PHP中的public、private和protected有什么区别（） _PHP访问修饰符

public、private和protected称为访问修饰符。与C++一样, PHP也具有三个访问修饰符, 例如public, private和protected。属性, 方法或常量的可见性可以通过在声明的前面加上这些关键字来定义。

如果类成员声明为public, 则可以在任何地方访问它。
如果将类成员声明为protected, 则只能在类本身内部以及通过继承和父类访问它。
如果类成员声明为private, 那么只有定义该成员的类才能访问它。

public访问修饰符：
该修饰符可以在类的内部和外部使用。
例子：

< ?php//BaseClass class pub { public $tag_line = "A Computer Science Portal for Geeks!" ; function display() { echo $this -> tag_line. "< br/> " ; } }//SubClass class child extends pub { function show(){ echo $this -> tag_line; } } //Object Declaration $obj = new child; //A Computer Science Portal for Geeks! echo $obj -> tag_line. "< br/> " ; //A Computer Science Portal for Geeks! $obj -> display(); //A Computer Science Portal for Geeks! $obj -> show(); ?>

输出如下：

A Computer Science Portal for Geeks! A Computer Science Portal for Geeks! A Computer Science Portal for Geeks!

protected访问修饰符：该修饰符可以在定义它的类及其父类或继承的类中使用。
例子：

< ?php//Base Class class pro { protected $x = 500; protected $y = 500; //Subtraction Function function sub() { echo $sum = $this -> x- $this -> y . "< br/> " ; } } //SubClass - Inherited Class class child extends pro { function mul() //Multiply Function { echo $sub = $this -> x* $this -> y; } } $obj = new child; $obj -> sub(); $obj -> mul(); ?>

【PHP中的public、private和protected有什么区别（）】输出如下：

0 250000

private访问修饰符：该修饰符可以在定义它的类中使用。 (无法在继承的类中的类外部访问)。
例子：

< ?php//Base Class class demo { private $name = "A Computer Science Portal for Geeks!" ; private function show() { echo "This is private method of base class" ; } } //Sub Class class child extends demo { function display() { echo $this -> name; } } //Object Declaration $obj = new child; //Uncaught Error: Call to private method demo::show() $obj -> show(); //Undefined property: child::$name $obj -> display(); ?>

输出如下：

It will display error because private class data can not be accessed outside the class

其他示例：
例子：

< ?php class BaseClass { public $public = 'Public' ; protected $protected = 'Protected' ; private $private = 'Private' ; function Display() { echo $this -> public ; echo $this -> protected ; echo $this -> private ; } }$obj = new BaseClass(); echo $obj -> public ; echo $obj -> protected ; //Cannot access protected property echo $obj -> private ; //Cannot access private property $obj -> Display(); //Displays all propertiesclass SubClass extends BaseClass { public $public = 'Public Sub Class' ; protected $protected = 'Protected Sub Class' ; function Display() { echo $this -> public ; echo $this -> protected ; echo $this -> private ; } }$obj2 = new SubClass(); echo $obj2 -> public ; echo $obj2 -> protected ; //Cannot access protected property echo $obj2 -> private ; //Cannot access priavte property $obj2 -> Display(); //Displays all properties ?>

输出如下：