Detailed explanation of PHP object-oriented programming: classes and objects

From an OOP perspective, languages should not be distinguished. Whether it's C, Java, .net or more object-oriented languages, as long as you understand the true meaning of OO, you can transcend languages and let your thoughts jump easily. There is no longer a dispute about who is stronger among Java, .net, and PHP.

I hope this introduction to PHP5 object-oriented programming (OOP) will benefit beginners and enable more PHPers to start switching to the OO programming process.

Compared with PHP4, PHP5 has changed a lot in terms of object orientation. We will only introduce object-oriented in PHP5 environment. And we must change ourselves to follow the development of PHP5. If the code results are inconsistent in your environment, please confirm that your environment is PHP5.

We assume that the reader does not have any object-oriented knowledge. Even if you are hearing about OOP for the first time, you can still understand this article. But I hope you must have some knowledge about PHP.

We will use some examples later to gradually analyze the OO foundation of PHP5.

Object-oriented only solves two problems, code scalability and code maintainability.

I have to say that php is becoming more and more like Java.

Compilation reference: http://www.lai18.com/content/425094.html

Everything is Object: Everything is an object.

The idea of object-oriented programming (OOP) strives to make the description of things in computer language as consistent as possible with the true appearance of the things in the real world. Object-oriented language is closely related to our lives, and it is actually very simple to learn object-oriented language. The application is more in line with our life logic.

Class is used to describe an object:

Classes describe the data that each object should contain, and classes describe the behavioral characteristics of each object.

Class/Object: Class and object are the core concepts of the object-oriented method.

Class is a description of a type of thing, an abstract and conceptual definition;

An object is every individual of this type of thing that actually exists, so it is also called an instance. In a computer, it can be understood that a real memory area is created in the memory to store this object.

The process of creating an object is called object creation, also known as instantiation.

Classes and objects in PHP5

Let's create a basic class first.

The keyword class is used in PHP to define a class. Class names generally use the first character to be capitalized, and then the first character of each word is capitalized to facilitate reading.

<!--?
class Person 
{
 
}
$p = new Person();
echo $p;
?-->

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With this, we have our first PHP class.

Let’s continue to use this class, use the new keyword to create objects, and use echo to print $p

We defined a variable $p and created a Person object using the new keyword.

Printing the variable $p, we see the output Object id #1, indicating that this is an object.

$p = new Person(); can also be written as $p = new Person;, but the latter method is not recommended.

Properties in PHP5

Attributes: The data elements used to describe an object are called attributes (also called data/state) of the object

In PHP5, attributes refer to variables declared in a class. When declaring a variable, it must be modified with one of public private protected to define the access rights of the variable.

Public: Can be freely read and modified inside and outside the class.

Private: Can only be read and modified within the current class.

Protected: Can be read and modified in this class and its subclasses.

Usage of attributes: Call the attribute of the object pointed to by the variable through the -> symbol that refers to the variable.

A property of the same object is called via the $this-> notation inside a method.

<!--?
class Person{
   public $name = "Gonn"; //定义public属性 $name.
   public $age = 20; // 定义 public 属性 $age;
}
$p = new Person(); // 创建对象
echo $p."<br-->";    // 输出对象
echo "他的名字是 ".$p->name;     // 输出对象$p的属性 $name;
echo "
";
echo &#39;他的年龄是 &#39;$p->age; //输出age属性.
?>

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The program output is:

他的名字是 Gonn
他的年龄是 24

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The Person class has two attributes, $name and $age. After instantiation, use $p->name and $p->age to print out the contents of the attributes.

Of course, you can not set the initial value when defining the attribute, in which case no results will be printed.

Change the properties of the object, pay attention to lines 8 and 9 of code, and the changes in the output results. We see that the output attribute value has been changed.

<!--?
// 1-4.php
class Person{
   public $name = "NoName"; //定义public属性 $name.
   public $age = 20; // 定义 public 属性 $age;
}
$p = new Person(); // 创建对象
$p--->name = &#39;Tom&#39;; //变更姓名为 Tom
$p->age = 25 ; // 变更年龄为 25 岁.
echo "他的名字是 ".$p->name;     // 输出对象$p的属性 $name;
echo "
";
echo &#39;他的年龄是 &#39;.$p->age; //输出age属性.
?>

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Create a Person object and change the properties of this object. Name it and see its name. You are the god of the Person object in the machine. According to the rules you defined, this real Person object in memory is created, and it has properties that can be changed.

Now, we are the gods of the computer world, ready to create the world.

Properties modified by Private cannot be accessed outside the current object. Private attributes are set to hide data.

隐藏：指对象的一种保护机制，使得它的属性或方法不被外部的程序直接访问。

<!--?
// 1-3.php
class Person{
   private $name = "Gonn"; //定义public属性 $name.
   public $age = 20; // 定义 public 属性 $age;
}
$p = new Person(); // 创建对象
echo "他的名字是 ".$p--->name;     // 输出对象$p的属性 $name;
?>

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运行此程序将会输出：

Fatal error: Cannot access private property Person::$name in E:\PHPProjects\test.php on line 9

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私有属性不能被外部访，这样做的好处后面会介绍到。

延伸阅读

此文章所在专题列表如下：

PHP面向对象编程详解：类和对象
PHP面向对象编程详解：类的属性
PHP面向对象编程详解：类的方法
PHP面向对象编程详解：对象的比较
PHP面向对象编程详解：构造函数
PHP面向对象编程详解：类的继承
PHP面向对象编程详解：访问控制
PHP面向对象编程详解：方法覆盖
PHP面向对象编程详解：this关键字
PHP面向对象编程详解：parent::关键字
PHP面向对象编程详解：再谈重载
PHP面向对象编程详解：获取用户数据
PHP面向对象编程详解：用户权限管理类
PHP面向对象编程详解：static变量与方法
PHP面向对象编程详解：单例模式
PHP面向对象编程详解：final类和方法
PHP面向对象编程详解：PHP中的常量
PHP面向对象编程详解：抽象类
PHP面向对象编程详解：抽象方法
PHP面向对象编程详解：抽象类继承抽象类
PHP面向对象编程详解：静态抽象方法
PHP面向对象编程详解：模板模式
PHP面向对象编程详解：接口与抽象方法
PHP面向对象编程详解：接口的实现
PHP面向对象编程详解：接口的继承
PHP面向对象编程详解：类型提示
PHP面向对象编程详解：PHP的多态
PHP面向对象编程详解：instanceof运算符
PHP面向对象编程详解：接口与组合模拟多继承
PHP面向对象编程详解：一个接口实例
PHP面向对象编程详解：简单工厂模式