Clever Geek Handbook

Java8 how to create nested lists?

Learn and play with Java8. Trying to create a 2D array.

final List<Integer> row = IntStream.range(0, 3)
                                   .boxed()
                                   .collect(Collectors.toList());

List<List<Integer>> arr2D = IntStream.range(0, 3)
                                     .map(i -> arr2D.add(i, row)); // will not compile

how to put string into 2D array? and is this the correct way to use Java8?

+3


source to share


2 answers


Your question mentions arrays, but your code only has lists. If you want to create a nested list:

List<List<Integer>> arr2D = IntStream.range(0, 3)
                                     .mapToObj(i -> row)
                                     .collect(Collectors.toList());


Of course, with this code, all internal lists will be identical (i.e. the same instance). If you want each inner list to be a different instance:

List<List<Integer>> arr2D = IntStream.range(0, 3)
                                     .mapToObj(i -> new ArrayList<Integer>(row))
                                     .collect(Collectors.toList());
+6


source


The solution could be:



List<List<Integer>> lists = IntStream.range(0, 3)
                                     .mapToObj(i -> IntStream.range(0, 3)
                                                             .mapToObj(j -> j)
                                                             .collect(Collectors.toList()))
                                     .collect(Collectors.toList());
+2


source






More articles:


All Articles