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8199318: add idempotent copy operation for Map.Entry

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Reviewed-by: alanb, psandoz, dfuchs
This commit is contained in:
Stuart Marks 2021-06-04 17:13:05 +00:00
parent b27599b3ec
commit cd0678fcf6
3 changed files with 139 additions and 21 deletions
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31
src/java.base/share/classes/java/util/AbstractMap.java
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@ -592,8 +592,11 @@ public abstract class AbstractMap<K,V> implements Map<K,V> {
/**
* An Entry maintaining a key and a value. The value may be
* changed using the {@code setValue} method. This class
* facilitates the process of building custom map
* changed using the {@code setValue} method. Instances of
* this class are not associated with any map's entry-set view.
*
* @apiNote
* This class facilitates the process of building custom map
* implementations. For example, it may be convenient to return
* arrays of {@code SimpleEntry} instances in method
* {@code Map.entrySet().toArray}.
@ -725,10 +728,21 @@ public abstract class AbstractMap<K,V> implements Map<K,V> {
}
/**
* An Entry maintaining an immutable key and value. This class
* does not support method {@code setValue}. This class may be
* convenient in methods that return thread-safe snapshots of
* key-value mappings.
* An unmodifiable Entry maintaining a key and a value. This class
* does not support the {@code setValue} method. Instances of
* this class are not associated with any map's entry-set view.
*
* @apiNote
* Instances of this class are not necessarily immutable, as the key
* and value may be mutable. An instance of <i>this specific class</i>
* is unmodifiable, because the key and value references cannot be
* changed. A reference of this <i>type</i> may not be unmodifiable,
* as a subclass may be modifiable or may provide the appearance of modifiability.
* <p>
* This class may be convenient in methods that return thread-safe snapshots of
* key-value mappings. For alternatives, see the
* {@link Map#entry Map::entry} and {@link Map.Entry#copyOf Map.Entry::copyOf}
* methods.
*
* @since 1.6
*/
@ -788,7 +802,10 @@ public abstract class AbstractMap<K,V> implements Map<K,V> {
* Replaces the value corresponding to this entry with the specified
* value (optional operation). This implementation simply throws
* {@code UnsupportedOperationException}, as this class implements
* an <i>immutable</i> map entry.
* an unmodifiable map entry.
*
* @implSpec
* The implementation in this class always throws {@code UnsupportedOperationException}.
*
* @param value new value to be stored in this entry
* @return (Does not return)