how to create nested linked list List<List<Integer>>

// 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(); 
        } 
    } 
}