Check in Map of list if exists value for specific key Java 8

Question

In Java 7 I have

Map<String, List<String>> m = new HashMap<String, List<String>>();
boolean result = false;
m.put("Name1", Arrays.asList("abc*1"));
m.put("Name2", Arrays.asList("abc@*1"));


for (Map.Entry<String, List<String>> me : m.entrySet()) {
    String key = me.getKey();
    List<String> valueList = me.getValue();
    if (key.equals("Name2"){
        System.out.print("Values: ");
        for (String s : valueList) {
            if(s.contains("@"){
                result = true;
            }
        }
    }
}

How can I get în a bool result for Name2 if it contains @ using any match?

I tried using The following Code but I Don t know how to use IT for specific key

result = m.values().stream().anyMatch(v -> v.contains("@"))

Did you mean if(s.contains("@"))? (Double quotes, not doubled apostrophes) — Bohemian
– Bohemian ♦, Commented Jun 6, 2018 at 10:14
You have If for if and '' (two apostrophes) instead of ". Is this code supposed to be compilable? — khelwood
– khelwood, Commented Jun 6, 2018 at 10:15

Nikolas · Accepted Answer · 2018-06-06 10:23:45Z

9

Do the following:

boolean result = m.getOrDefault("Name2", Collections.emptyList()).stream()
    .anyMatch(i -> i.contains("@"));

If the Map contains a correct key, check whether any of its element of the List as value contains the particular character. If the Map doesn’t contain the key, mock the empty Collection which doesn't contain anything at all and the result is evaluated automatically as false.

Edit: As @Michael suggested, using the Collections.emptyList() is a better choice than new ArrayList<>().

edited Jun 6, 2018 at 10:23

answered Jun 6, 2018 at 10:20

Nikolas

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6 Comments

Michael Over a year ago

This is the best way to do it. Why iterate over all of the keys when most maps are specifically designed to have a O(1) get?

Holger Over a year ago

@Michael Java 9 offers an in-between solution: Stream.ofNullable(m.get("Name2")) .flatMap(List::stream) .anyMatch(i -> i.contains("@"))

Michael Over a year ago

@Holger That's sufficiently different as to be worthy of its own answer, don't you think?

Holger Over a year ago

@Michael it’s different code, but not a fundamentally different logic, so I wouldn’t add an answer consisting of a small code snippet only. You can add it as an alternative to your answer, if you wish.

Holger Over a year ago

@Michael I have no objections against all these answers, but I don’t want to add another one. By the way, I see a fundamental difference. There are answers doing a linear iteration over the map and there are answers which avoid that.

|

Michael · Accepted Answer · 2018-06-06 10:36:54Z

7

You can simply use m.get("Name2"), place the (nullable) result into an Optional and then use a mapping:

boolean result = Optional.ofNullable(m.get("Name2"))
    .map(l -> l.stream().anyMatch(s -> s.contains("@")))
    .orElse(false);

This is preferable to looping over the entry set, as HashMap.get is O(1) and iterating over the entry set is O(n).

edited Jun 6, 2018 at 10:36

answered Jun 6, 2018 at 10:30

Michael

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2 Comments

Ousmane D. Over a year ago

the map should be .map(l -> l.stream().anyMatch(s -> s.contains("@")))

Holger Over a year ago

Better: Optional.ofNullable(m.get("Name2")) .filter(l -> l.stream().anyMatch(s -> s.contains("@"))) .isPresent()

Bohemian · Accepted Answer · 2018-06-06 10:29:56Z

2

Try this:

boolean result = m.entrySet().stream()
    .filter(e -> e.getKey().equals(Name2))
    .map(Map.Entry::getValue)
    .flatMap(List::stream)
    .anyMatch(s -> s.contains("@"));

answered Jun 6, 2018 at 10:29

Bohemian♦

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Comments

Youcef LAIDANI · Accepted Answer · 2018-06-06 12:46:27Z

2

What about

String name = "Name1";
boolean result= m.containsKey(name) && m.get(name).stream().anyMatch(a -> a.contains("@"));

edited Jun 6, 2018 at 12:46

answered Jun 6, 2018 at 10:19

Youcef LAIDANI

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Comments

Vinay Prajapati · Accepted Answer · 2018-06-06 10:15:03Z

1

Just add correct filter condition:

m.entrySet()
.stream()
.anyMatch(entry-> entry.getKey().equals(Name2) && 
   entry.getValue()
.stream()
.anyMatch(string -> string.contains("@"))
.getValue();

answered Jun 6, 2018 at 10:15

Vinay Prajapati

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Comments

Eran · Accepted Answer · 2018-06-06 10:17:27Z

1

First you should filter by the required key, then you can use anyMatch to determine if the value of that key contains an element with a '@' character:

result = m.entrySet ()
          .stream ()
          .filter (e->e.getKey ().equals (Name2))
          .anyMatch (e->e.getValue ().stream ().anyMatch (s->s.contains ("@")));

answered Jun 6, 2018 at 10:17

Eran

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Comments

Ousmane D. · Accepted Answer · 2018-06-06 10:25:47Z

1

create a stream from the entrySet() and then provide your criteria in the anyMatch:

result = m.entrySet()
          .stream()
          .anyMatch(v -> Objects.equals("Name2", v.getKey()) && 
               v.getValue().stream().anyMatch(s -> s.contains("@")));

or using getOrDefault:

result = m.getOrDefault("Name2", Collections.emptyList())
          .stream()
          .anyMatch(s -> s.contains("@"));

edited Jun 6, 2018 at 10:25

answered Jun 6, 2018 at 10:14

Ousmane D.

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