php单例模式的实现_PHP教程

<?<span php

</span><span /*</span><span *
* 设计模式之单例模式
* $_instance必须声明为静态的私有变量
* 构造函数和析构函数必须声明为私有,防止外部程序new
* 类从而失去单例模式的意义
* getInstance()方法必须设置为公有的,必须调用此方法
* 以返回实例的一个引用
* ::操作符只能访问静态变量和静态函数
* new对象都会消耗内存
* 使用场景:最常用的地方是数据库连接。 
* 使用单例模式生成一个对象后，
* 该对象可以被其它众多对象所使用。 
</span><span */</span>
<span class</span><span  Example
{
</span><span //</span><span 保存例实例在此属性中</span>
<span private</span> <span static</span> <span $_instance</span><span ;

</span><span //</span><span 构造函数声明为private,防止直接创建对象</span>
<span private</span> <span function</span><span  __construct()
{
</span><span echo</span> 'I am Construceted'<span ;
}

</span><span //</span><span 单例方法</span>
<span public</span> <span static</span> <span function</span><span  singleton()
{
</span><span if</span>(!<span isset</span>(self::<span $_instance</span><span ))
{
</span><span $c</span>=<span __CLASS__</span><span ;
self</span>::<span $_instance</span>=<span new</span> <span $c</span><span ;
}
</span><span return</span> self::<span $_instance</span><span ;
} 

</span><span //</span><span 阻止用户复制对象实例</span>
<span public</span> <span function</span><span  __clone()
{
</span><span trigger_error</span>('Clone is not allow' ,<span E_USER_ERROR</span><span );
}

</span><span function</span><span  test()
{
</span><span echo</span>("test"<span );

}
}

</span><span //</span><span  这个写法会出错，因为构造方法被声明为private</span>
<span $test</span> = <span new</span><span  Example;

</span><span //</span><span  下面将得到Example类的单例对象</span>
<span $test</span> = Example::<span singleton();
</span><span $test</span>-><span test();

</span><span //</span><span  复制对象将导致一个E_USER_ERROR.</span>
<span $test_clone</span> = <span clone</span> <span $test</span><span ;
</span>?>