PHP面向对象构造函数说明

本文不再赘述面向对象的知识，本文着重说明PHP的构造函数。
php类的构造函数可以是魔术魔方__construct() 也可以是和类同名的函数，实例如下：

 class A{
    public function A(){
        echo ‘A is constructing...‘;
    } 
 }
 class B{
    public function __construct(){
        echo ‘B is contructing...‘;
    }
 }

 $a = new A();   // A is constructing...
 $b = new B();   // B is constructing...

此外，在继承时，应该注意的是：
【子类可以不写构造函数，那么使用父类的构造函数】

 class A{
    protected $name;
    public function A(){
        echo ‘A is constructing...<br>‘;
    }
    public function set_name($name){
        $this->name = $name;
    }
    public function get_name(){
        return $this->name;
    }
 }
 class B extends A{

    /*
    public function __construct(){
        echo ‘B is contructing...<br>‘;
    }
    */

 }

 //$a = new A();
 $b = new B();  // A is constructing...
 $b->set_name(‘zhangsan‘);
 echo $b->get_name();

【子类如果写了构造函数，那么不会再调用父类的构造函数了】

 class A{
    protected $name;
    public function A(){
        echo ‘A is constructing...<br>‘;
    }
    public function set_name($name){
        $this->name = $name;
    }
    public function get_name(){
        return $this->name;
    }
 }
 class B extends A{

    public function __construct(){
        echo ‘B is contructing...<br>‘;
    }

 }

 //$a = new A();
 $b = new B(); // just echo ‘B is contructing...‘
 $b->set_name(‘zhangsan‘);
 echo $b->get_name(); // zhangsan

【父类的构造函数如果是私有的，可以被继承，但是子类必须有自己的构造函数，并且明确写出来】

 class A{
    protected $name;
    private function A(){
        echo ‘A is constructing...<br>‘;
    }
    public function set_name($name){
        $this->name = $name;
    }
    public function get_name(){
        return $this->name;
    }
 }
 class B extends A{

    public function __construct(){
        echo ‘B is contructing...<br>‘;
    }

 }

 //$a = new A();
 $b = new B(); // B is contructing...
 $b->set_name(‘zhangsan‘);
 echo $b->get_name();  // zhangsan