PHP实现一个限制实例化次数的类示例

本文实例讲述了php实现一个限制实例化次数的类。分享给大家供大家参考，具体如下：

实现思路

1. 定义一个static变量$count，用于保存实例化对象的个数
2. 定义一个static方法create，通过该方法判断$count的值，进而判断是否进一步实例化对象。
3. 定义构造函数，$count+1
4. 定义析构函数，$count-1

实现代码

<?php
class demo{
  public $name;
  public static $count=0;
  private function __construct($name){
    echo "create $name <br/>";
    $this->name = $name;
    self::$count++;
  }
  public function __destruct(){
    echo "destory ".$this->name."<br/>";
    self::$count--;
  }
  public static function create($name){
    if(self::$count>2){
      die("you can only create at most 2 objects.");
    }else{
      return new self($name);
    }
  }
}
$one = demo::create("one");
$two = demo::create("two");
$two = null;
$three = demo::create("three");

运行结果：

create one
create two
destory two
create three
destory three
destory one