如何将公共值从父 class 传递给 PHP 中的子 class？

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.

Answer 1

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.