• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 319
  • Last Modified:

global variables

Hi:

I wrote some classes under a folder. I also have the other classes (with package declaration) in various packages under the same folder. So the structure is like:
MyFolder
- (default package)
    --MyPublicStaticVariablesClass.java
    --...
- packageA
- packageB

My question are:
1. how can I use a variable in the MyPublicStaticVariableClass in default package from packageA?
2. what is the best way to declare global variables if I prefer to export only package level files when making executables?
 
0
sdc248
Asked:
sdc248
  • 4
  • 3
  • 2
  • +3
2 Solutions
 
StillUnAwareCommented:
1. simply add this line:

import packageA.*;

2. This question is more trickier, are You using some IDE while developing an app? (like eclipse or NetBeans or any other?)
0
 
sdc248Author Commented:
1. import packageA from MyPublicStaticVariablesClass? But I am referencing variables in that class FROM packageA, not the other way around.
2. I am using elicpse.
0
 
StillUnAwareCommented:
As for the first part of Your question:
You should be able to use the class MyPublicStaticVariablesClass in any other classes without importing any packages, as long the java application starting directory path is the one where the MyPublicStaticVariablesClass class is contained. In other words:

class A {
    ... main(...) {}
}
======
package p;
class B {
    ... f(...) {
        A a = new A(...);
    }
}

The class tructure above should work without any additional imports as long as You run the starting application from top directory. Say this way:

java A
0
Get expert help—faster!

Need expert help—fast? Use the Help Bell for personalized assistance getting answers to your important questions.

 
CEHJCommented:
Use of the default package is not recommended, particularly when other parts of your tree *are* in packages
0
 
sdc248Author Commented:
I thought so too. But I got "A cannot be resolved to a type" from eclipse...
0
 
Mayank SAssociate Director - Product EngineeringCommented:
Can you post your complete project/ package/ class hierarchy?
0
 
sdc248Author Commented:
Hi CEHJ:

So the better to make it work is to put those "global" files in another package and then have it imported from the 'client" packages?

Do I simply create a new package,move all the files in it, and add the package declarations? (Want confirmation because they are soruce codes for a couple of running applications.)
0
 
CEHJCommented:
>>So the better to make it work is to put those "global" files in another package and then have it imported from the 'client" packages?

I would do yes. Make, say, a 'constants' package
0
 
objectsCommented:
> 1. how can I use a variable in the MyPublicStaticVariableClass in default package from packageA?

you can't

> 2. what is the best way to declare global variables if I prefer to export only package level files when making executables?

They *must* go in packages

0
 
Mayank SAssociate Director - Product EngineeringCommented:
To make things simpler, can you please reply to: >> "Can you post your complete project/ package/ class hierarchy?"
0
 
astorerCommented:
>> 1. how can I use a variable in the MyPublicStaticVariableClass in default package from packageA?
import MyPublicStaticVariableClass;

from your class in packageA.
Then can use
    MyPublicStaticVariableClass.globalVar
or better
    MyPublicStaticVariableClass.getGlobalVar()
Remember that globalVar or getGlobalVar() must be public and static

I would say that MyPublicStaticVariableClass should not be in the default package anyway.  Why not just put into a package called statics or util ?

>> 2. what is the best way to declare global variables if I prefer to export only package level files when making executables?
There is no such thing as a global variable in an Object Oriented programming language.
What you do have is static members on a class.  That means that there is only one of these and you access via Class.member (rather than object.member).
These can be used as though they are global variables.

If pushed I'd use:

package statics;
public class MyPublicStaticVariableClass {
  private static String myVar = null;
  public static String getMyVar(){
      return myVar;
  }
  public static void setMyVar(String myVarParam){
      myVar = myVarParam;
  }
}

Then whenever you want to use MyVar
  String x = statics.MyPublicStaticVariableClass.getMyVar()
  statics.MyPublicStaticVariableClass.setMyVar("ABC");

Andrew



 
0
 
sdc248Author Commented:
Thank you guys for your help. I am putting all shared variables in a class in a seperate package.

p.s.
I tried "import MyPublicStaticVariableClass;" but that didn't work. That class is not visable from packageA.
I did not post my whole project/package/class hierarchy because I think the brief structure provided in the question has provided enough information for problem identification/solving.
0
 
CEHJCommented:
:-)
0
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Featured Post

Keep up with what's happening at Experts Exchange!

Sign up to receive Decoded, a new monthly digest with product updates, feature release info, continuing education opportunities, and more.

  • 4
  • 3
  • 2
  • +3
Tackle projects and never again get stuck behind a technical roadblock.
Join Now