{php 初学头疼问题之：PHP5中的public，private和protected}

<?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 $obj->public; // Works
echo $obj2->private; // Undefined
echo $obj2->protected; // Fatal Error
$obj2->printHello(); // Shows Public, Protected2, not Private

?>

public 相当于Var声明的~~整个页面随时可以修改 
private 只能在所属类中操作. 
protected 有继承关系的类内都可操作. 
……我就这样理解.