（进阶篇）PHP面向对象三大特点学习(封装、继承、多态)

<?php 
class Person{ 
    public $name; 
    protected $age; 
    private $salary; 
    function __construct($name,$age,$salary){ 
        $this->name=$name; 
        $this->age=$age; 
        $this->salary=$salary; 
    } 
    public function showinfo(){ 
        //这表示三个修饰符都可以在本类内部使用 
        echo $this->name."||".$this->age."||".$this->salary; 
    } 
} 
$p1=new Person('张三',20,3000); 
//这里属于类外部，那么如果用下面的方法访问age和salary都会报错 
// echo $p1->age; echo$p1->salary; 
?>

public function setxxxx($val){ 
    $this->xxxx=$val; 
} 
public function getxxxx(){ 
    return $this->xxxx; 
}

public function getsalary(){ 
    return $this->salary; 
    //扩展：这里可以调用一些方法，如判断用户名等，正确才给访问 
}

<?php 
class testa{ 
    protected $name; 
    //使用__set()来管理所有属性 
    public function __set($pro_name,$pro_val){ 
        //上面$pro_name和$pro_val可自定义 
        //下面$this->pro_name为既定，不可更改 
        $this->pro_name=$pro_val; 
    } 
    //使用__get()来获取所有属性值 
    public function __get($pro_name){ 
        if(isset($pro_name)){ 
            return $this->pro_name; 
        } else { 
            return null; 
        } 
    } 
} 
$n1=new testa(); 
//正常情况，类外部是不能访问protected属性的，
但是用了上面的方法就可以对它们进行操作 
$n1->name='小三'; 
echo $n1->name; 
?>

<?php 
class Pupil{ 
    public $name; 
    protected $age; 
    public function getinfo(){ 
        echo $this->name.'||'.$this->age; 
    } 
    public function testing(){ 
        echo 'this is pupil'; 
    } 
} 
class Graduate{ 
    public $name; 
    protected $age; 
    public function getinfo(){ 
        echo $this->name.'||'.$this->age; 
    } 
    public function testing(){ 
        echo 'this is Graduate'; 
    } 
} 
?>

<?php 
class Students{ 
    public $name; 
    public $age; 
    public function __construct($name,$age){ 
        $this->name=$name; 
        $this->age=$age; 
    } 
    public function showinfo(){ 
        echo $this->name.'||'.$this->age; 
    } 
} 
class Pupil extends Students{ 
    function testing(){ 
        echo 'Pupil '.$this->name.' is testing'; 
    } 
} 
class Graduate extends Students{ 
    function testing(){ 
        echo 'Graduate '.$this->name.' is testing'; 
    } 
} 
$stu1=new Pupil('张三',20); 
$stu1->showinfo(); 
echo '<br/>'; 
$stu1->testing(); 
?>

class 父类名{} 
class 子类名 extends 父类名{}

<?php 
class A{ 
    public $name='AAA'; 
} 
class B extends A{ 
    public $age=30; 
} 
class C extends B{} 
$p=new C(); 
echo $p->name;//这里会输出AAA 
?>

class A{ 
    public function __construct(){ 
        echo 'A'; 
    } 
} 
class B extends A{ 
    public function __construct(){ 
        echo 'B'; 
    } 
} 
$b=new B();//这里会优先输出B中的构造方法，

class A{ 
    public function test(){ 
        echo 'a_test'; 
    } 
} 
class B extends A{ 
    public function __construct(){ 
        //两种方法都行 
        A::test(); 
        parent::test(); 
    } 
} 
$b=new B();

<?php 
class Animal{ 
    public $name; 
    public $price; 
    function cry(){ 
        echo 'i don\'t know'; 
    } 
} 
class Dog extends Animal{ 
    //覆盖、重写 
    function cry(){ 
        echo 'Wang Wang!'; 
        Animal::cry();//这里不会报错，能正确执行父类的cry(); 
    } 
} 
$dog1=new Dog(); 
$dog1->cry(); 
?>

父类private function cry(){} 子类 protected function cry(){} 可以正确执行