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  does an import statement really load the class?  (Read 1261 times)
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Offline emzic

Senior Devvie





« Posted 2008-02-28 16:32:33 »

hello, i was wondering if an import statement forces the class to be loaded, even when that class is never used?

example:

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import java.awt.Point;

public class Dummy {

 public static void main(String[] args) {
  // do nothing
 }

}


will the java.awt.Point class be loaded even though it is never used?

thanks!

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Offline Orangy Tang

JGO Kernel


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« Reply #1 - Posted 2008-02-28 18:11:42 »

IIRC, no - import statements are simply a compile-time shortcut to prevent you having to type the fully qualified class name (eg. com.java.Foo ) every time you use something.

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Offline Riven
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Hand over your head.


« Reply #2 - Posted 2008-02-28 18:14:57 »

That's correct, import statements do NOT load the classes.



I can compile an application, remove some classes from the JAR, ensure the methods requiring those classes are not invoked, and everything still runs. They are indeed a convenience for the programmer, and have no meaning after compilation.

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Offline cylab

JGO Ninja


Medals: 55



« Reply #3 - Posted 2008-02-28 20:09:45 »

A class isn't even loaded before it is accessed at runtime, so in
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public class MySingleton
{  
     // Wrapped singleton instance
     private static class InstanceHolder {  
         static MySingleton instance = new MySingleton();  
     }  
   
     // Lazy initialization, no synchronization  
     public static MySingleton getInstance() {  
         return InstanceHolder.instance;  
     }  
}


The singleton instance is created when calling "return InstanceHolder.instance;", because the InstanceHolder class wasn't loaded until then. 

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Offline emzic

Senior Devvie





« Reply #4 - Posted 2008-02-29 13:53:10 »

thank you all for your answers!

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