Java 8 Map: filter value and throw exception if match found

Question

I'm trying to find a matching value in a Map and if found, I need to throw an IllegalArgumentException. My code is as follows:

final String stringToBeMatched = "someRandomString"; 

map.values()
   .stream()
   .filter(a -> stringToBeMatched == a.getField())
   .findAny()
   .ifPresent(a -> throw new IllegalArgumentException());

I get a syntax error on token "throw". I'm not sure where I'm going wrong.

@khelwood: `ifPresent(a -> { throw new IllegalArgumentException(); })` — Holger, Apr 26 '16 at 17:49

rgettman · Answer 1 · 2016-04-26T15:11:23.673

31

A lambda body can be an expression or a block of statements. However,

throw new IllegalArgumentException()

is a statement, which is neither. Make it a block by surrounding it with braces.

.ifPresent(a -> {throw new IllegalArgumentException(); } );

And for your next question, compare your string values with .equals, not with ==.

edited Apr 26 '16 at 15:11

answered Apr 26 '16 at 15:10

rgettman

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Jean Logeart · Answer 2 · 2016-04-26T18:14:41.553

4

Alternate cleaner solution, using anyMatch:

boolean found = map.values()
                   .stream()
                   .anyMatch(a -> stringToBeMatched.equals(a.getField()));
if(found) {
   throw new IllegalArgumentException();
}

edited Apr 26 '16 at 18:14

answered Apr 26 '16 at 15:12

Jean Logeart

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If you're going to write additional code outside the loop, why not just make a function that raises the exception? – EndermanAPM Feb 07 '19 at 02:26

score 2 · Answer 3 · answered Apr 13 '21 at 08:33

2

findAny return a Optional, you can use orElseThrow

map.values()
   .stream()
   .filter(a -> stringToBeMatched == a.getField())
   .findAny()
   .orElseThrow(() -> new IllegalArgumentException());

answered Apr 13 '21 at 08:33

lozanoco

37
1

7

The OP wanted to throw an Exception, if a match is found: Your solution throws an Exception, when no match is found. – Mario Varchmin Apr 13 '21 at 09:19

Java 8 Map: filter value and throw exception if match found

3 Answers3