Difference: 1. If a class member is declared as public, it can be accessed from anywhere; and if a class member is declared as private, it can only be accessed by the class that defines the member. 2. Public is a public type with the greatest authority and can be called internally, instance called, etc.; private is a private type and can only be used in this class.
The operating environment of this tutorial: Windows 7 system, PHP version 7.1, DELL G3 computer
public, private and protected are called access modifiers . Just like C, PHP also has three access modifiers such as public, private and protected. The visibility of a property, method or constant can be defined by preceding the declaration with these keywords.
1. If a class member is declared public, it can be accessed from anywhere.
Public has the greatest authority and can make internal calls, instance calls, etc.
2. If a class member is declared protected, it can only be accessed within the class itself and in inheritance and parent classes.
protected is a protected type, used for calling this class and inherited classes.
3. If a class member is declared private, it can only be accessed by the class that defines the member.
private is a private type and can only be used in this class.
Example:
<?php
error_reporting(E_ALL);
class test{
public $public;
private $private;
protected $protected;
static $instance;
public function __construct(){
$this->public = 'public <br>';
$this->private = 'private <br>';
$this->protected = 'protected <br>';
}
static function tank(){
if (!isset(self::$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 inside the class and can be instantiated ization call.
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.
<?php
class test{
public $public;
private $private;
protected $protected;
static $instance;
public function __construct(){
$this->public = 'public <br>';
$this->private = 'private <br>';
$this->protected = 'protected <br>';
}
protected function tank(){ //私有方法不能继承，换成public,protected
if (!isset(self::$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 'test1'
}
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:
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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