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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, then it can be accessed from anywhere.
2. If a class member is declared protected, it can only be accessed within the class itself and in inheritance and parent classes.
3. If a class member is declared private, it can only be accessed by the class that defines the member.
public: This modifier can be used both internally and externally.
Example:
<?php class pub { public $tag_line = "PHP中文网!"; function display() { echo $this->tag_line."<br/>"; } } class child extends pub { function show(){ echo $this->tag_line; } } $obj= new child; echo $obj->tag_line."<br/>"; $obj->display(); $obj->show();
Output:
PHP中文网! PHP中文网! PHP中文网!
protected: This modifier can be used in the class in which it is defined and its parent or inherited class .
Example:
<?php class pro { protected $x = 500; protected $y = 500; function sub() { echo $sum=$this->x-$this->y . "<br/>"; } } class child extends pro { function mul() { echo $sub=$this->x*$this->y; } } $obj= new child; $obj->sub(); $obj->mul(); ?>
Output:
0 250000
private: This modifier can be used in the class in which it is defined. (It cannot be accessed outside the class means inherited class).
Example:
<?php class demo { private $name="PHP中文网"; private function show() { echo "这是基(父)类的私有方法"; } } class child extends demo { function display() { echo $this->name; } } $obj= new child; $obj->show(); $obj->display();
Output: The error shown in the figure is because private class data cannot be accessed outside the class.
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