Detailed explanation of the definition and usage of PHP object-oriented programming classes

<?php
class Person {
  private $name;
  private $sex;
  private $age;
  function __construct($name = "", $sex = "男", $age = 22) {
    $this->name = $name;
    $this->sex = $sex;
    $this->age = $age;
  }
  // 直接为私有属性赋值时自动调用，可以屏蔽一些非法赋值
  // 之前有版本可以设置方法为private function __set()
  // The magic method __set() must have public visibility
  // 因为5.35对魔术方法限制的严格了
  public function __set($propertyName, $propertyValue) {
    if ($propertyName == "sex") {
      if (! ($propertyValue == "男" || $propertyValue == "女")) {
        return;
      }
      if ($propertyValue > 150 || $propertyValue < 0) {
        return;
      }
    }
    // 根据传入的成员属性名,赋上相应的值
    $this->$propertyName = $propertyValue;
  }
  // 用来获取私有属性
  public function __get($propertyName) {
    if (isset ( $this->$propertyName )) {
      return ($this->$propertyName);
    } else {
      return (NULL);
    }
  }
  public function __isset($propertyName) {
    if ($propertyName == "name") {
      return false; // 返回假，不允许在对象外部测定这个属性
    }
    return isset ( $this->$propertyName );
  }
  public function __unset($propertyName) {
    if($propertyName=="name") {
      return; //不允许删除name属性
    }
    unset($this->$propertyName);
  }
  function say() {
    echo $this->name . "在说话<br/>";
  }
  function run() {
    echo "在走路·<br/>";
  }
  function __destruct() {
    echo "goodbye" . $this->name . "<br/>";
  }
}
$person1 = new Person ();
$person2 = new Person ( "2" );
$person3 = new Person ( "3" );
// 自动调用了__set()
$person1->name = "张三";
echo $person1->name;
echo "<br/>";
echo $person1->say ();
// 自动调用了__get()
echo $person1->age;
echo "<br/>";
var_dump ( isset ( $person1->name ) );
echo "<br/>";
unset($person1->name);
echo "unset------------>".$person1->name;//name 没有被unset()
echo "<br/>";
$person2 = null;
?>

张三
张三在说话
22
bool(false)
unset------------>张三
goodbye2
goodbye3
goodbye张三