I have a list of Integer values named list, and from the list.stream() I want the maximum value.
What is the simplest way? Do I need a comparator?
11 Answers
You may either convert the stream to IntStream:
OptionalInt max = list.stream().mapToInt(Integer::intValue).max(); Or specify the natural order comparator:
Optional<Integer> max = list.stream().max(Comparator.naturalOrder()); Or use reduce operation:
Optional<Integer> max = list.stream().reduce(Integer::max); Or use collector:
Optional<Integer> max = list.stream().collect(Collectors.maxBy(Comparator.naturalOrder())); Or use IntSummaryStatistics:
int max = list.stream().collect(Collectors.summarizingInt(Integer::intValue)).getMax(); 
9 Comments
Roland
Would be interesting to know which one is more efficient.
elect
May I ask why, Tagir?
Tagir Valeev
@elect, it first unboxes all the integers, then compares the unboxed ones. 2nd, 3rd and 4th solutions do the unboxing on each comparison effectively doing twice as much unboxing operations. The last one computes more statistics (like sum and min) which is unnecessary here, but will surely take some time.
Andrejs
If you want to just get an
int, then mapToInt(...).max().getAsInt() or reduce(...).get() to the method chainsTagir Valeev
@Bogdan, this is solveable, though apparently was not required in question. Nevertheless you can post your own answer covering this situation.
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int max = list.stream().reduce(Integer.MIN_VALUE, (a, b) -> Integer.max(a, b)); 
2 Comments
rolika
This works only, if all of your values are positive. Use Integer.MIN_VALUE instead of 0 in reduce().
Piotr Supel
Could also be int max = list.stream()reduce(Integer.MIN_VALUE, Integer::max);
Another version could be:
int maxUsingCollectorsReduce = list.stream().collect(Collectors.reducing(Integer::max)).get(); 
Comments
Correct code:
int max = list.stream().reduce(Integer.MIN_VALUE, (a, b) -> Integer.max(a, b)); or
int max = list.stream().reduce(Integer.MIN_VALUE, Integer::max); 
Comments
You can also use below code snipped:
int max = list.stream().max(Comparator.comparing(Integer::valueOf)).get(); Another alternative:
list.sort(Comparator.reverseOrder()); // max value will come first int max = list.get(0); 
Comments
int value = list.stream().max(Integer::compareTo).get(); System.out.println("value :"+value ); 
1 Comment
help-info.de
There are other answers that provide the OP's question, and they were posted many years ago. When posting an answer, please make sure you add either a new solution, or a substantially better explanation, especially when answering older questions.
I think another easy way is
IntSummaryStatistics statistics = List.of(1, 2, 3).stream() .mapToInt(Integer::intValue) .summaryStatistics(); int max = statistics.getMax(); With this you can also getMin() amd other stuff like mean. A SummaryStatistics Object can be created from other Streams by supplying appropriate parameters.
Comments
With stream and reduce
Optional<Integer> max = list.stream().reduce(Math::max); 1 Comment
Didier L
It seems you posted this answer twice and removed the other one, but as I commented on the other one, this solution is already included in Tagir's answer (with
Integer::max but that's exactly the same).you can also find the max element in a collection using bellow code:
List<Integer> intList = Arrays.asList(1, 2, 3, 4, 5, 6, 7); Optional<Integer> max = intList.stream().max((a, b) -> a - b); 
1 Comment
user85421
a - b is dangerous because of integer overflow → Arrays.asList(-2147483640, 100).stream().max((a, b) -> a - b) will result in Optional[-2147483640] but -2147483640 is not greater than 100In my case, need to convert a String (SeqNum) to integer and find a max value of it.
list.stream().map(TxnCharges::getSeqNum) .max(Comparator.comparingInt(s -> Integer.parseInt(s.trim()))) .orElse(null); 
1 Comment
user85421
more Stream-like:
list.stream().map(TxnCharges::getSeqNum).map(String::trim).mapToInt(Integer::parseInt).max().orElse(0) (but not applicable to List<Integer> as asked for)
Collections.max..