扩展了PHP

Question

<?php 
class LoveBase 
{ 
    protected static $_instance = NULL; 
    protected function __construct() {} 
    public static function app() 
    { 
     if(self::$_instance == NULL) { 
      self::$_instance = new self(); 
     } 
     return self::$_instance; 
    } 

    public function get() 
    { 
     return 'LoveBase'; 
    } 

} 

class Love extends LoveBase 
{ 
    public static function app() 
    { 
     if(self::$_instance == NULL) { 
      self::$_instance = new self(); 
     } 
     return self::$_instance; 
    } 
    public function get() 
    { 
     return 'Love'; 
    } 
} 

// Print "LoveLove" in this case(first case) 
echo Love::app()->get(); 
echo LoveBase::app()->get(); 

// Print "LoveBaseLoveBase" in this case(second case) 
// echo LoveBase::app()->get(); 
// echo Love::app()->get(); 

1. 一个单独的类为什么两种不同的方法出来同样的结果？

2. 比较这两种情况，该方法将在首先实例化类时运行。

（对不起，我不擅长英语，希望可以让SENCE）

Answer 1

// Print "LoveLove" in this case(first case) 

//Set self::$_instance to Love object id 
echo Love::app()->get(); 

//Static property $_instance is now already set, so LoveBase::app() won't create new self(), it will just return created and saved Love object 
echo LoveBase::app()->get(); 

// Print "LoveBaseLoveBase" in this case(second case) 

// Here is the same case, but static property $_instance filled with new self() in LoveBase class 
// echo LoveBase::app()->get(); 
// echo Love::app()->get(); 

Answer 2

你定义了两个静态函数，这两者使用相同的静态变量（$ _instance） - 静态基类的成员也可以通过子类访问（只要它不是私有的）。请记住，静态的东西（方法和变量）会被继承，但不会被克隆。

解决方案：使成员变量为私有，并为每个类创建一个。

class LoveBase 
{ 
    private static $_instance = NULL; 
    // ... 

class Love extends LoveBase 
{ 
    private static $_instance = NULL; 
    // ...