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How do you declare an ArrayList of lists in Java?

I need to build a class that will use an ArrayList of lists as a data structure. How do I declare such a data structure and how do I access their elements and the lists within the elements using Java?

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1. public static void main(String[] args) { List<List<String>> outter = new ArrayList<List<String>>(); List<String> inner1 = new ArrayList<String>(); inner1.add("Happy"); inner1.add("Halloween"); outter.add(inner1); List<String> inner2 = new ArrayList<String>(); inner2.add("What"); inner2.add("A Wonderful World"); inner2.add("Louis Armstrong"); outter.add(inner2); System.out.println("outter contains " + outter.size() + " inners"); System.out.println("inner1 says " + outter.get(0).get(0) + " " + outter.get(0).get(1)); System.out.println("inner2 sings " + outter.get(1).get(0) + " " + outter.get(1).get(1) + " by " + outter.get(1).get(2)); } OUTPUT: outter contains 2 inners inner1 says Happy Halloween inner2 sings What A Wonderful World by Louis Armstrong