如何解决未定义变量和未定义属性警告？

Question

I have $name and $age defined in set_name() and set_age . Please check index.php:

<?php
// This part needs some fixing.
class Pet {
    public $name;
    public $age;    

    // get() and set() functions for name
    function set_name($name) {
        $this->name = $name;
    }
    function get_name() {
        return $this->$name;
    }

    // get() and set() functions for age
    function set_age($age) {
        $this->age = $age;
    }
    function get_age() {
        return $this->$name;
    }
}
.....

Edit: This problem is fixed. No need for new answers!

Answer 1

You need constructor for your classes and don't do the makeSound method in your Pet class static . Try this:

public Cat(){
  makeSound(sound);
}

public Dog(){
  makeSound(sound);
}

Answer 2

Your method declaration is wrong. If a parent has an implemented version of a function, you do not need to declare it in the subclass. But even if you would want to, the correct way to do it (thus overriding the parent function) would be:

void makeSound(String sound) {
        System.out.println("Hi, I make a " + sound);
    }

The use of a static keyword would not make much sense. A static method is a method that is part of the class and not of the created objects. Meaning you could call the method like this Pets.makeSound(...)