PHP object-oriented data hiding

What is data hiding?

Some people may find it hard to understand when they see this. In the previous article, when introducing classes, we said that the keyword used to define variables is public, but there is more than just this one, there are also public, private, protected, static and final. These keywords are used to limit class members, including Access permissions for variables and methods. Next, we will first explain the usage of the first three keywords.

Friendly reminder:

The use of keywords to limit member variables and member methods is the same. So here we only use member variables as an example to illustrate the different uses of these keywords. The same applies to member methods.

Next, let’s introduce these keywords in detail:

(1) public

Chinese translation is public. As the name suggests, it is public and does not require hidden data information. It can be called by other classes and objects anywhere in the program (inside the class, outside the class). Subclasses can inherit and use all public members of the parent class.

Before explaining this chapter, we used public declarations to define variables and methods, and all methods are also public by default, so calling variables and methods is very confusing. To solve this situation, we are going to talk about the second keyword private.

Because public was used before, we will not give examples here.

(2) private

Chinese translation is private, private. Variables and methods modified by private can only be called and modified inside the class where they are located, and cannot be accessed outside the class. Neither is possible in subclasses.

Private example display:

<?php
header("content-type:text/html;charset=utf-8");
class Preson{
   private $name = "雷克赛";
   public function setName($name){
       $this -> name = $name;
   }
   public function getName(){
       return $this ->name;
   }
}
class Preson1 extends Preson{
}
$preson = new Preson();
//正确的使用方式
echo &#39;我的名字叫&#39;;
$preson ->setName("布里茨");    //通过访问成员方法进行赋值
echo $preson -> getName();      //在通过访问成员方法进行访问
//错误的使用方式
echo &#39;我的名字叫&#39;;
echo Preson :: $name;

In the above example, modification and access to the private variable $name can only be achieved by calling member methods. If called directly, an error will occur.

(3) protected

Chinese translation means protected. The private keyword can completely hide the data. It cannot be called anywhere except in this class, nor in subclasses. But in some cases, some variables need to be callable in subclasses, but for other classes, they still need to be encapsulated. This time we will use our protected keyword.

Class members modified with protected can be called in this class and subclasses, but cannot be called elsewhere.

Protected example display:

<?php
header("content-type:text/html;charset=utf-8");
class Preson{
   protected $name = &#39;维克托&#39;;
}
class Preson1 extends Preson{
   public function showName(){
       echo &#39;只有真确的调用，我才会出现&#39;;
       echo &#39;<br/>&#39;;
       echo &#39;我的名字是:&#39; . $this ->name;
       echo &#39;<br/>&#39;;
   }
}
$preson = new Preson1();
$preson -> showName();
echo &#39;你调用错了，所以下面不报错算我输：&#39;;
$preson -> name = &#39;德莱文&#39;;

In the above example, first declare a variable with the keyword protected, then call it once in the method of the subclass, and finally call it directly outside the class. The result It's clear at a glance.

Tips:

Although there are no mandatory regulations and requirements for keywords that modify variables in PHP, considering the characteristics and design of the object, Generally, the private and protected keywords are used to modify variables to prevent variables from being directly modified and called outside the class.

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