PHP 객체지향 프로그래밍에서 OOP 상속 사용법에 대한 자세한 설명

<?php
class Person {
  var $name;//protected
  var $sex;
  var $age;
  function __construct($name = "", $sex = "男", $age = 22) {
    $this->name = $name;
    $this->sex = $sex;
    $this->age = $age;
  }
  function say() {
    echo $this->name . "在说话<br/>";
  }
  function run() {
    echo "在走路·<br/>";
  }
}
class Student extends Person {
  var $school;
  function __construct($name = "", $sex = "男", $age = 22,$school="") {
    parent::__construct($name,$sex,$age);
    $this->school = $school;
  }
  function study() {
    echo $this->name."正在".$this->school."学习<br/>";
  }
}
class Teacher extends Student {
  var $wage;
  function teaching() {
    echo $this->name."正在".$this->school."教学，每月工资为".$this->wage."<br/>";
  }
}
$teacher1 = new Teacher("kaifu","男",22);
$teacher1->school = "edu";
$teacher1->wage = 4000;
$teacher1->say();
$teacher1->study();
$teacher1->teaching();
?>

kaifu在说话
kaifu正在edu学习
kaifu正在edu教学，每月工资为4000