Object-oriented design principles PHP object-oriented guide (17) Automatic loading of classes

Automatically load classes
When many developers write object-oriented applications, they create a PHP source file for each class definition. A big
annoyance is having to write a long list of include files at the beginning of each script (one file per class).
In a software development system, it is impossible to write all classes in a PHP file. When a PHP file
needs to call a class declared in another file, this file needs to be introduced through include. But sometimes,
In projects with many files, it is a headache to include all the files of the required classes one by one, so
Can we include the classes when they are used? What about the import of the PHP file where this class is located? This is the autoloading class we are going to talk about here.
In PHP5, you can define an __autoload() function, which will be automatically called when trying to use a class that has not yet been defined. By calling this function, the script engine has the last chance to load the required content before PHP fails with an error. class, one parameter received by the
__autoload() function is the class name of the class you want to load, so when you are working on a project, you need to follow certain rules when organizing and defining the file name of the
class. It is best to use the class name As the center, you can also add a unified prefix or suffix to form a file name, such as xxx_classname.php, classname_xxx.php and classname.php, etc.
This example attempts to load the MyClass1 and MyClass2 classes from the MyClass1.php and MyClass2.php files respectively
Code snippet



Copy the code

The code is as follows:function __autoload($classname) {

require_once $classname . '.php';
}
//The MyClass1 class does not automatically call the __autoload() function, pass in the parameter "MyClass1"
$obj = new MyClass1();
//The MyClass2 class does not exist and automatically calls __autoload() function, pass in the parameter "MyClass2"
$obj2 = new MyClass2();
?>


The above introduces the object-oriented design principles PHP object-oriented guide (17) Automatically loading classes, including the object-oriented design principles, I hope it will be helpful to friends who are interested in PHP tutorials.