Home Backend Development PHP Tutorial PHP中__construct(),类的构造函数详解

PHP中__construct(),类的构造函数详解

Jun 13, 2016 am 11:49 AM
php

PHP中把以两个下划线__开头的方法称为魔术方法(Magic methods),这些方法在PHP中充当了举足轻重的作用。

__construct(),类的构造函数

php中构造方法是对象创建完成后第一个被对象自动调用的方法。在每个类中都有一个构造方法,如果没有显示地声明它,那么类中都会默认存在一个没有参数且内容为空的构造方法。

1、 构造方法的作用

通常构造方法被用来执行一些有用的初始化任务,如对成员属性在创建对象时赋予初始值。

2、 构造方法的在类中的声明格式

function __constrct([参数列表]){
    方法体 //通常用来对成员属性进行初始化赋值
}
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3、 在类中声明构造方法需要注意的事项

1、在同一个类中只能声明一个构造方法,原因是,PHP不支持构造函数重载。

2、构造方法名称是以两个下画线开始的__construct()

下面是它的例子:

<?php
    class Person
    {                                                                      
            public $name;        
            public $age;        
            public $sex;        
                                                                 
        /**
         * 显示声明一个构造方法且带参数
         */                                                                                       
        public function __construct($name="", $sex="男", $age=22)
        {      
            $this->name = $name;
            $this->sex = $sex;
            $this->age = $age;
        }
        
        /**
         * say 方法
         */
        public function say()
        { 
            echo "我叫:" . $this->name . ",性别:" . $this->sex . ",年龄:" . $this->age;
        }   
                                                                                           
    }
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创建对象$Person1且不带任参数

$Person1 = new Person();
echo $Person1->say(); //输出:我叫:,性别:男,年龄:27
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创建对象$Person2且带参数“小明”

$Person2 = new Person("小明");
echo $Person2->say(); //输出:我叫:张三,性别:男,年龄:27
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创建对象$Person3且带三个参数

$Person3 = new Person("李四","男",25);
echo $Person3->say(); //输出:我叫:李四,性别:男,年龄:25
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