不在对象上下文php时使用$ this

Question

I just started learning OOPS in php. I wrote a simple program for implementing inheritance. I am getting a fatal error of $this when not in object context. Can anyone explain me this error, what does it mean? here is my code:

<?php

    class human{

        public $gender;

        public function _construct($gender)
        {
            $this->gender=$gender;

            echo $this->get_gender();
        }

        public function get_gender()
        {
            return $this->gender;
        }


    }

    class person extends human{

        public $name;
        public $surname;

        public static function set_name($name)
        {
            $this->name=$name;
        }
        public static function set_surname($surname)
        {
            $this->surname=$surname;
        }

        public static function get_name()
        {
            return $this->name;
        }
        public static function get_surname()
        {
            return $this->surname;
        }
    }

    $john = new person('male');
    $john->set_name('John');
    $john->set_surname('Williams');
    echo $john->get_name().' '.$john->get_surname().'is a '.$john->get_gender();
    ?>

Answer 1

There are two problems here:

1. You have defined your methods as static. You should not do that as they are not, they depend on being called on an object as you want to use the objects non-static properties.

2. You have a typo in your constructor function. The correct name for the constructor is __construct, notice the two _ at the beginning.