Understand PHP classes, objects, abstract classes, and interfaces in one article

Classes and objects: abstract classes, interfaces

Abstract classes and interfaces: Abstract classes (Abstract Class) and interfaces (Interface) are special that cannot be instantiated kind.

Abstract class:

The abstract methods in abstract classes are empty methods without specific implementation. Abstract classes can be used to set functional definitions for subclasses, so abstract classes force developers to inherit only from a specific parent class

#, and then complete what they need in the inherited subclass specific functions.

The syntax format for defining an abstract class is as follows:

abstract class 类名称{
　　//抽象类的成员变量列表
　　abstract function 成员方法1([参数1]，[参数2]，……);
　　abstract function 成员方法2([参数1]，[参数2]，……);
　　//其他代码
}

Abstract classes are similar to ordinary classes and also have member attributes and member methods. , the difference is that abstract classes cannot be instantiated.

The following defines a simple and complete abstract class:

abstract class MyClass{ //定义抽象类
　　abstract protected function myFunction($arg); //定义抽象方法
}

PS: The definition of the abstract class must contain at least one modified with the keyword abstract and without any implementation abstract method.

Implementation process of abstract class:

In an abstract class, not only can abstract methods be defined, but also some member methods that can complete specified functions can be defined like ordinary classes. When subclasses inherit After abstracting the class, you can

directly reference these member methods that can complete the specified functions.

class 子类名称 extends 抽象类名称{
　　//子类的成员变量列表
　　
　　function 抽象方法名称([参数1]，[参数2]，……){
　　    //抽象方法的具体实现
　　}
　　//其他代码
　}

PS: When a class inherits from an abstract class, it must contain all methods defined in the abstract class, otherwise an error will occur during runtime.

The following is an example of implementing an abstract class:

abstract class Study{
　　abstract function printStudy($name,$lang); //定义一个抽象方法
}
 
class OneStudy extends Study { //定义子类继承于父类
　　function printStudy($name,$lang){ //抽象方法的具体实现
　　    echo $name."正在整理".$lang."……";
　　}
　}
　
class TwoStudy extends Study {
　　function printStudy($name,$lang){
　　    echo $name."正在整理".$lang."……";
    }
}
　　$first=new OneStudy();
　　$first->printStudy("大兵","PHP基础知识");
　　echo "";
　　$second=new TwoStudy();
　　$second->printStudy("小兵","SEO基础知识");

The running result of this program is:

The soldiers are sorting out the basic knowledge of PHP... …

Xiaobing is sorting out the basic knowledge of SEO…

Define the interface:

The interface is a collection of member method declarations, which only contains some Empty member methods or some class constants. These empty member methods will be implemented by the class that implements the interface.

You need to use the keyword interface to define an interface. The syntax format is as follows:

interface 接口名称{
　　//类常量列表
　　function 成员方法1([参数1]，[参数2]，……);
　　function 成员方法2([参数1]，[参数2]，……);
　　//其他代码
}

Since the interface cannot be instantiated, there is no construction method or destructuring method in the interface. It only needs to give a set of The declaration of the member method to be implemented is enough.

The following defines a simple and complete interface:

interface class MyClass{ //定义接口
　　public function myFunction($arg); //定义方法
}

The implementation process of the interface:

Similar to the class, the interface Can also be inherited. An interface can inherit from multiple interfaces, but an interface cannot inherit from a class. To implement an interface, use the keyword implements.

When using a class to implement an interface, it must contain at least all the methods defined in the interface, otherwise an error will occur at runtime.

The following is an example of implementing an interface:

interface IName{ //定义接口IName
　　function setName($name);
　　function getName();
　　}
　　interface IAge{ //定义接口IAge
　　function setAge($age);
　　function getAge();
　　}
　　class DaBing implements IName,IAge{ //定义实现接口的类
　　private $name;
　　private $age;
　　function setName($name){
　　$this->name=$name;
　　}
　　function getName(){
　　echo "姓名：".$this->name." ";
　　}
　　function setAge($age){
　　$this->age=$age;
　　}
　　function getAge(){
　　echo "年龄：".$this->age;
　　}
　　}
　　$obj=new DaBing();
　　$obj->setName("大兵");
　　$obj->getName();
　　$obj->setAge(25);
　　$obj->getAge();

The running result of this program is:

Name: Soldier Age: 25

Abstract classes and interfaces Difference:

The use of interfaces is achieved through the keyword implements. Operations on abstract classes are implemented by inheriting the keyword extends.

Interfaces have no data members, but abstract classes have data members, and abstract classes can achieve data closure.

Interfaces do not have constructors, and abstract classes can have constructors.

Methods in interfaces are of public type, while methods in abstract classes can be modified with private, protected or public.

A class can implement multiple interfaces at the same time, but a class can only inherit from one abstract class.

There cannot be implementation code for member methods in an interface, but there can be implementation code for member methods in an abstract class.

PS: In the application, if you need to add more behaviors to a certain class, you can define an interface to combine these behaviors. If you need to reuse the data and behavior of a certain thing, you should define an abstract class to encapsulate these variables and functions.

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