How do I get length of list of lists in Java?

Question

If I have a List<List<String>> data in Java, I can get the length of the first list via code:

int lengthData = data.get(0).size(); 

But how do I get the number of lists in the structure without traversing the list of lists to find out?

Maybe I've been a bit unclear. I have the structure:

List<List<String>> data  

And I see that:

int i = data.size(); 

Will equal 1 because it is the root list. So what I want to know is how many sublists there are. Traversal of the structure like this:

for (List<String> l : data) {                           total ++;                 } 

Only gives me a result of 1 which I find odd.

I have data of the form:

List 1 ==> 1, 2, 3, 4 List 2 ==> 3, 8. 9, 1 

And so on where these are sublists of the root list.

Answer 1

Just use

int listCount = data.size(); 

That tells you how many lists there are (assuming none are null). If you want to find out how many strings there are, you'll need to iterate:

int total = 0; for (List<String> sublist : data) {     // TODO: Null checking     total += sublist.size(); } // total is now the total number of strings 

Answer 2

Java 8

import java.util.Arrays; import java.util.List; import java.util.ArrayList;  public class HelloWorld{       public static void main(String []args){             List<List<String>> stringListList = new ArrayList<>();             stringListList.add(Arrays.asList(new String[] {"(0,0)", "(0,1)"} ));             stringListList.add(Arrays.asList(new String[] {"(1,0)", "(1,1)", "(1,2)"} ));             stringListList.add(Arrays.asList(new String[] {"(2,0)", "(2,1)"} ));              int count=stringListList.stream().mapToInt(i -> i.size()).sum();              System.out.println("stringListList count: "+count);      } }