return $salary*0.08; 
} 
} 
class B extens A{ 
//这里父类的getrate方法使用了final，所以这里无法再重写getrate 
//public function getrate($salary){ 
// return $salary*0.01; 
//} 
}

3. Final cannot be used to modify attributes

4. Class constants (const)

In some cases, there may be such a requirement: when you do not want a member variable to be modified and want the value of the variable to be fixed, you can use const constants (const names should be in all uppercase letters and without $ symbol, constants cannot be modified)
Syntax:
const constant name = constant value; //An initial value must be assigned, because the constant cannot be modified
Call:
Class name:: Constant name [self::constant name available inside this class] or interface name::constant name //Only constants can be used in the interface, variables cannot be used
For example:

class A{ 
const TAX_RATE=0.08; 
function paytax($salary){ 
return $salary*self::TAX_RATE; 
} 
} 
$a=new A(); 
echo $a->paytax(100);

Note:
1 , Constants can be inherited by subclasses
2. Constants belong to a certain class, not to an object

The above is the detailed content of PHP abstract classes, interfaces, final, class constants advanced learning tutorial. For more information, please follow other related articles on the PHP Chinese website!