Merge 3 arraylist to one

Question

I want to merge down 3 arraylist in one in java. Does anyone know which is the best way to do such a thing?

Answer 1

Use ArrayList.addAll(). Something like this should work (assuming lists contain String objects; you should change accordingly).

List<String> combined = new ArrayList<String>(); combined.addAll(firstArrayList); combined.addAll(secondArrayList); combined.addAll(thirdArrayList); 

Update

I can see by your comments that you may actually be trying to create a 2D list. If so, code such as the following should work:

List<List<String>> combined2d = new ArrayList<List<String>>(); combined2d.add(firstArrayList); combined2d.add(secondArrayList); combined2d.add(thirdArrayList); 

Answer 2

What about using java.util.Arrays.asList to simplify merging?

List<String> one = Arrays.asList("one","two","three"); List<String> two = Arrays.asList("four","five","six"); List<String> three = Arrays.asList("seven","eight","nine");  List<List<String>> merged = Arrays.asList(one, two, three);