PHP面向对象

最新推荐文章于 2024-04-12 00:45:00 发布

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本文详细对比了PHP类中构造函数和析构函数的使用方式，与C++、Java的相似之处及区别。同时，介绍了PHP对象的内存管理机制，包括引用计数原理和析构函数的自动调用。通过示例代码，深入浅出地解释了这些概念。

PHP对象是与java,c++几点异同，

1.PHP 类可以复写构造函数__construct和析构函数,这一点与c++相似，如果不写则默认为无参构造和析构函数

<?php
class NBAPlayer {
}
$jordan = new NBAPlayer();

复写构造和析构函数

<?php
class NBAPlayer {
	public $name;
	public $height;
	public $weight;
	public $team;
	public $teamNumber;

	function __construct($name,$height,$weight,$team,$teamNumber){
		$this->name = $name;
		$this->height = $height;
		$this->weight = $weight;
		$this->team = $team;
		$this->teamNumber = $teamNumber;
		echo "construc a instance:".$name."<br/>";
	}
	function __destruct(){
		echo "Destroy a instance:".$this->name."<br/>";
	}
}
$jordan = new NBAPlayer("jordan","198cm","98kg","bull","23");
$james = new NBAPlayer("james","205cm","120kg","heat","10");

2. $jordan 是一个对象的引用，并且php对象的内存释放采用引用计数（与java类似)，为0时候由gc自动调用析构。

&创建一个影子（别名）引用，并不增加引用计数。

<?php
class NBAPlayer {
	public $name;
	public $height;
	public $weight;
	public $team;
	public $teamNumber;

	function __construct($name,$height,$weight,$team,$teamNumber){
		$this->name = $name;
		$this->height = $height;
		$this->weight = $weight;
		$this->team = $team;
		$this->teamNumber = $teamNumber;
		echo "construc a instance:".$name."<br/>";
	}
	function __destruct(){
		echo "Destroy a instance:".$this->name."<br/>";
	}
}
$jordan = new NBAPlayer("jordan","198cm","98kg","bull","23");
$james = new NBAPlayer("james","205cm","120kg","heat","10");
$james1 = $james;//相当于为james对象创建了一个新的引用
$james2 = &$james1;//创建一个影子引用，其实是一个别名
$james = null;
echo "james1 has not yet set to be nulled <br/>";
$james1 = null;//james对象调用析构(其引用计数已经为0)
echo "james1 has set to be nulled<br/>";

?>

运行结果：

construc a instance:jordan
construc a instance:james
james1 has not yet set to be nulled 
Destroy a instance:james
james1 has set to be nulled 
Destroy a instance:jordan