[请教] constants define in java package ！！！

carol1980

Hi, All

Have a question about java.

1. How do you usually define constants with a package?
   
2. 
   
3. The only solution I can find is to define an "Constants Interface" like this:
   
4. interface Constants
   
5. {
   
6.    static final public int SUCCESS=1;
   
7.    static final public int FIAL=0;
   
8.    ... ...
   
9. }
   
10. Then, every class in the package  using these constants has to implement this interface.
    
11. 
    
12. An abstract final class defining these constants is an alternative, but then I have to site the class name when using the constants, like this:
    
13. if( dosth()==Constant.SUCCESS)
    
14. {... ...}
    
15. 
    
16. I'm wondering if there is any other better solutions to define package constants?  You know, Im some kind of new comer to java but am involved in a java project now.

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dennis2

Should be OK. Actually tomcat's javax.servlet.* implementation is doing exactly that. Take a look at jakarta-tomcat-5.0.16-src/src/jakarta-servletapi-5/jsr154/src/share/javax/servlet/http/HttpServletResponse.java , the http status codes are all defined that way.

Beware that those are defined in a specific interface (in the above case, the HttpServletResponse interface), not in a global Constant interface. But I think where to define the constants really depends on the actual situation.

carol1980

Thank you for your reply

elgs

In the forth coming Java 1.5, there will be an exciting feature, static import. You may take a look at it.

http://java.sun.com/features/2003/05/bloch_qa.html

elgs

The static import facility offers a clean alternative. It lets the programmer avoid qualifying static member names without subtyping. It's analogous to the package import facility, except that it imports static members from a class, rather than classes from a package. Here's how it looks:

1. 
   
2. import static org.iso.Physics.*;
   
3. 
   
4. class Guacamole {
   
5.     public static void main(String[] args) {
   
6.         double molecules = AVOGADROS_NUMBER * moles;
   
7.         ...
   
8.     }
   
9. }
   

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Note that this works whether Physics is an interface or a class. If it just defines constants, it should definitely be a class rather than an interface.