ArrayList of ArrayList in Java Last Updated : 11 Dec, 2018 Improve Improve Like Article Like Save Share Report We have discussed that an array of ArrayList is not possible without warning. A better idea is to use ArrayList of ArrayList. // Java code to demonstrate the concept of // array of ArrayList import java.util.*; public class Arraylist { public static void main(String[] args) { int n = 3; // Here aList is an ArrayList of ArrayLists ArrayList<ArrayList<Integer> > aList = new ArrayList<ArrayList<Integer> >(n); // Create n lists one by one and append to the // master list (ArrayList of ArrayList) ArrayList<Integer> a1 = new ArrayList<Integer>(); a1.add(1); a1.add(2); aList.add(a1); ArrayList<Integer> a2 = new ArrayList<Integer>(); a2.add(5); aList.add(a2); ArrayList<Integer> a3 = new ArrayList<Integer>(); a3.add(10); a3.add(20); a3.add(30); aList.add(a3); for (int i = 0; i < aList.size(); i++) { for (int j = 0; j < aList.get(i).size(); j++) { System.out.print(aList.get(i).get(j) + " "); } System.out.println(); } } } Output: 1 2 5 10 20 30 Like Article Suggest improvement Previous Convert String into comma separated List in Java Next Office Tools and Domain Specific Tools Share your thoughts in the comments Add Your Comment Please Login to comment...