Assume a list:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);

Approach 1: Using Streams

boolean isSorted = IntStream.range(0, numbers.size() - 1)
    .allMatch(i -> numbers.get(i) <= numbers.get(i + 1));

System.out.println(isSorted);

Output:

true

Approach 2: Using List.equals() with a sorted copy

boolean isSorted = numbers.equals(
    numbers.stream().sorted().collect(Collectors.toList())
);

System.out.println(isSorted);

Output:

true