是否可以在PHP中创建静态类(如在C#中)？

Question

我想在PHP中创建一个静态类,并使其行为与在C#中的行为相同,所以

1. 第一次调用类时会自动调用构造函数
2. 无需实例化

这种东西......

static class Hello {
    private static $greeting = 'Hello';

    private __construct() {
        $greeting .= ' There!';
    }

    public static greet(){
        echo $greeting;
    }
}

Hello::greet(); // Hello There!

Answer 1

您可以在PHP中使用静态类,但它们不会自动调用构造函数(如果您尝试调用self::__construct(),则会收到错误).

因此,您必须创建一个initialize()函数并在每个方法中调用它:

<?php

class Hello
{
    private static $greeting = 'Hello';
    private static $initialized = false;

    private static function initialize()
    {
        if (self::$initialized)
            return;

        self::$greeting .= ' There!';
        self::$initialized = true;
    }

    public static function greet()
    {
        self::initialize();
        echo self::$greeting;
    }
}

Hello::greet(); // Hello There!


?>

Answer 2

除了Greg的回答之外,我还建议将构造函数设置为private,以便无法实例化该类.

所以在我的拙见中,这是一个基于Greg的更完整的例子:

<?php

class Hello
{
    /**
     * Construct won't be called inside this class and is uncallable from
     * the outside. This prevents instantiating this class.
     * This is by purpose, because we want a static class.
     */
    private function __construct() {}
    private static $greeting = 'Hello';
    private static $initialized = false;

    private static function initialize()
    {
        if (self::$initialized)
            return;

        self::$greeting .= ' There!';
        self::$initialized = true;
    }

    public static function greet()
    {
        self::initialize();
        echo self::$greeting;
    }
}

Hello::greet(); // Hello There!


?>

Answer 3

你可以拥有那些"静态"类.但我想,缺少一些非常重要的东西:在php中你没有应用程序循环,所以你不会在整个应用程序中获得真正的静态(或单例)...

请参阅PHP中的Singleton

Answer 4

final Class B{

    static $staticVar;
    static function getA(){
        self::$staticVar = New A;
    }
}

b 的结构称为单例处理程序，您也可以在 a 中执行此操作

Class a{
    static $instance;
    static function getA(...){
        if(!isset(self::$staticVar)){
            self::$staticVar = New A(...);
        }
        return self::$staticVar;
    }
}

这是单例使用 $a = a::getA(...);