OOP -> Modifiers

Modifier =  visibility = Access Level of data member or Member function.

Modifier play very vital rule in any class.
Becuase
Some property all can acess - Public
Some property only relevant person can acess - Protected
Some property only you  can access - Private

Therefore Modifiers are three types
a) Public
b) Protected
c) Private

Data member can be three types public, protected OR private
Member function can be three types public, protected OR private.

Data Member refer to class variable.
Member function refer to class function.

Example1:

class MyClass
{
    public $public = 'Public';
    protected $protected = 'Protected';
    private $private = 'Private';

    function printHello()
    {
        echo $this->public;
        echo $this->protected;
        echo $this->private;
    }
}

$obj = new MyClass();
echo $obj->public; // It will be Works
echo $obj->protected; // Fatal Error becuase you cannot access protected in this way
echo $obj->private; // Fatal Error becuase you cannot access protected in this way
$obj->printHello(); // Shows Public, Protected and Private data meber values

Example 2:

class MyClass2 extends MyClass
{
    // We can redeclare the public and protected method, but not private
    protected $protected = 'Protected2';

    function printHello()
    {
        echo $this->public;
        echo $this->protected;
        echo $this->private;
    }
}

$obj2 = new MyClass2();
echo $obj2->public; // It will be Work
echo $obj2->private; // Undefined becuase private variable can not be inherit
echo $obj2->protected; // Fatal Error becuase protected can be used within function only
$obj2->printHello(); // Shows Public, Protected2, Undefined