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HomeBackend DevelopmentPHP TutorialPHP的构造方法,析构方法和this关键字详细介绍_php技巧

一.什么是构造方法
    构造方法是类的一种特殊的方法,它的主要作用是完成对新对象初始化.
    特点:
1.    没有返回值.
2.    在创建一个新的对象时,系统会自动调用该类的构造方法完成对新对角的初始化.
    语法:
    php5:        修饰符 function __construct()

                        {
                            //code

                        }
    php4:        修饰符 function 类名()

                        {
                            //code

                        }
注意:
   1. php5里对两者都支持,如果两种构造方法同时存在的话,优先选择第一种.
   2. 一个类里面默认有一个不带参数为空的构造方法,一旦自定义了一个构造方法,就会覆盖默认的构造方法.

      所以说一个类有且只有一个构造方法.
   3.一个类只能有一个构造方法.(不能重载)
   4.构造方法默认的访问修饰符为public.
二.this关键字
    this代表当前对象.可以理解为:谁调用它,它就代表谁.
    注意事项:
    this不在类定义的使用,只能在类定义的方法中使用.
三.实例

复制代码 代码如下:

    header("Conter-Type:text/html;charset=utf-8");
    class Person
    {
        public $name;  //成员变量
        public $age;

       // function __construct()
        //{
          //  echo "不带参数的构造方法";

        //}
        function __construct($name,$age)
        {
            $this -> name = $name;
            $this -> age = $age;
            echo "带参数的构造方法"."
";
        }
        //成员方法
        function view()
        {
            //this的引用.
            echo "姓名:".$this ->name.", 年龄:".$this ->age;

        }
    }
        //new一个新的对象
    //$p = new Person();
    $p2 = new Person("李四",13);
    $p2 ->view();
?>

结果如下:
    带参数的构造方法

复制代码 代码如下:

    姓名:李四, 年龄:13

四:析构方法:
    析构方法是PHP5引入的新概念.主要作用:释放资源(比如:释放数据库链接,图片资源...).
    语法:
    function __destruct(){}
    特点:

    1.析构方法没有返回值.

    2.主要作用是释放资源.并不是销毁对象本身.
    3.在销毁对象前,系统自动调用该类的析构方法.

    4.一个类最多只有一个析构方法.

五:例子:

复制代码 代码如下:

    header("Conter-Type:text/html;charset=utf-8");

    class Person
    {
        public $name;
        public $age;
        //构造方法
        function __construct($name,$age)
        {
            $this ->name = $name;
            $this ->age = $age; 

        }
        //析构方法
        function __destruct()
        {
            echo "姓名:".$this->name.", 年龄".$this->age."-->销毁
";
        }

    }

    $p1= new Person("小一",18);
    $p2= new Person("小二",17);
?>

结果:
    姓名:小二, 年龄17-->销毁
    姓名:小一, 年龄18-->销毁

分析结论:
    1.析构方法会自动调用.

    2.析构方法调用的顺序是先创建的对象后被销毁.

    3.当一个对象没有引用,被垃圾回收机制确认为垃圾时,调用析构方法.

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