Feature suggestion: Provide efficient way for nullable value lookup in Map

Brian Goetz brian.goetz at oracle.com
Tue Jan 8 15:57:53 UTC 2019

Here's a default implementation that returns the actual key:

    default Optional<Map.Entry<K,V>> getEntry(K key) {
        for (Map.Entry<K,V> e : entrySet) {
            if (Objects.equals(key, e.getKey())
                return Optional.of(e);
        return Optional.empty();

On 1/8/2019 10:50 AM, 
some-java-user-99206970363698485155 at vodafonemail.de wrote:
> Yes it is now possible to implement the methods `getKey(Object key)` and `getEntry(Object key)`
> requested by JDK-6552529 as default methods, however both would have to include that
> "The default implementation returns the provided key. Overriding implementations may return the
> actual key used by the map."
> In this case it is questionable how useful the methods actually are, e.g.
>    Two key objects k1 and k2 with `k1.equals(k2)`
>    Two objects m1 and m2 of different map implementations both containing k1.
>    Then the following is possible:
>    m1.getKey(k2) == k2 // true
>    m2.getKey(k2) == k2 // false
>> Brian Goetz <brian.goetz at oracle.com> hat am 7. Januar 2019 um 00:54 geschrieben:
>> FYI, the comment about compatibility was obsoleted by the addition of
>> default methods in Java 8.

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