float的arraylist的arraylist的Java初始值

Question

Given the below code

ArrayList<ArrayList<Float>> fWordTagProb = new ArrayList<ArrayList<Float>>();
for(int f=0;f<pennTreeTags.size();f++)
    fWordTagProb.add(new ArrayList<Float>());

What is the initial value of each "cell" in this 2d array? Is it zero?

Hence is it the same for type Integer?

Thanks in advance for the help

Answer 1

Each element of fWordTagProb is an empty ArrayList . Logically there are nothing yet in the empty lists.

It would be same if you used Integer instead of Float .

Answer 2

The cells are boxed Floats, and so are reference types. The default value of a reference type is null , and so too is the default value of each cell.

I should add that the sub-ArrayLists are empty, and so there aren't actually any cells at all. Should the sub-lists be initialized to the desired size, then the cells will indeed be null .