php class中public,private,protected的区别以及实例分析

一,public,private,protected的区别
public:权限是最大的,可以内部调用,实例调用等。
protected: 受保护类型,用于本类和继承类调用。
private: 私有类型,只有在本类中使用。

二,实例

复制代码 代码如下:


<?php
error_reporting(E_ALL);
class test{
 public $public;
 private $private;
 protected $protected;
 static $instance;
 public&nbsp; function __construct(){
 $this->public&nbsp;&nbsp;&nbsp; = 'public&nbsp;&nbsp;&nbsp;&nbsp; <br>';
 $this->private&nbsp;&nbsp; = 'private&nbsp;&nbsp;&nbsp; <br>';
 $this->protected = 'protected&nbsp; <br>';
 }
 static function tank(){
 if (!isset(self::$instance[get_class()]))
 {
 $c = get_class();
 self::$instance = new $c;
 }
 return self::$instance;
 }&nbsp;&nbsp; &nbsp;
 public function pub_function() {
 echo "you request public function<br>";
 echo $this->public;
 echo $this->private;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; //private,内部可以调用
 echo $this->protected;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; //protected,内部可以调用
 $this->pri_function();&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; //private方法,内部可以调用
 $this->pro_function();&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; //protected方法,内部可以调用
 }
 protected&nbsp; function pro_function(){
 echo "you request protected function<br>";
 }
 private function pri_function(){
 echo "you request private function<br>";
 }
}
$test = test::tank();
echo $test->public;
echo $test->private;&nbsp;&nbsp;&nbsp; //Fatal error: Cannot access private property test::$private
echo $test->protected;&nbsp; //Fatal error: Cannot access protected property test::$protected
$test->pub_function();
$test->pro_function();&nbsp; //Fatal error: Call to protected method test::pro_function() from context
$test->pri_function();&nbsp; //Fatal error: Call to private method test::pri_function() from context
?>


从上面的例子中,我们可以看出,
public:    可以class内部调用,可以实例化调用。
private:   可以class内部调用,实例化调用报错。
protected:  可以class内部调用,实例化调用报错。

复制代码 代码如下:


<?php
class test{
 public $public;
 private $private;
 protected $protected;
 static $instance;
 public&nbsp; function __construct(){
 $this->public&nbsp;&nbsp;&nbsp; = 'public&nbsp;&nbsp;&nbsp;&nbsp; <br>';
 $this->private&nbsp;&nbsp; = 'private&nbsp;&nbsp;&nbsp; <br>';
 $this->protected = 'protected&nbsp; <br>';
 }
 protected function tank(){&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; //私有方法不能继承,换成public,protected
 if (!isset(self::$instance[get_class()]))
 {
 $c = get_class();
 self::$instance = new $c;
 }
 return self::$instance;
 }&nbsp;&nbsp; &nbsp;
 public function pub_function() {
 echo "you request public function<br>";
 echo $this->public;
 }
 protected&nbsp; function pro_function(){
 echo "you request protected function<br>";
 echo $this->protected;
 }
 private function pri_function(){
 echo "you request private function<br>";
 echo $this->private;
 }
}
class test1 extends test{
 public function __construct(){
 parent::tank();
 parent::__construct();
 }
 public function tank(){
 echo $this->public;
 echo $this->private;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; //Notice: Undefined property: test1::$private
 echo $this->protected;
 $this->pub_function();
 $this->pro_function();
 $this->pri_function();&nbsp;&nbsp;&nbsp; //Fatal error: Call to private method test::pri_function() from context 'test1'
 }
 public&nbsp; function pro_extends_function(){
 echo "you request extends_protected function<br>";
 }
 public function pri_extends_function(){
 echo "you request extends_private function<br>";
 }
}
error_reporting(E_ALL);
$test = new test1();
$test -> tank();&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; //子类和父类有相同名字的属性和方法,实例化子类时,子类的中的属性和方法会盖掉父类的。
?>


从上面的例子中,我们可以看出,
public:    test中的public可以被继承。
private:   test中的private不可以被继承。
protected:test中的protected可以被继承。
static:   test中的static可以被继承。
唉,对于这些东西,老是不喜欢记着,用的时候,总感觉不对,又要去查,所以写个例子,方便自己查看。

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