Detailed interpretation of PHP class encapsulation

Detailed interpretation of PHP class encapsulation_PHP tutorial

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Release： 2016-07-15 13:33:21

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public: The method or property can be accessed in any scope, and this is the default. If no access modifier is specified for a property or method, It will be public.

protected: The method or property can only be accessed from a member of the class or inherited class.

private: The method or property can only be accessed from a member of the class, and cannot be accessed from members of the inherited class. Methods or properties marked private can be redefined in inherited classes. Each class can only see its own private methods.

These three modifiers should be sorted from large to small in terms of scope like this:

public→protected→private. The reason why it is said to be in scope is because the class is the same as before us. Like the functions, some attributes and methods are encapsulated in PHP classes. This encapsulation determines the "visibility" of the data, so that we cannot modify the defined properties and methods at will outside the class but can only call them. This is the benefit of encapsulation, and it also improves security. To illustrate the role of these modifiers, please look at the following code:

<ol class="dp-xml">
<li class="alt"><span><span class="tag"><</span><span> ?php   </span></span></li><li><span>class myClass{   </span></li><li class="alt"><span>public $</span><span class="attribute">public</span><span>=</span><span class="attribute-value">"Public"</span><span>;   </span></li><li><span>protected $</span><span class="attribute">protected</span><span>=</span><span class="attribute-value">"Protected"</span><span>;   </span></li><li class="alt"><span>private $</span><span class="attribute">private</span><span>=</span><span class="attribute-value">"Private"</span><span>;   </span></li><li><span>function say_Hello(){   </span></li><li class="alt"><span>//我现在什么也不做，等下再告诉你   </span></li><li><span>}   </span></li><li class="alt"><span>}   </span></li><li><span>$</span><span class="attribute">obj</span><span>=</span><span class="attribute-value">new</span><span> myClass();   </span></li><li class="alt"><span>echo $obj-</span><span class="tag">></span><span>public;   </span></span></li>
<li>
<span>//echo $obj-</span><span class="tag">></span><span>protected;   </span>
</li>
<li class="alt">
<span>//echo $obj-</span><span class="tag">></span><span>private;   </span>
</li>
<li>
<span class="tag">?></span><span>   </span>
</li>
<li class="alt">
<span class="tag"><</span><span> ?php  </span></li><li><span>class myClass{  </span></li><li class="alt"><span>public $</span><span class="attribute">public</span><span>=</span><span class="attribute-value">"Public"</span><span>;  </span></li><li><span>protected $</span><span class="attribute">protected</span><span>=</span><span class="attribute-value">"Protected"</span><span>;  </span></li><li class="alt"><span>private $</span><span class="attribute">private</span><span>=</span><span class="attribute-value">"Private"</span><span>;  </span></li><li><span>function say_Hello(){  </span></li><li class="alt"><span>//我现在什么也不做，等下再告诉你  </span></li><li><span>}  </span></li><li class="alt"><span>}  </span></li><li><span>$</span><span class="attribute">obj</span><span>=</span><span class="attribute-value">new</span><span> myClass();  </span></li><li class="alt"><span>echo $obj-</span><span class="tag">></span><span>public;  </span>
</li>
<li>
<span>//echo $obj-</span><span class="tag">></span><span>protected;  </span>
</li>
<li class="alt">
<span>//echo $obj-</span><span class="tag">></span><span>private;  </span>
</li>
<li>
<span class="tag">?></span><span>   </span>
</li>
</ol>

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By running the above example we get a "Public", but when you When you remove the comment of //echo $obj->private;, you will get the following error: Fatal error: Cannot access protected property myClass::$protected in E:apachehtdocsexamplefile.php on line 13.

You can see that we cannot access the attribute definitions of the class at will, that is, we cannot modify some operations that have been defined in the encapsulation of the PHP class. This is visibility. We don't know "outside" what members are in this class, because these members may not be visible to other classes.

Of course, if we must access or modify properties defined as "private", we can also use the system methods provided by PHP: _get() and _set(). I will learn more about this later, because now I only have an understanding of it.