(Java 8) I have an ArrayList of ArrayLists as follows:
[5, 10]
[2, 11]
[1, 12]
[8, 13]
I want these lists to be sorted by the first value in the list in either ascending or descending order. For example, with ascending order, the ArrayList would be ordered as:
[1, 12]
[2, 11]
[5, 10]
[8, 13]
How can I do this?
I am struggling with using the comparator class. Other documentation I have seen refers to when this data is represented by an array, (Arrays.sort then defining a comparator in the argument), but when it is a List of ArrayLists I cannot figure out the solution.
>Solution :
With a stream:
public static void main(String[] args) {
List<List<Integer>> list = new ArrayList<>();
list.add(asList(5, 10));
list.add(asList(2, 11));
list.add(asList(1, 12));
list.add(asList(8, 15));
List<List<Integer>> sorted = list.stream()
.sorted(Comparator.comparing(o -> o.get(0)))
.collect(Collectors.toList());
System.out.println("sorted = " + sorted);
}
private static List<Integer> asList(Integer... arr) {
return Arrays.asList(arr);
}
sorted = [[1, 12], [2, 11], [5, 10], [8, 15]]