如何从父类获取子类中变量的值

Question

这是我得到的错误：

致命错误：无法在第3行的C：\\ xampp \\ htdocs \\ test \\ home.php中保留'Parent'作为类名

这是我的代码：

<?php
    class Parent{
      public $num1 = 3;
    }
    class Child extends Parent{
        public $sum = 2 + $this->num1;
    }
    $obj = new Child();
    echo $obj->sum;
    ?>

Answer 1

不能使用Parent作为一个类的名字，你可以为$sum使用初始值$sum = 2 + $this->num1; 。

// renamed parent class
class ParentClass {
   public $num1 = 3;
}

// renamed child class
class ChildClass extends ParentClass {
    public $sum ;

    // a constructor is where you would do this type of math
    function __construct() {
        $this->sum = 2 + $this->num1;
    }
}

// create your child object
$obj = new ChildClass();
echo $obj->sum;

Answer 2

您以错误的方式定义了变量，该变量应为var $ num = 3;

class Parent{
      var $num1 = 3;
    }
    class Child extends Parent{
        public function sum() { 
         return 2 + $this->num1;
    }
    }
    $obj = new Child();
    echo $obj->sum();