From a usage standpoint, what's the difference between a private and protection class function?

Question

I know the manual definition, but from a real life usage standpoint, what's the difference? When would you use one over the other?

Answer 1

EDIT: use protected methods when you want a child class (one that extends your current (or parent) class) to be able to access methods or variables within the parent.

Here is the PHP Visibility Manual

private can be seen by no other classes except the one the variable/method is contained in.

protected can be seen by any class that is in the same package/namespace.

Code from the manual.

<?php
/**
 * Define MyClass
 */
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; // Works
echo $obj->protected; // Fatal Error
echo $obj->private; // Fatal Error
$obj->printHello(); // Shows Public, Protected and Private


/**
 * Define MyClass2
 */
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; // Works
echo $obj2->private; // Undefined
echo $obj2->protected; // Fatal Error
$obj2->printHello(); // Shows Public, Protected2, Undefined

?>