Understanding of PHP class objects attributes and methods

1. Create classes and objects

User-defined classes are also one of the necessary conditions for learning PHP well. Compared with classes in other object-oriented languages, classes in PHP are relatively simple. PHP only has classes, methods, attributes, single inheritance (extensions), etc. In PHP, it is very simple to create a class. You only need the keyword class. The definition of the simplest class is as follows:

class class_name
{
//用关键字var定义类的属性，属性的类型支持PHP的所有数据类型，也可以是一个对象
var $var_1;
var $var_2;
…
var $var_n;
//用关键字function定义类的方法
function method_1(…){…}
function method_2(…){…}
…
function method_n(…){…}
}

Among them, class is the keyword that must be used to declare the class; class_name represents the class The choice of name and class name should have a certain meaning, so as to facilitate memory and understanding; {} is used to identify the beginning and end of the class.

Note: If you use the class's own attributes or methods in the internal implementation of the class, you need to add "$this" before the "->" attribute or method to indicate that you are using its own members, and At this time, the "$" mark is no longer used before the attribute.

Use the keyword new in PHP to create an object of a class. The syntax is as follows:

$object_name=new class_name

Among them, object_name is the object to be created. The name, the keyword new is used to create an object, and class_name is the class name.

2. Use classes to encapsulate code to make it more convenient to call, have higher code integration, better scalability, and stronger maintainability. This example mainly applies to classes, including class declaration, class body and calling class. Write a book information class and use PHP to call the class. When writing a class, the class should be written in a PHP page, so that the definition and methods of the class are located in a PHP page. When the class is modified, there is no need to recompile, and only the PHP page code needs to be re-run.

(1) Write a book class in the class_book.php file.

Use class to indicate that it is a class category. The book in the function in the class represents a method of the class. Methods can encapsulate the actual processing situation of a class, allowing the class to independently perform some steps according to the encapsulated method.

<?php
class book{          //声明类
var $book_ID;       //图书编号
var $book_name;     //图书名称
var $book_author;    //作者
var $book_TPI;      //出版社
var $book_price;     //定价
function book($ID,$Name,$Author,$TPI,$Price){
$this->book_ID=$ID;
$this->book_name=$Name;
$this->book_author=$Author;
$this->book_TPI=$TPI;
$this->book_price=$Price;
}
}
?>

The $this class variable in the program is a special variable in PHP. The $this variable is only used in the class category to represent the class itself.

(2) Call class method. Save the above defined class as a php file, and then use require (or include) to include it. When defining the variable $obj, use the reserved word of new and use the "->" symbol to indicate the method of executing the class.

<?php include "class_book.php" ?>
<?php
$obj=new book("7-115-14688-8", "php 数据库开发实例教程", "周五", "长江出版社", 49);
echo "图书编号：$obj->book_ID<br>";
echo "图书名称：$obj->book_name<br>";
echo "作　　者：$obj->book_author<br>";
echo "出 版 社：$obj->book_TPI<br>";
echo "定　　价：$obj->book_price<br>";
?>

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