public class My2DListImpl implements My2DList {
    int[][] data;
    public My2DListImpl(int sx,int sy) {
        // one way...
        data = new int[sx][sy];
        // another way...
        /*
        data = new int[sx][];
        for(int j=0;j<sx;j++)
            data[j] = new int[sy];
            */
    }
    public int get(int i1,int i2) {
        return data[i1][i2];
    }
    public int sizeX() { return data.length; }
    public int sizeY() { return data[0].length; }
    public void set(int i1,int i2,int value) {
        data[i1][i2] = value;
    }
    public static void main(String[] args) {
        My2DList m = new My2DListImpl(3,4);
        m.set(0,2,5);
        assert m.get(0,2) == 5;
        m.set(2,1,3);
        assert m.get(2,1) == 3;
        for(int j=0;j<m.sizeY();j++) {
            for(int i=0;i<m.sizeX();i++) {
                System.out.printf("%3d", m.get(i,j));
            }
            System.out.println();
        }
    }
}