Usage examples and difference analysis of public, private and protected

1. The difference between public, private and protected

public: has the greatest permissions and can be called internally, instance called, etc.
protected: Protected type, used for this class and inherited class calls.
private: Private type, only used in this class.

2, Example

The code is as follows:

<?php
error_reporting
(E_ALL);
class test{
 public $public;
 private $private;
 protected $protected;
 
static
 $instance;
 public  function construct(){
 $this->public    = &#39;public     <br>&#39;;
 $this->private   = &#39;private    <br>&#39;;
 $this->protected = &#39;protected  <br>&#39;;
 }
 static function tank(){
 if (!isset(self::$instance[get_class()]))
 {
 $c = get_class();
 self::$instance = new $c;
 }
 
return  self::$instance;
 }    
 public function pub_function() {
 echo "you request public function<br>";
 echo $this->public;
 echo $this->private;        //private,内部可以调用
 echo $this->protected;      //protected,内部可以调用
 $this->pri_function();      //private方法，内部可以调用
 $this->pro_function();      //protected方法，内部可以调用
 }
 protected  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 $test->private;    //Fatal error: Cannot access private property test::$private
echo $test->protected;  //Fatal error: Cannot access protected property test::$protected
$test->pub_function();
$test->pro_function();  //Fatal error: Call to protected method test::pro_function() from context
$test->pri_function();  //Fatal error: Call to private method test::pri_function() from context
?>

From the above example, we can see ,
public: Can be called internally in a class or instantiated.
private: Can be called inside the class, and an error will be reported when instantiating the call.
protected: It can be called inside the class, and an error will be reported when instantiating the call.

The code is as follows:

<?php
class test{
 public $public;
 private $private;
 protected $protected;
 static $instance;
 public  function construct(){
 $this->public    = &#39;public     <br>&#39;;
 $this->private   = &#39;private    <br>&#39;;
 $this->protected = &#39;protected  <br>&#39;;
 }
 protected function tank(){                          //私有方法不能继承，换成public,protected
 if (!isset(self::$instance[get_class()]))
 {
 $c = get_class();
 self::$instance = new $c;
 }
 return self::$instance;
 }    
 public function pub_function() {
 echo "you request public function<br>";
 echo $this->public;
 }
 protected  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 $this->private;       //Notice: Undefined property: test1::$private
 echo $this->protected;
 $this->pub_function();
 $this->pro_function();
 $this->pri_function();    //Fatal error: Call to private method test::pri_function() from context &#39;test1&#39;
 }
 public  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();       //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。
?>

From the above example, we can see that
public: public in test can be inherited.
private: Private in test cannot be inherited.
protected: protected in test can be inherited.
static: static in test can be inherited.

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