CODEWITHSUNDEEP
javagenericsarraylist
CodedRoses
CodedRoses

Reputation: 81

How to Properly Setup Generic ArrayLists in Java (based on SkipLists)

I'm trying to code up SkipLists as I just learned about the data structure.

Main Question: How do I properly setup a Generic ArrayList for SkipLists?

So far, I've learned java does not like generic arrays for example:

SkippyList.java:138: error: generic array creation
                SkipNode<T>[] criticalPoints = (SkipNode<T>[]) new SkipNode<T>[height];

So now I'm trying to use ArrayLists to hold these generic types. I've been scouring the internet and haven't been able to find a solution that works. I've tried setting up the ArrayList (as a global variable) like ArrayList<SkipNode<AnyType>>[] next;

Then in a function such as this one declare it like such:

    // Constructor for a node with data, but not wired in.
    public SkipNode(AnyType data, int height)
    {
        this.data = data;
        this.height = height;
        this.next = new ArrayList<SkipNode<AnyType>>[height];
        for (int i = 0; i <= height; i++)
            this.next[i] = null;
    }

But then I end up with another error such as this one:

SkippyList.java:14: error: generic array creation
                this.next = new ArrayList<SkipNode<AnyType>>[height];

For reference the (not updated) constructor for (some) of the nodes:

    // Constructor for the head node
    public SkipNode(int height)
    {
        this.data = null;
        this.next = (SkipNode<AnyType>[]) new SkipNode[height];
        for (int i = 0; i <= height; i++)
            this.next[i] = null;
    }

I know it is possible, do I need to include the <AnyType> (because I've tried to leave it off and still recieve the same result) or am I just improperly creating a Generic ArrayList?

Thank you for any insight!

Upvotes: 0

Views: 99

Answers (1)

Bill Mair
Bill Mair

Reputation: 1151

Wrong brackets :-)

You are trying to create an array "ArrayList[arraySize]" instead of an instance of ArrayList with an initial size

new ArrayList<SkipNode<AnyType>>[arraySize];

I think what you are trying to do is

new ArrayList<SkipNode<AnyType>>(someInitialListSize);

But without knowing exactly what type "this.next" is (maybe it really is SkipNode[]?), it is hard to be sure.

Upvotes: 1

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