1. 请实例演绎你对面向对象类与对象关系的理解？ 2. 请实例演绎oop的封装性是怎么实现的？ 3. 请实例演绎构造函数的作用有哪些？

<?php
class people {
    public $name;// 姓名
    public $gender; //性别
    protected $age; //年龄
    private $birthday; //生日
    public function __construct($name,$gender,$age,$birthday)
    {
        $this->name = $name;
        $this->gender = $gender;
        $this->age = $age;
        $this->birthday = $birthday;
    }
    public function say()
    {
        return "大家好我是{$this->name},我是一个{$this->gender}孩 <br>";
    }
    public function speak(){
        return "我今年{$this->age}岁 我的生日是{$this->birthday}";
    }
}
$obj = new people('小明','男',13,'2008.05.06');
echo $obj->say();
echo $obj->speak();
$obj->name='小红';
$obj->gender ='女';
echo $obj->say();
echo $obj->speak();