Vector引起的java.lang.NullPointerException

Question

I 'm using a matrix where each element is a vector of object "Person". I defined my Person class.

In an other class (and in the same package), I declared ma matrix as the following:

Vector<CKYCell> [] [] Score= new Vector [length][length];

I want to know the size of each element of the matrix, I use:

System.out.println(Score[i][i].size());

But I have the following error:

java.lang.NullPointerException

Is there any one who could help me. Thanks in advance.

Answer 1

Vector [][] is an array of nulls. You need to allocate that actual vectors and stuff them into the array.

Answer 2

The problem is that you create a 2 dimensional array of Vector s here:

Vector<CKYCell> [] [] Score= new Vector [length][length];

but you leave it empty. The first time you try to dereference an item in it: Score[i][i] you will get the default value form the array which is null .

To add an item to your array you can simply do something like this: Score[i][i] = myItem;

Keep in mind that Score does not refer to a Vector but an array containing Vector s . Vector objects are also considered to be deprecated in most cases.