OOP的第二大特性--继承性

Posted 2020-07-10

　　1,类继承的应用

　　子类继承父类，拥有父类的属性和方法.

　　代码:

 1 <?php
 2 header("Content-Type:text/html;charset=utf-8");
 3 
 4 //声明一个人类
 5 
 6 class Person
 7 {
 8     //属性
 9     public $sex;
10     public $name;
11     public $age;
12     public $height;
13     //方法
14     public function eat()
15     {
16         echo "我会吃！<br>";
17     }
18 
19     public function sleep()
20     {
21         echo "我能睡！<br>";
22     }
23 }
24 
25 //男人类
26 class Man
27 {
28     //属性
29     public $name;
30     public $age;
31     public $sex = ‘男‘;
32     public $height;
33     public $hou;
34 
35     //方法
36     public function eat()
37     {
38         echo "我会吃！<br>";
39     }
40 
41     public function sleep()
42     {
43         echo "我能睡！<br>";
44     }
45 
46     public function peeStand()
47     {
48         echo "我会站着尿尿<br>";
49     }
50 }
51 
52 //定一个超级英雄类
53 class SuperMan
54 {
55     //属性
56     public $name;
57     public $age;
58     public $sex = ‘男‘;
59     public $height;
60     public $hou;
61     public $energy;
62 
63     //方法
64     public function eat()
65     {
66         echo "我会吃！<br>";
67     }
68 
69     public function sleep()
70     {
71         echo "我能睡！<br>";
72     }
73 
74     public function peeStand()
75     {
76         echo "我会站着尿尿<br>";
77     }
78 
79     public function fly()
80     {
81         echo "我会飞翔！<br>";
82     }
83 }

 

　　格式：
        class 子类名 extends 父类名
        {
            code...
        }
     特点：
            ① 一个父类（基类）可以被多个子类继承
            ② 一个子类不能同时继承多个父类

　　

　2、继承的访问控制

位置	public	protected	private
在类的外部	Y	N	N
在子类的内部	Y	Y	N
在类的内部	Y	Y	Y

　　

　　　　　代码:　

<?php
header("Content-Type:text/html;charset=utf-8");
//子类重写父类属性
class User
{
    public $name = "马克思";
    protected $age = 40;
    private $money = "一百亿元";
    
    protected function getInfo()
    {
        echo "这是父类的get<br>";
        echo "name:".$this->name."|age:".$this->age."|money:".$this->money."<br>";
    }
}
class VipUser extends User
{
    public $name = "乔布斯";
    //protected $name = "乔布斯";
    
    //public $age = 50;
    protected $age = 50;
    
    public $money = ‘一块钱‘;
    
    public function demo()
    {
        echo "在子类的内部访问父类的public属性:".$this->name."<br>";
        echo "在子类的内部访问父类的protected属性:".$this->age."<br>";
        echo "在子类的内部访问父类的private属性:".$this->money."<br>";
    }
    
    public function getInfo()
    {
        echo "这是子类的get<br>";
        echo "name:".$this->name."|age:".$this->age."|money:".$this->money."<br>";
    }
}
echo "<pre>";
//实例化
$user = new User();
$vip = new VipUser();
$vip->getInfo();
echo "<hr>";
var_dump($user);
var_dump($vip);

　　输出结果:

　　

 

　　3、子类中重写父类方法
        ① 子类中可以重写父类的属性和方法
        ② 子类重写非私有方法和属性时 只能更加开放 level更低
        ③ 重载父类方法 parent::父类方法名()

　　代码:

　　

<?php  
header("Content-Type:text/html;charset=utf-8");
//子类重写父类属性
class User
{
    public $name = "马克思";
    protected $age = 40;
    private $money = "十一亿";

    public function __construct($name,$age)
    {
        $this->name=$name;
        $this->age = $age;
    }
    public function getInfo()
    {
        echo "这是父类的get<get>";;
        echo "name".$this->name."|age:".$this->age."|money:".$this->money."<br>";
    }
    public function demo()
    {
        echo "父demo <br>";
    }
}
class VipUser extends User
{
    public $home;
    private $money;

    public function __construct($name,$age,$home)
    {
        parent::__construct($name,$age);
        $this->home = $home;
    }

    public function getInfo()
    {
        echo "这是子类的get<br>";
        echo "name:".$this->name."|age".$this->age."|money:".$this->money."<br>";
    }

    public function demo()
    {
        parent::demo();
        echo "FUNK!!!!";
    }
}

echo "<pre>";
//实例化
$user = new User(‘张三‘,10);
$vip = new VipUser(‘李四‘,‘11‘,‘新疆‘);
var_dump($user);
var_dump($vip);
$user->getInfo();
$vip->getInfo();
$vip->demo();

　　

　　输出结果: