How to pass public value from parent class to child class in PHP?

Question

I just learn deeper about OOP in PHP, but not an expert yet. I'm still a beginner. I have a problem. I want to pass the public value from parent class to child class. But I cant get it. I tried to find the answer in google and stackoverflow, and I have tried to follow the instruction, but it didnt work.

My code is like below:

class A
{
    public $arrayperk;
    public $nilai;
    
    function __construct()
        {
            $this->nilai='This is bad';
        }
    function testParent()
        {
            return $this->arrayperk;
        }
    function testA()
        {
            return number_format(1000); 
        }
}

class B extends A
{
    function  coba()
        {
            return $this->testParent();
        }
    function  coba2()
        {
            return $this->testA();
        }
    function coba3()
        {
            return $this->nilai;
        }
}

The problem is that I want to pass the value of $arrayperk to the function inside class B. But it did not work at all.

My code is like below:

$arrayperk=Array( 1 => 'array1', 2 => 'array2');
$class_a=new A();
$class_a->arrayperk=$arrayperk;
$class_b=new B();

print_r($class_a->testParent()); //return array as needed.
print_r($class_b->coba()); //return nothing although it calls the parent class, and the parent work correctly if it is called like above. This is what I want to get and the problem I face.
echo $class_b->coba2(); //return 1,000 and it access the parent function
echo $class_b->coba3(); //return This is bad as written at parent class.

As you can see, the problem is at

$class_b->coba()

It gives nothing even I have call it correctly to the parent class, but the other test works fine when accessing the parent class function.

I am even unable to pass $this->arrayperk inside class B. It returns nothing. What am I missing? I cant get both $this->arrayperk and a function inside parent class.

Please help. Thanks.

Simeon Borisov · Answer

You're instantiating 2 different classes, $class_a and $class_b. Your're only setting the $arrayperk for $clas_a

$class_a=new A();
$class_a->arrayperk=$arrayperk;
$class_b=new B();

here when $class_b is instantiated, you don't give it any properties. A simple fix would be to just assign the property:

$class_b->arrayperk = $arrayperk;

Even though you're inheriting the parent method, the actual property $arrayperk, in your case, is empty so you need to set it for each instance individually.

Inheritance means you inherit the methods of the parent class, but each instance behaves as a separate unit.

If you do

$class_c = new B();
var_dump($class_c->arrayperk);

This value would also end up being NULL

Also helps if you var_dump your values, instead of printing, since in this case you would see the value of arrayperk is NULL.

How to pass public value from parent class to child class in PHP?

1 Answers