Basic knowledge analysis of PHP object-oriented programming

Basic knowledge analysis of PHP object-oriented programming

Introduction:
Object-oriented programming (Object Oriented Programming, referred to as OOP) is a methodology for program development. It abstracts things in the real world into objects, and completes program functions through interaction and information sharing between objects. PHP is a powerful programming language that is widely used in web development. Using an object-oriented approach in PHP can improve the maintainability and reusability of the code. This article will introduce the basics of object-oriented programming in PHP and illustrate it with code examples.

1. Classes and Objects
In object-oriented programming, a class is the template of an object, describing the properties and methods that the object should have. An object is an instance of a class and can be created using the new operator. The following is a simple sample code for classes and objects:

class Car {
    public $brand;
    public $color;
    
    public function startEngine() {
        echo "启动引擎。";
    }
    
    public function honk() {
        echo "按喇叭。";
    }
}

$myCar = new Car();
$myCar->brand = "BMW";
$myCar->color = "红色";

$myCar->startEngine();  // 输出：启动引擎。
$myCar->honk();         // 输出：按喇叭。

In the above code, we define a class named Car, which has two properties: brand and color, as well as startEngine() and honk( ) two methods. By using the new operator, an instance object $myCar of the Car class is created and its properties are assigned values. Finally, the corresponding function output can be achieved by calling the object's method.

2. Constructor and destructor methods
The constructor (Constructor) is a method that is automatically called when creating an object. Its function is to initialize the object. In PHP, the name of the constructor method is always __construct(), and you can define the parameters of the method as needed.

The destructor method (Destructor) is a method that is automatically called when the object is destroyed. Its role is to perform necessary resource release operations. The name of the destructor method is always __destruct().

The following is a sample code containing a constructor and a destructor:

class Dog {
    public $name;
    
    public function __construct($name) {
        echo "创建了一只名叫" . $name . "的狗。";
        $this->name = $name;
    }
    
    public function __destruct() {
        echo "销毁了" . $this->name . "。";
    }
}

$myDog = new Dog("旺财");  // 输出：创建了一只名叫旺财的狗。
unset($myDog);            // 输出：销毁了旺财。

In the above code, we define a Dog class and output a sentence to create an object in the constructor. Prompt information. After creating the object, we use the unset() function to destroy the object, which will automatically call the destructor method and output a prompt message for destroying the object.

3. Access control
Through access control, we can encapsulate the attributes and methods of the class to achieve data hiding and protection. The keywords used to implement access control in PHP are public, protected and private.

• Public properties and methods can be accessed by anyone without access restrictions.
• Protected properties and methods can only be accessed within the class and subclasses.
• Private properties and methods can only be accessed within the class.

The following is a sample code:

class Person {
    public $name;             // 公有属性
    protected $age;           // 受保护的属性
    private $gender;          // 私有属性
    
    public function __construct($name, $age, $gender) {
        $this->name = $name;
        $this->age = $age;
        $this->gender = $gender;
    }
    
    public function getInfo() {
        echo "姓名：" . $this->name . "，年龄：" . $this->age . "，性别：" . $this->gender;
    }
}

$person = new Person("张三", 25, "男");
echo $person->name;             // 输出：张三
echo $person->age;              // 报错，无法访问受保护的属性
echo $person->gender;           // 报错，无法访问私有属性
$person->getInfo();             // 输出：姓名：张三，年龄：25，性别：男

In the above code, we define a Person class, where name is a public attribute and can be accessed directly; age is a protected attribute, which can only It can be accessed within the class and subclasses; gender is a private attribute and can only be accessed within the class. After creating the object, we can directly access the name attribute, but cannot access the age and gender attributes. We can then access the values ​​of protected and private properties indirectly by calling the getInfo() method.

Conclusion:
This article introduces the basic knowledge of PHP object-oriented programming, including the concepts of classes and objects, the use of constructors and destructors, and access control related content. By learning and understanding these basic knowledge, we can better use the object-oriented approach to develop PHP programs and improve the maintainability and reusability of the code. In practical applications, we can also learn more advanced object-oriented programming techniques, such as inheritance, polymorphism, interfaces, etc., to further improve our programs.

Reference materials:

• PHP official documentation: http://php.net/
• W3School PHP tutorial: https://www.w3schools.com/ php/

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