Using a variable outside of forEach loop

Question

I'm new to java and I'm tinkering with forEach loops.

I want to use entry.getValue() outside of the loop like this:

hashmap.entrySet().stream()
    .sorted(Map.Entry<String,Double>comparingByValue())
    .limit(1).forEach(entry->
        {System.out.print("Worst output: " + entry.getValue() + ");}
    );
....//print the one iteration of previous loop, or use entry.getValue() as var

Just to be certain - you're looking for the lowest value in the map? — Mureinik
– Mureinik, Commented Feb 11, 2017 at 15:01
You shouldn't sort, and should't limit, and shouldn't use forEach to find the minimum value. Instead, you should use min(): docs.oracle.com/javase/8/docs/api/java/util/stream/… — JB Nizet
– JB Nizet, Commented Feb 11, 2017 at 15:03
I repeat: you shouldn't have any forEach loop. To find the min() value of a stream, use the min() method. Not sort() followed by limit() followed by forEach. — JB Nizet
– JB Nizet, Commented Feb 11, 2017 at 15:11
This looks like X/Y problem. @Heist you can't use variable outside of its declared scope (in this case lambda). So what you are asking is impossible. But you can use its value, for instance by returning it like in case of min() method already mentioned here. — Pshemo
– Pshemo, Commented Feb 11, 2017 at 15:11

Elliott Frisch · Accepted Answer · 2017-02-11 15:07:07Z

3

I believe you want to map your entries to double and then use DoubleStream.min() with something like,

double worst = hashmap.entrySet().stream()
        .mapToDouble(Map.Entry<String,Double>::getValue).min().getAsDouble();
System.out.println("Worst output: " + worst);

If you actually want the maximum value use max() instead of min().

answered Feb 11, 2017 at 15:07

Elliott Frisch

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3 Comments

Heist Over a year ago

Can i get the corresponding key to that value, and put it in something like String w = ...

Buhb Over a year ago

This will throw NoSuchElementException in the case of an empty map. The original code would simply not print anything.

Holger Over a year ago

You don’t need to map with Map.Entry<String,Double>::getValue, if you stream over values() rather than entrySet() in the first place. And if we don’t stream, the classical solution is as simple as double worst = Collections.min(hashmap.values());

Mureinik · Accepted Answer · 2017-02-13 16:33:04Z

2

You could simply use the max method to get the highest value:

Double max = hashmap.values()
                    .stream()
                    .max(Comparator.naturalOrder())
                    .orElse(null);

edited Feb 13, 2017 at 16:33

answered Feb 11, 2017 at 15:08

Mureinik

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2 Comments

Buhb Over a year ago

This doesn't compile

Mureinik Over a year ago

@Buhb stupid copy-paste mistake, thanks - edited and fixed.

Buhb · Accepted Answer · 2017-02-13 19:34:32Z

2

If you want to do something with the entire Map.Entry, and also elegantly handle empty maps, I suggest you do it with Optional.

Optional<Map.Entry<String, Double>> o = hashmap.entrySet().stream().min(Map.Entry.comparingByValue());
o.ifPresent(entry -> System.out.println(entry.getKey() + " " + entry.getValue()));

This way, if there is at least one entry in the map, the lowest one is returned, and since it's wrapped in an optional, you can easily handle the empty case as well. In the sample code above, it will print both the key and the value, if it's present, or do nothing if it isn't.

edited Feb 13, 2017 at 19:34

answered Feb 11, 2017 at 15:21

Buhb

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