Single instance and multiple instance design patterns of PHP design patterns

Single instance and multiple instance design patterns of PHP design patterns_PHP tutorial

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Release： 2016-07-20 11:14:19

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The Singleton pattern and the uncommon Multiton pattern control the number of classes in the application. As in the pattern name, the singleton can only be instantiated once and has only one object, while the multi-instance pattern can be instantiated multiple times.

Based on the characteristics of Singleton, we often use Singleton to configure applications and define variables that may be accessed at any time in the application. But sometimes it is not recommended to use Singleton because it generates a global state and

This single root object does not encapsulate any system functionality. In many cases, this makes unit testing and debugging difficult. Readers make their own decisions based on circumstances.

Code example:

<?<span php
</span><span class</span><span  SingletonExample{
    </span><span private</span> <span function</span> __construct(){}<span //</span><span 防止直接实例化</span>

  <span public</span> <span static</span> <span function</span> getInstance(){ <span //</span><span 不与任何对象有关联</span>
 <span static</span> <span $instance</span>=<span null</span>;    <span //</span><span 调用此函数的所有代码共享该变量，不必要让其是类的静态变量</span>
 <span if</span>(<span $instance</span>==<span null</span><span ){
   </span><span $instance</span>=<span new</span><span  SingletonExample();
     }
   </span><span return</span> <span $instance</span><span ;
  }
}
</span><span $obj1</span>=SingletonExample::<span getInstance();
</span><span $obj2</span>=SingletonExample::<span getInstance();
</span><span var_dump</span>(<span $obj1</span>===<span $obj2</span>);<span //</span><span  true   是同一个实例</span>
?>

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Multiton is similar to singleton, except that the latter requires the getInstance() function to pass the key value.

There will only be a unique object instance for a given key value. If there are multiple nodes, each node has a unique identifier, and each node may appear in a single execution (such as nodes in cms) Multiple times, then you can use Multiton mode to implement these nodes. Multiton saves memory and ensures that multiple instances of the same object do not conflict.

Example:

<span  1</span> <?<span php
</span><span  2</span> <span class</span><span  MultitonExample{
</span><span  3</span> <span private</span> <span function</span> __construct(){}<span //</span><span 防止直接实例化</span>
<span  4</span> 
<span  5</span>   <span public</span> <span static</span> <span function</span> getInstance(<span $key</span><span ){ 
</span><span  6</span>  <span static</span> <span $instance</span>=<span array</span><span ();    
</span><span  7</span>  <span if</span>(!<span array_key_exists</span>(<span $key</span>,<span $instance</span><span )){
</span><span  8</span>    <span $instance</span>[<span $key</span>]=<span new</span><span  SingletonExample();
</span><span  9</span> <span      }
</span><span 10</span>    <span return</span> <span $instance</span>(<span $key</span><span );
</span><span 11</span> <span   }
</span><span 12</span> 
<span 13</span> <span };
</span><span 14</span> ?>

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Reference material: PHP and mysql expert programming

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