Cannot create an array of LinkedLists in Java...?

java arrays generics
kafuchau picture kafuchau · Oct 20, 2008 · Viewed 72.1k times · Source

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

Fredrik picture Fredrik · Oct 20, 2008

For some reason you have to cast the type and make the declaration like this:

myMatrix = (LinkedList<IntegerNode>[]) new LinkedList<?>[numRows];

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