php中public,private,protected属性的定义、用法、区别实例详解

<?php
class BaseClass {
  public $public = 'public';
  private $private = 'private';
  protected $protected = 'protected';
  function construct(){
  }
  function print_var(){
    print $this->public;echo '<br />';
    print $this->private; echo '<br />';
    print $this->protected; echo '<br />';
  }
}

class Subclass extends BaseClass {
  // public $public = 'public2';
  protected $protected ='protected2';
  function construct(){
    echo $this->protected;//可以访问，因为类中定义为受保护的，所以在本类或子类中可以，子类中还可以重复付值
    echo '<br />';
    echo $this->private;//error 因为是私有的只有在定义她的类baseclass中可以用
  }
}
  $obj1 = new BaseClass();
  $obj1->print_var();
  //echo $obj1->protected;//error 因为是受保护的，只有在本类内部或子类父类中可以调用
  //echo $obj1->private;//error 同上私有的，只有在本类内调用
  echo $obj1->public;
  echo "<hr />";
  $obj2 = new Subclass();
  echo '<br />';
  echo $obj2->public;echo '<br />';
  echo $obj2->protected;
  //echo $obj2->private;//error
  //echo $obj2->protected;//error
?>