Question

I’m working on a sparse matrix class that needs to use an array of LinkedList to store the values of a matrix. Each element of the array (i.e. each LinkedList) represents a row of the matrix. And, each element in the LinkedList array represents a column and the stored value.

In my class, I have a declaration of the array as:

private LinkedList<IntegerNode>[] myMatrix; 

And, in my constructor for the SparseMatrix, I try to define:

myMatrix = new LinkedList<IntegerNode>[numRows]; 

The error I end up getting is

Cannot create a generic array of LinkedList<IntegerNode>.

So, I have two issues with this:

1. What am I doing wrong, and
2. Why is the type acceptable in the declaration for the array if it can’t be created?

IntegerNode is a class that I have created. And, all of my class files are packaged together.

Answer 1

You can’t use generic array creation. It’s a flaw/ feature of java generics.

The ways without warnings are:

1. Using List of Lists instead of Array of Lists:

   List< List<IntegerNode>> nodeLists = new LinkedList< List< IntegerNode >>(); 

2. Declaring the special class for Array of Lists:

   class IntegerNodeList {     private final List< IntegerNode > nodes; }