General Java Questions II

For example:

public void recurseList( List l )

the generic List ensure that you can use every List for this method (ArrayList,

AbstractList, Vector...), so your calling method can be:

ArrayList l = new ArrayList(); or

Vector l = new Vector();

recurseList( l );

Without any problem.

by Davide Bianchi

 Q: I got a problem with an array/vector...

I got a problem with an array/vector.

my class contains a member:

static Vector quad[][];

....

in my constructor I got:

Vector quad[][] = new Vector[row][col];

for (int i = 0; i < row; i++){

   for (int j = 0; j < col; j++){

      quad[i][j] = new Vector (0,1);

   }

}

// row and col are int between (10..50)    it s a big I know, but that

might not be the problem

My PROBLEM (and I don t know what to do, really), I can t access quad[x][y] outside

of the constructor!!!! Within the constructor I ve got full access on quad[x][x]. Java

(1.2) returns a NullPointerException on any method except within the constructor!!!

What s my fault!???

Answer: I guess you shouldn t write Vector here:

Vector quad[][] = new Vector[row][col];

so, the correct variant may be:

quad[][] = new Vector[row][col];

I guess You just overridden your static variable with one defined in your constructor:

Vector quad[][].

Thus, you re initializing NOT your class scope static variable but your

constructor scope quad. It s not reachable outside the constructor. And as for static

quad, it has never been initialized! And a first reference to it causes

NullPointerException. I guess. I hope I m right :)

Xao Rom

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