二维数组的ArrayList

Question

I am able to declare variables dataList and data as follows:

ArrayList<Double[][]> dataList = new ArrayList<Double[][]>();
double [][] data = new double[2][];

but when I do something like

dataList.add(data);

I get an error saying

The method add(Double[][]) in the type ArrayList<Double[][]>
    is not applicable for the arguments (double[][])

How can I add data to dataList?

Answer 1

Declare your list to contain elements of type double[][] instead of Double[][] :

ArrayList<double[][]> dataList = new ArrayList<double[][]>();

This works because double[][] is not a primitive type, and hence can be the actual value for the generic type parameter for ArrayList .

Answer 2

You can do it with a ArrayList<double[][]> as Ted explained.

ArrayList<double[][]> dataList = new ArrayList<double[][]>();

The reason for the error is, double[][] is itself an Object, whereas Double[][] is an array of references to Double array of references to the Double objects.