General Java Questions III

 Q: Why developers should not write programs that call  sun  packages?

Answer: Java Software supports into the future only classes in java.* packages, not

sun.* packages. In general, API in sun.* is subject to change at any time without

notice. 

A Java program that directly calls into sun.* packages is not guaranteed to work on

all Java compatible platforms. In fact, such a program is not guaranteed to work

even in future versions on the same platform. 

For these reasons, there is no documentation available for the sun.* classes.

Platform independence is one of the great advantages of developing in the Java

programming language. Furthermore, Sun and our licensees of Java technology are

committed to maintaining backward compatibility of the APIs for future versions of

the Java platform. (Except for code that relies on serious bugs that we later fix.) This

means that once your program is written, the class files will work in future releases. 

For more details, see the article Why Developers Should Not Write Programs That

Call  sun  Packages. 

http://java.sun.com/products/jdk/faq/faq sun packages.html

Q: Can garbage collector remove my singleton?

A usually singleton..

public class Single{

   private static Single single;

   private Single {}

   public static Single getInstance(){

      if(single==null){

         single = new Single();

      }

      return single;

  }

}

Well,, seems good ?

But classes are objects too...so do Java 2 v1.3 class garbagecollecting? Meaning my

singleton could dissapear if i dont keep a refrence to it (or the class itself)

somewhere ?

If classes is not garbagecollected, that s pretty stupid, I dont want classes taking up

memory when i perhaps never will use it again....

Answer: No. Classes can define objects. That is, only the dynamic part of the class

defines objects. The static part exists only in one place in memory and can not be

duplicated. You can call the getInstance() method from anywhere in your program. 

Java requires however that you tell where to find the method, in this case in the

Single class.

Therefore, you should use

Single.getInstance()

to get the instance. This is (though it looks much like it) not an execution of a method

on an object, but just a method call without object. Single is only used to find out

which getInstance() method should be used, and where it is.

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