Yes, Blah.valueOf("A")
will give you Blah.A
.
Note that the name must be an exact match, including case: Blah.valueOf("a")
and Blah.valueOf("A ")
both throw an IllegalArgumentException
.
The static methods valueOf()
and values()
are created at compile time and do not appear in source code. They do appear in Javadoc, though; for example, Dialog.ModalityType
shows both methods.
If your data structure has many-to-one mapping between keys and values you should iterate over entries and pick all suitable keys:
public static <T, E> Set<T> getKeysByValue(Map<T, E> map, E value) {
Set<T> keys = new HashSet<T>();
for (Entry<T, E> entry : map.entrySet()) {
if (Objects.equals(value, entry.getValue())) {
keys.add(entry.getKey());
}
}
return keys;
}
In case of one-to-one relationship, you can return the first matched key:
public static <T, E> T getKeyByValue(Map<T, E> map, E value) {
for (Entry<T, E> entry : map.entrySet()) {
if (Objects.equals(value, entry.getValue())) {
return entry.getKey();
}
}
return null;
}
In Java 8:
public static <T, E> Set<T> getKeysByValue(Map<T, E> map, E value) {
return map.entrySet()
.stream()
.filter(entry -> Objects.equals(entry.getValue(), value))
.map(Map.Entry::getKey)
.collect(Collectors.toSet());
}
Also, for Guava users, BiMap may be useful. For example:
BiMap<Token, Character> tokenToChar =
ImmutableBiMap.of(Token.LEFT_BRACKET, '[', Token.LEFT_PARENTHESIS, '(');
Token token = tokenToChar.inverse().get('(');
Character c = tokenToChar.get(token);
Best Answer
Jeremy Manson, the god when it comes to the Java Memory Model, has a three part blog on this topic - because in essence you are asking the question "Is it safe to access an immutable HashMap" - the answer to that is yes. But you must answer the predicate to that question which is - "Is my HashMap immutable". The answer might surprise you - Java has a relatively complicated set of rules to determine immutability.
For more info on the topic, read Jeremy's blog posts:
Part 1 on Immutability in Java: http://jeremymanson.blogspot.com/2008/04/immutability-in-java.html
Part 2 on Immutability in Java: http://jeremymanson.blogspot.com/2008/07/immutability-in-java-part-2.html
Part 3 on Immutability in Java: http://jeremymanson.blogspot.com/2008/07/immutability-in-java-part-3.html