异常类中的php父构造函数

Question

于是又在看PHP手册，看到一个自定义异常调用父异常构造函数的代码的注释，不明白这样做的目的。

这是代码:

class MyException extends Exception
{
        // Redefine the exception so message isn't optional
        public function __construct($message, $code = 0) {
        // some code

        // make sure everything is assigned properly
        parent::__construct($message, $code);
    }

    // custom string representation of object
    public function __toString() {
    return __CLASS__ . ": [{$this->code}]: {$this->message}\n";
    }

    public function customFunction() {
        echo "A custom function for this type of exception\n";
    }
}

我不明白以下逻辑:

//make sure everything is assigned properly
parent::__construct($message, $code);

关于为什么这样做的任何逻辑都会有所帮助。

Answer 1

异常类包含自己的属性，例如 $code和 $message
它们受子类的影响，例如:

class Exception {
  protected $code ;
  protected $message ;

  public function __construct($code, $message){
    $this->code = $code ;
    $this->message = $message ;

    //AND some important default actions are performed
    //when class is instantiated.
  }
}

因此，在您调用 parent::__construct() 之后

您的子类将具有实例变量 $code和 $message正确设置。

$myEx = new MyException("10", "DB Error") ;
//Now you can get the error code, because it was set in its parent constructor:
$code = $myEx->getCode() ;