OOP面向对象基础-继承

class Person
{
    public $name='zz';
    private $age=18;
    public function say(){
        echo $this->name;
    }
}
class A extends Person
{
//    private $name='xx';//直接爆红
    public $age='19';
    public function say(){
        echo "age:".$this->age;
    }
}

$a = new A;
echo $a->say();

class Person
{
    private $name='cc';
    public $age;
    public function say(){
        echo $this->name;
    }
    public function __construct(){
        echo "this is a ".$this->name;
    }
}

class A extends Person
{
    const BIRTH = '1125';
    private $sex = '女';
    public function __construct(){
        parent::__construct();//调用父类的构造方法
        echo self::BIRTH;//1125
    }
}

$a = new A;
$a->say();

class Num
{
    public $a = 10;
    public function plus($num){
        $this->a =$this->a+$num;
        return $this->a;
    }
    public function plus1($num){
        $this->a =$this->a+$num;
        return $this;
    }
}

$a  = new Num();
var_dump($a->plus(12));///返回int(22)
var_dump($a->plus1(12));//object(Num)#1 (1) { ["a"]=> int(34) }

var_dump($a->plus1(10)->plus1(10)->plus(10));// 最后输出就好 int(64)