PHP object-oriented inheritance

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Inheritance

Definition

The subclass inherits all the parent class’s-public and protected properties and methods.

Use the keyword extendsInheritance. One class integrates another and cannot inherit more than one.

Related professional terms

子类、父类、基类、超类、派生类

Subclass, derived class——> Class inherited from the base class;

Parent class, base class, super class refers to——> ; Inherited class.

Example

<?php

class Father
{
    public $a = &#39;public&#39;;
    protected $b = &#39;protected&#39;;
    private $c = &#39;private&#39;;

    public function func1()
    {
        echo &#39;This is public function&#39;,&#39;<br/>&#39;;
    }

    protected function func2()
    {
        echo &#39;This is protected function&#39;,&#39;<br/>&#39;;
    }

    private function func3()
    {
        echo &#39;This is private function&#39;,&#39;<br/>&#39;;
    }
}

// 继承父类
class Child extends Father
{
    // 子类中调用继承来的方法
    public function test()
    {
        $this -> func1();
        $this -> func2();
        //$this -> func3();  私有方法不可以调用
    }
}

// 实例化子类
$son = new Child();


// 尝试调用属性
echo $son -> a,&#39;<br/>&#39;;
//echo $son->b;   不能直接输出b
//echo $son -> c; 继承都没继承，当然不能输出


// 尝试调用方法
//$son -> func1();
//$son -> func2();   不能在类外调用func2
//$son -> func3();   继承都没继承，当然不能调用

// 间接调用继承自父类的普通方法
$son -> test();

Rewrite

Definition:

1) Inherit the method of the parent class, and the definition in the subclass is the same as that of the parent class Method with the same name in class , and has the same number of parameters ;

2) When the subclass overrides the method in the parent class, PHP will not call the method in the parent class Overridden method;

3) Whether to call the method of the parent class depends on the subclass.

4) When implementing method coverage, the access modifier can be different , but the access scope of the subclass must be greater than or equal to the parent class Access scope .

Usage:

parent::    访问父类中被重写的属性和方法

Example

<?php

class Father
{
    public function shuo($num)
    {
        echo &#39;a a o o&#39;;
    }
}


class Son extends Father
{
    public function shuo($num)
    {
        // 调用父类中被重写的方法
        // parent::shuo($num);

        echo &#39;Hello World&#39;;
    }

    public function test($num)
    {
        parent::shuo($num);
    }
}

// 实例化子类
$son1 = new Son();
$son1 -> shuo(1);   // Hello World
$son1 -> test(1);   // a a o o

final keyword

If the method in the parent class is declared final, then Subclasses cannot override this method.

If a class is declared final, it cannot be inherited.

Example

<?php

class Father
{
    final public function test()
    {
        echo &#39;hello&#39;;
    }
}

class Son extends Father
{
    public function test()
    {
        echo &#39;你好&#39;;
    }
}

// 实例化子类
$son1 = new Son();

$son1 -> test();  // 报错，函数不能被重写

Related recommendations:

php object-oriented overloading

php object-oriented Encapsulation

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