Solved

Avoiding static

Posted on 2002-06-11
4
179 Views
Last Modified: 2010-03-31

I have an array which is instantiated in one class, and referenced in a few others. If I declare
the array static everyting compiles and runs, but references to the array give me erratic
performance.

Removing the static declaration results in the following compiler error:

"Can't make a static reference to nonstatic variable entryforms in class InstantiatingClass.
               method( InstantiatingClass.entryforms[ i ].someVariable, ... );"
                                                                                          ^
What adjustments do I make to the outside references in order to keep the array declaration non-static?


A little more detail: -----------------------------------------------------------------------
[code]
class InstantiatingClass extends MouseAdapter {

     static EntryForm[] entryforms;     //     This compiles but gives screwy results
     EntryForm[] entryforms;          //     References to this do not compile
     
     ...
     
     entryforms = new EntryForm[15];    
     ...
}


class ReferrringClass extends MouseAdapter {

...

EntryForm[] entryforms;
     
     public ReferrringClass( EntryForm[] entryforms ) {
                         
          this.entryforms = entryforms;

     }

          for( int j = 0; j < 15; j++ ) {
               if( e.getSource() == entryforms[j].submitButton ) {
                   
                    i = j;                                                  //     "i" is the INSTANCE of the form
                    break;
               }
          }
          ...
                         
          if ( entryforms[ i ].someVariable == "Something" ) {     // Results in null pointer errors at runtime          
                         
          if ( InstantiatingClass.entryforms[ i ].someVariable == "Something" ) {     // References like these result in compiler errors          
          ...
                             
          }

}
[/code]
Many thanks in advance.
0
Comment
Question by:javaQQ
  • 2
4 Comments
 
LVL 35

Accepted Solution

by:
girionis earned 50 total points
ID: 7070666
 If your variable is not static you cannot call it like:

 InstantiatingClass.entryforms[ i ].someVariable

  instead you will need to create a reference to the class and call it (if it is public) through the reference:

  InstantiatingClass ic = new InstantiatingClass();
  ic.entryforms[i].someVariable;

  Hope it helps.
0
 
LVL 92

Assisted Solution

by:objects
objects earned 50 total points
ID: 7071388
> if ( entryforms[ i ].someVariable == "Something" ) {
> // Results in null pointer errors at runtime          

Sounds like you haven't initialised entryForms correctly.
0
 
LVL 9

Expert Comment

by:Ovi
ID: 7072003
You can implement the singleton pattern, like this :

public final class ArrayClass {
  private static final ArrayClass arrayClassObject = null;
  EntryForm[] entryforms = new EntryForm[20];

  private ArrayClass() {
    //do some init...
  }

  public static final ArrayClass getArrayClassObject() {
    if(arrauClassObject == null)
      arrayClassObject = new ArrayClass();
    return(arrayClassObject);
  }
}


After that you should be able to use'it from any point like this :
ArrayClass.getArrayClassObject().entryForms;
or
ArrayClass.getArrayClassObject().entryForms[0];
ArrayClass.getArrayClassObject().entryForms[1];
ArrayClass.getArrayClassObject().entryForms[2];

0
 
LVL 35

Expert Comment

by:girionis
ID: 8834385
No comment has been added lately, so it's time to clean up this TA.

I will leave a recommendation in the Cleanup topic area that this question is:

- split points between girionis and objects@idg

Please leave any comments here within the
next seven days.

PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER !

girionis
Cleanup Volunteer
0

Featured Post

Problems using Powershell and Active Directory?

Managing Active Directory does not always have to be complicated.  If you are spending more time trying instead of doing, then it's time to look at something else. For nearly 20 years, AD admins around the world have used one tool for day-to-day AD management: Hyena. Discover why

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Java Timer (static) 9 43
servlet requestdispatcher include and forward differences 1 30
java jdbc batch example 8 34
printf performancy 11 42
INTRODUCTION Working with files is a moderately common task in Java.  For most projects hard coding the file names, using parameters in configuration files, or using command-line arguments is sufficient.   However, when your application has vi…
This was posted to the Netbeans forum a Feb, 2010 and I also sent it to Verisign. Who didn't help much in my struggles to get my application signed. ------------------------- Start The idea here is to target your cell phones with the correct…
Viewers learn about the “while” loop and how to utilize it correctly in Java. Additionally, viewers begin exploring how to include conditional statements within a while loop and avoid an endless loop. Define While Loop: Basic Example: Explanatio…
Viewers will learn about the different types of variables in Java and how to declare them. Decide the type of variable desired: Put the keyword corresponding to the type of variable in front of the variable name: Use the equal sign to assign a v…

777 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question