PHP面向對象構造函數說明

本文不再贅述面向對象的知識，本文着重說明PHP的構造函數。
php類的構造函數可以是魔術魔方__construct() 也可以是和類同名的函數，實例如下：

 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，在繼承時，應該注意的是：
【子類可以不寫構造函數，那麼使用父類的構造函數】

 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();

【子類如果寫了構造函數，那麼不會再調用父類的構造函數了】

 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

【父類的構造函數如果是私有的，可以被繼承，但是子類必須有自己的構造函數，並且明確寫出來】

 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