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

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 stru开发者_StackOverflowcture 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.

---

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

---

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);
     }
}

---

import java.util.ArrayList;

public class TestClass {

public static void main(String[] args) {

    ArrayList<ArrayList<String>> listOLists = new ArrayList<ArrayList<String>>();
    ArrayList<String> List_1 = new ArrayList<String>();
    List_1.add("1");
    List_1.add("2");
    listOLists.add(List_1);

    ArrayList<String> List_2 = new ArrayList<String>();
    List_2.add("4");
    List_2.add("5");
    List_2.add("10");
    List_2.add("11");
    listOLists.add(List_2);
    for (int i = 0; i < listOLists.size(); i++) {
        System.out.print("list " + i + " :");
        for (int j = 0; j < listOLists.get(i).size(); j++) {
            System.out.print(listOLists.get(i).get(j) + " ;");
        }
        System.out.println();
    }

}

}

I hope this solution gives a better picture of list if lists

---

count of the contained lists in the outmost list

int count = data.size();

lambda to get the count of the contained inner lists

int count = data.stream().collect( summingInt(l -> l.size()) );