Java: find empty key in map:

Question

I don't know why does not work with me. I have a empty keys in map but I cannot catch them.

Map<String, Long> map = new TreeMap<>();

//put data

map.entrySet().stream().forEach(e -> {
    if (e.getKey().equals("") || e.getKey().equals(" ") || e.getKey() == "" || e.getKey() == " ") {
        map.remove(e.getKey(), e.getValue());
    }
});

Edited: I made a test for value:

     map.entrySet().stream() .forEach(e -> {
            if (e.getValue() == 133835) {
            System.out.println("key empty: " + e.getKey().isEmpty());
            System.out.println("key: >" + e.getKey() + "<");
            System.out.println("val: " + e.getValue());
        }
    });

    map = map.entrySet().stream().filter(
            p -> !"".equals(p.getKey().trim())).
            collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));


map.entrySet().stream() .forEach(e -> {
    if (e.getValue() == 133835) {

        System.out.println("key empty: " + e.getKey().isEmpty());
        System.out.println("key: >" + e.getKey() + "<");
        System.out.println("val: " + e.getValue());
    }
});

the result is:

key empty: false
key: >‏<
val: 133835
key empty: false
key: >‏<
val: 133835

I think this key is a gost )

"I have a empty keys in map but I can catch them." - this sentence makes no sense. What are you trying to do, and what's happening instead of what you were trying to make happen? — user2357112
– user2357112, Commented Dec 11, 2014 at 21:54
can you specify what the issue is? what does not work for you? what are you expecting to happen? how do you put the data? — blurfus
– blurfus, Commented Dec 11, 2014 at 21:54
From the edit, it seems he can'T catch/find the keys that are empty strings in his map. — Sentry
– Sentry, Commented Dec 11, 2014 at 21:56
Obviously it's not empty. Figure out what's in it-where are the keys coming from. — Dave Newton
– Dave Newton, Commented Dec 11, 2014 at 23:10

dan b · Accepted Answer · 2014-12-11 22:27:07Z

1

Try using e.getKey().trim().isEmpty()

edited Dec 11, 2014 at 22:27

answered Dec 11, 2014 at 21:59

dan b

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3 Comments

Sam Joos Over a year ago

I have now just System.out.println("found") this is not the problem

Andreas Over a year ago

key.trim().isEmpty() sounds like the right way to check this. There may be exotic characters that are non-printing in your locale which trim() does not remove.

Sam Joos Over a year ago

It still the same result: key empty: false

wgitscht · Accepted Answer · 2014-12-11 23:19:54Z

0

first of all i would generally suggest to trim instead of checking for " " m(one space) and "" (empty string). And secondly that might be the case (a key with more than one space).

  "".equals(e.getKey().trim())

edit example: Map map = new TreeMap();

        map.put("",  1L);
        map.put(" ", 2L);
        map.put("3", 3L);

        map.entrySet().stream().forEach(e -> {
            System.out.println("key empty: " + e.getKey().isEmpty());
            System.out.println("key: >" + e.getKey() + "<");
            System.out.println("val: " + e.getValue());
        });
        map = map.entrySet().stream().filter(
                p -> !"".equals(p.getKey().trim())).
                collect(Collectors.toMap(Entry::getKey, Entry::getValue));        

        map.entrySet().stream().forEach(e -> {
            System.out.println("key empty: " + e.getKey().isEmpty());
            System.out.println("key: >" + e.getKey() + "<");
            System.out.println("val: " + e.getValue());
        });

output is:

key empty: true
key: ><
val: 1
key empty: false
key: > <
val: 2
key empty: false
key: >3<
val: 3
AFTER REMOVAL
key empty: false
key: >3<
val: 3

edited Dec 11, 2014 at 23:19

answered Dec 11, 2014 at 21:57

wgitscht

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12 Comments

Ingo Bürk Over a year ago

How does this answer the question?

wgitscht Over a year ago

deosn't answer it but might be a lead in the right direction. for me it appears an empty key for him is defined as an String matching one blank or "". So maybe a String with two bnalks qulifies as empty as well and will not be fdund by his code.

wgitscht Over a year ago

tried a filter?, something like:

m.entrySet().stream()     .filter(p ->  !"".equals(p.getKey().trim()))     .collect(toMap(Entry::getKey, Entry::getValue));

Sam Joos Over a year ago

How can I make this mothod toMap() ?

wgitscht Over a year ago

sry: Collectors.toMap (disclaimer: have not java8 compiler at hand).

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