General Java Questions I

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

Q: I propose that Java should allow multiple inheritance if...

Everyone knows the potential problem with multiple inheritance is when you run into

the problem of having two instances of a grand parent super class.

For example:

class A extends D {int i; }

class B extends D {int i; }

class C extends A,B {}

Potentially, you could have two copies of D for each instance of C.

However, I propose that Java should allow multiple inheritance if there are no

instance variables associated with the abstracts that the base class is extending.

abstract class A { public setX(); public setY(); public setAll() {setX (); setY(); }

abstract class B { public setC(); public setD(); public setBoth()

{setC(); setD(); }

class C extends A,B {}

You won t have two instances of some grandfather class, since A and B doesn t have

instances variables.

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