java arraylist of arraylist

/**
 * Java example:  arraylist in arraylist
 */

import java.util.*;
import java.time.*;

public class Lautturi {
	public static void main(String[] args) {
		  ArrayList<ArrayList<Integer>> outer = new ArrayList<ArrayList<Integer>>();
		    ArrayList<Integer> inner = new ArrayList<Integer>();        

		    inner.add(100);     
		    inner.add(200);
		    outer.add(inner); // add first list
		    inner = new ArrayList<Integer>(inner); // create a new inner list that has the same content as the orlautturinal inner list
		                                          
		    outer.add(inner); // add second list

		    outer.get(0).add(300); // changes only the first inner list

		    System.out.println(outer);
	}
}