Examples of using static methods in PHP classes_PHP tutorial-PHP Tutorial-php.cn

For static methods in php, we just add static before the function or variable. When used, it is similar to static variables. There is no need to instantiate. It can be called directly with::. Let me give you some examples. An example of a static method.

PHP is no exception! The so-called static methods (properties) are properties or methods marked with the static keyword (for example: static properties public static username;)
The biggest difference between static methods and non-static methods is their different life cycles. Let’s use an example to illustrate

Static method definition

It is very simple to define a static method. Add static before declaring the keyword function, for example:

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代码如下	复制代码
class A { static function fun() { // do somathing } }

class A

{

static function fun()

{

// do somathing

代码如下	复制代码
A::fun()

}

Static method usage

代码如下

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class MyClass
{
public $num = 5;

    function __construct()
    {
        $this->num = 10;
    }

    function fun_1()
    {
        echo "I am a public method named fun_1.n";
        echo "The num of object is {$this->num}.n";
    }

    static function fun_2()
    {
        echo "I am a static method named fun_2.n";
    }

    function fun_3($n)
    {
        echo "The arg is {$n}n";
    }
}

$m = new MyClass;
$m->fun_1();
$m->fun_2();
$m->fun_3('test');

MyClass::fun_1();
MyClass::fun_2();
MyClass::fun_3('test');

输出结果：

lch@localhost:php $ php class_method.php
I am a public method named fun_1.
The num of object is 10.
I am a static method named fun_2.
The arg is test
I am a public method named fun_1.
PHP Fatal error: Using $this when not in object context in /Users/lch/program/php/class_method.php on line 14

is similar to a static variable when used. It does not need to be instantiated. It can be called directly with::, for example:

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A::fun()

Compared with ordinary methods Because calling static methods does not require instantiation, an error will occur when referencing the properties or methods of the class itself in a static method, that is, the forms self and $this are wrong.

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class MyClass { Public $num = 5; function __construct() { $this->num = 10; } function fun_1() { echo "I am a public method named fun_1.n"; echo "The num of object is {$this->num}.n"; } static function fun_2() { echo "I am a static method named fun_2.n"; } function fun_3($n) { echo "The arg is {$n}n"; } } $m = new MyClass; $m->fun_1(); $m->fun_2(); $m->fun_3('test'); MyClass::fun_1(); MyClass::fun_2(); MyClass::fun_3('test'); Output result: lch@localhost:php $ php class_method.php I am a public method named fun_1. The num of object is 10. I am a static method named fun_2. The arg is test I am a public method named fun_1. PHP Fatal error: Using $this when not in object context in /Users/lch/program/php/class_method.php on line 14

Look at another example

Use an example to illustrate.

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代码如下

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class user{
public static $username; //声明一个静态属性
public $password; //声明一个非静态属性

function __construct($pwd) {
echo ‘Username:’,self::$username; //输出静态属性

self::$username = ‘admin’; //为静态属性赋值
$this->password = $pwd; //为非静态属性赋值
}

public function show(){ //输出类属性
echo ‘
Username:’,self::$username;
echo ‘
Password:’,$this->password;
}

public static function sshow(){
echo ‘
Username:’,self::$username;
echo ‘
Password:’,$this->password;
}
}
user::$username = ‘root’; //为赋值user类的静态属性赋值
$objUser = new user(’123456′); //实例化user类
$objUser->sshow();
unset($objUser);
echo ‘
Username:’,user::$username;

/*
* 输出结果为：
* Username:root
* Username:admin
* Password:123456
* Usern
ame:admin
* */

class user{

public static $username; //Declare a static property
public $password; //Declare a non-static property

function __construct($pwd) {

echo ‘Username:’,self::$username; //Output static attributes

self::$username = ‘admin’; //Assign values to static attributes

$this->password = $pwd; //Assign values to non-static properties

}

代码如下

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class Log
{
    public $root = DIRECTORY_SEPARATOR;
    public $logPath = '/data/app/www/test-realtime.monitoring.c.kunlun.com/log';
    public $defaultDir = 'default';

    public function writeLog($logName, $logType, $data, $newDir = FALSE)
    {
        $fileName = '';

        if (!file_exists($this->logPath))
        {
            mkdir($this->logPath, 0777);
        }

        if ($newDir !== FALSE)
        {
            @mkdir($this->logPath.$this->root.$newDir, 0777);
            $fileName = $this->logPath.$this->root.$newDir.$this->root.date('Y-m-d', time()).'_'.$logName.'_'.$logType.'.log';
        }
        else
        {
            @mkdir($this->logPath.$this->root.$this->defaultDir, 0777);
            $fileName = $this->logPath.$this->root.$this->defaultDir.$this->root.date('Y-m-d', time()).'_'.$logName.'_'.$logType.'.log';
        }

        file_put_contents($fileName, date('Y-m-d H:i:s').' '.$data."n", FILE_APPEND);
    }
}

public function show(){ //Output class attributes echo ‘ Username:’,self::$username; echo ‘ Password:’,$this->password; } public static function sshow(){ echo ‘ Username:’,self::$username; echo ‘ Password:’,$this->password; } } user::$username = ‘root’; //Assign a value to the static attribute of the user class $objUser = new user(’123456′); //Instantiate user class $objUser->sshow(); unset($objUser); echo ‘ Username:’,user::$username; /* * The output result is: * Username:root * Username:admin * Password:123456 *Usern ame:admin * */

As can be seen from this example, static properties work before the class is instantiated, and static properties can still play a role when the object is destroyed! Also because of this property of static methods, non-static properties or methods cannot be called in static methods Read on 1. In the PHP class, assuming that the visibility of all properties and methods is public, then when accessing the methods or properties of the class externally, they must be called through the object [instantiation process of the class]. eg:

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class Log { Public $root = DIRECTORY_SEPARATOR; Public $logPath = '/data/app/www/test-realtime.monitoring.c.kunlun.com/log'; Public $defaultDir = 'default'; Public function writeLog($logName, $logType, $data, $newDir = FALSE) { $fileName = ''; If (!file_exists($this->logPath)) { mkdir($this->logPath, 0777); } If ($newDir !== FALSE) { @mkdir($this->logPath.$this->root.$newDir, 0777); $fileName = $this->logPath.$this->root.$newDir.$this->root.date('Y-m-d', time()).'_'.$logName.'_' .$logType.'.log'; } else { @mkdir($this->logPath.$this->root.$this->defaultDir, 0777); $fileName = $this->logPath.$this->root.$this->defaultDir.$this->root.date('Y-m-d', time()).'_'.$logName .'_'.$logType.'.log'; } file_put_contents($fileName, date('Y-m-d H:i:s').' '.$data."n", FILE_APPEND); } }

The process of instantiating objects of a class: $logObj = new Log();

Access methods in the class: $logObj->writeLog($param1, $param2, $param3, $param4);

Access properties in the class: echo $logObj->root;

2. If the attributes in the class are previously modified by the static keyword, you cannot access the attributes modified by static through the object. However, if the method in the class is modified by static, you can access it through the object or the class. Name:: method name to access.

3. If the method in the class is modified by static, $this cannot be used in the method. $this refers to the instantiation object of the class. Since static methods can be called without passing the object, the pseudo variable $this is not available. .