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

List provides a method size() to get the count of elements currently present in the list. To get size of each list, we can use iterate through each item as list and add their sizes to get the count of all elements present in the list of lists. In this example, we are using streams to achieve the same.

Syntax

int size()

Returns the number of elements in this list. If this list contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Example

The following example shows how to check length of list of lists using size() method and streams.

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class CollectionsDemo {
   public static void main(String[] args) {
      List<Integer> list1 = new ArrayList<>(Arrays.asList(1,2,3));
      List<Integer> list2 = new ArrayList<>(Arrays.asList(4,5,6,7));
      List<Integer> list3 = new ArrayList<>(Arrays.asList(8,9));
      List<List<Integer>> list = new ArrayList<>(Arrays.asList(list1, list2, list3));
      int count = list.stream().mapToInt(i -> i.size()).sum();
      System.out.println("Total elements: " + count);
   }
}

Output

This will produce the following result −

Total elements: 9