How to use $this, static, final, const, self and other keywords in php_PHP tutorial

This article mainly breaks down how to use the keywords $this, static, final, const, and self in the PHP class.

$this

$this represents the current instance. When the internal method of the class accesses attributes that are not declared as const and static, the form $this->value='phpernote'; is used. Common usages include:

$this->Property

$this->Method

For example:

<?php
class MyClass{
	private $name;
	public  function __construct($name){
		$this->name=$name;
	}
	public function getname(){
		return $this->name;
	}
	public  function printName(){
		echo $this->getname();
	}
}
$myclass= new MyClass("I Like PHP");
$myclass->printName();//输出：I Like PHP
?>

There are three ways to call the properties and methods of the current class in a class, namely self, parent, and $this. The difference between these three keywords is: self is used to point to the current class; parent is used to point to the current class. Parent class, you can use this keyword to call the properties and methods of the parent class; $this is used to call its own properties and methods within the class body.

static

The keyword can be self (used when calling static members inside a class) the class name of the static member (used when calling static members inside the class outside the class)

Declare a static variable as follows:

static $val='';

A variable that only exists in the function scope. The value of the variable will not be lost after the function is executed. It will only be initialized once. Expressions cannot be used to initialize static variables. Global variables are not used instead because global variables will be accessed by all functions and can easily cause problems. Not suitable for maintenance.

There are two main uses for using static in a class, defining static members and defining static methods. Static members only retain the value of one variable, which is valid for all instances, as follows:

<?php
class MyObject{
	public static $myStaticVar=0;
	function myMethod(){
		self::$myStaticVar+=2;
		echo self::$myStaticVar;
	}
}
$instance1=new MyObject();
$instance1->myMethod();
$instance2=new MyObject();
$instance2->myMethod();
//结果将分别打印2、4

<?php
class Book{
	static $num=0;
	public function showMe(){
		echo"您是滴".self::$num."位访客";
		self::$num++;
	}
}
$book1=new Book();
$book1->showMe();
echo"<br>";
$book2=new Book();
$book2->showMe();
echo"<br>";
echo"您是滴".Book::$num."位访客";
?>

The result will be:

You are 0 visitors
You are a visitor
You are 2 visitors

Another thing to note is that if a class method is static, the properties it accesses must also be static.

final

The final class and method cannot be inherited, and the method modified by this keyword cannot be overridden. General usage is as follows:

<?php
final class MyClass{//此类将不允许被继承
	final function fun1(){......}//此方法将不允许被重写
}

const

When the internal method of a class accesses attributes that have been declared as const and static, it needs to be called in the form of self::$name. Examples are as follows:

<?php
class clss_a{
	private static $name="static class_a"; 
	const PI=3.14; 
	public $value; 
	public static function getName(){ 
		return self::$name; 
	} 
	//这种写法有误，静态方法不能访问非静态属性 
	public static function getName2(){ 
		return self::$value; 
	} 
	public function getPI(){ 
		return self::PI; 
	}
}

Note that the declaration format of const attributes is const PI=3.14, not const $PI=3.14.

self

self represents the class itself, pointing to the current class. Usually used to access static members, methods and constants of a class.

Articles you may be interested in

• The difference between variables and functions in PHP after adding the static keyword before them
• Return and exit in PHP, The difference and usage of break and contiue
• php prompt PHP Warning: date(): It is not safe to rely on the... Error solution
• php prompt Maximum execution time of 30 seconds exceeded... Solution to the error
• Usage and difference between using break, continue, goto, return, exit to break out of multiple loops in PHP
• window.navigate and window.location. Detailed explanation of the usage difference of href
• Usage and difference of echo, print, print_r, var_export, var_dump in php
• php prompt Call to undefined function curl_init() error solution

http://www.bkjia.com/PHPjc/764117.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/764117.htmlTechArticleThis article mainly breaks down the $this, static, final, const, self in the PHP class Several keyword usage methods. $this $this represents the current instance, which is not accessed by the internal method of the class...