Filter HashMap using Java 8 lambda

Asked Oct 23 '15 at 21:57

Active Oct 23 '15 at 22:04

Viewed 49 times

I am trying to keep all entries in the Map where the key is in the list of Strings. This is what I have:

List<String> outputKeys = Arrays.asList("key1", "key2", "key3");
foo = map.entrySet()
         .stream()
         .filter(p -> outputKeys.contains(p.getKey()))
         .collect(Collectors.toMap(p -> p.getKey(), p -> p.getValue()));

There are compilation errors at p.getKey() and p.getValue():

Error:(151, 75) java: cannot find symbol
symbol:   method getKey()
location: variable p of type java.lang.Object

edited Oct 23 '15 at 22:04

asked Oct 23 '15 at 21:57

WoLfPwNeR

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How is `map` declared? – Paul Boddington Oct 23 '15 at 22:00
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... and how is `foo` declared? – rgettman Oct 23 '15 at 22:01
`Map map;` and `Map foo = null;` – WoLfPwNeR Oct 23 '15 at 22:03
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And what is the compilation error? – JB Nizet Oct 23 '15 at 22:03
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I think it needs to be `Map map;`, – Paul Boddington Oct 23 '15 at 22:04
@Paul You are right! thanks! – WoLfPwNeR Oct 23 '15 at 22:07
1

Here is my answer (I can't post it any more). If you use the raw type `Map` (rather than `Map`), **all** type information for `map` is ignored. Therefore the method `entrySet` is treated as if it returns a raw `Set`, not a `Set>`. This means (bizarrely) that the methods `getKey` and `getValue` cannot be resolved. If you declare `map` to be of type `Map` the problem disappears. – Paul Boddington Oct 23 '15 at 22:11

Filter HashMap using Java 8 lambda

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