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"cannot assign a value to final variable"

Posted on 2004-05-01
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Last Modified: 2012-06-22
i've got 2 classes:

public interface Constants {
  public static final int     MAX_LIGHTS = 10;
  public static final int     MAX_SOLIDS = 100;

  static Vector Eye         = new Vector ( 0, 0, 0 );         // camera position
  static Vector EyeDir      = new Vector ( 0, 0, 1 );         // viewing directing ( normal to image plane )
  static Vector Vx          = new Vector ( 1, 0, 0 );         // image plane basis - horizontal vector
  static Vector Vy          = new Vector ( 0, 1, 0 );         // vertical vector
}

public class Tracer implements Constants
{
  public Tracer () { }
 
  public static void SetCamera ( Vector Org, Vector Dir, Vector UpDir ) {
    Eye    = Org;                    // eye point
    EyeDir = Dir;                    // viewing direction
    Vx     = Vx.Normalize ( UpDir.Power ( UpDir, Dir ) );  // build orthogonal basis of image plane
    Vy     = Vy.Normalize ( Dir.Power ( Dir, Vx ) );    // EyeDir orthgonal to this basic ( image plane )
  }
}

when i try to compile it, it gives me this error:

D:\Program Files\Xinox Software\JCreatorV3 LE\MyProjects\ajajai\src\Tracer.java:35: cannot assign a value to final variable Eye
    Eye    = Org;                    // eye point

but why compiler claims that variable Eye is final? i'm sure it is not final, it's only static. where is the problem??
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Question by:tigrine_smiltpele
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4 Comments
 
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Expert Comment

by:krakatoa
ID: 10967458
I thnk because it's already been defined in the interface that Tracer implements, which means to all intents that it was defined as a static member of Tracer, and now you are trying to redefine it.

The same compiler error would happen for example if you said "this=null;" inside a class constructor.
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LVL 7

Expert Comment

by:maheshexp
ID: 10968100
>>but why compiler claims that variable Eye is final? i'm sure it is not final, it's only static. where is the problem??

fields defined inside a Interface are always "final" fields, and cannot be changed during runtime
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Accepted Solution

by:
maheshexp earned 50 total points
ID: 10968115
so try using abstract class

public abstract class Constants {
  public static final int     MAX_LIGHTS = 10;
  public static final int     MAX_SOLIDS = 100;

  static Vector Eye         = new Vector ( 0, 0, 0 );         // camera position
  static Vector EyeDir      = new Vector ( 0, 0, 1 );         // viewing directing ( normal to image plane )
  static Vector Vx          = new Vector ( 1, 0, 0 );         // image plane basis - horizontal vector
  static Vector Vy          = new Vector ( 0, 1, 0 );         // vertical vector
}

public class Tracer extends Constants
{
  public Tracer () { }
 
  public static void SetCamera ( Vector Org, Vector Dir, Vector UpDir ) {
    Eye    = Org;                    // eye point
    EyeDir = Dir;                    // viewing direction
    Vx     = Vx.Normalize ( UpDir.Power ( UpDir, Dir ) );  // build orthogonal basis of image plane
    Vy     = Vy.Normalize ( Dir.Power ( Dir, Vx ) );    // EyeDir orthgonal to this basic ( image plane )
  }
}

hope it will work now
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LVL 7

Expert Comment

by:maheshexp
ID: 10969796
thanks :-)
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