I just faced the same issue and decided to map my key to an Entry. This allows for the same indexing features provided by a map while having more than one property associated with a key. I think it’s a much neater solution that creating a separate class or nesting maps. Map<String, Entry<Action, Boolean>> actionMap … Read more
Problem is that by definition putIfAbsent return old value and not new value (old value for absent is always null). Use computeIfAbsent – this will return new value for you. private static String get(final String key) { return map.computeIfAbsent(key, s -> “value 3”); }
You don’t need to re-add the ArrayList back to your Map. If the ArrayList already exists then just add your value to it. An improved implementation might look like: Map<String, Collection<String>> map = new HashMap<String, Collection<String>>(); while processing each line: String user = user field from line String value = value field from line Collection<String> … Read more
Rules. Kids know rules. Kids know that certain items belong in certain places. A HashMap is like a set of rules that say, given an item (your shoes, your favorite book, or your clothes) that there is a specific place that they should go (the shoe rack, the bookshelf, or the closet). So if you … Read more
The Javadoc makes a pretty good argument: Enum maps are represented internally as arrays. This representation is extremely compact and efficient. Implementation note: All basic operations execute in constant time. They are likely (though not guaranteed) to be faster than their HashMap counterparts.
Do you mean something like this? scala> val m = collection.immutable.HashMap(0 -> 1, 2 -> 3) m: scala.collection.immutable.HashMap[Int,Int] = Map((0,1), (2,3)) scala> m.get(0) res0: Option[Int] = Some(1) scala> m.get(2) res1: Option[Int] = Some(3) scala> m.get(1) res2: Option[Int] = None
Check Ick’s maybe. You don’t need to significantly refactor your code, just intersperse maybe proxies when necessary: params[:subject].maybe[:name] The same author (raganwald) also wrote andand, with the same idea.
A switch construct is faster (or at least not slower). That’s mostly because a switch construct gives static data to the compiler, while a runtime structure like a hash map doesn’t. When possible compilers should compile switch constructs into array of code pointers: each item of the array (indexed by your indexes) points to the … Read more
You aren’t going to be able to do this from the HashMap class alone. I would take the Map<String, String> codes, construct a reverse map of TreeMap<String, String> reversedMap where you map the values of the codes Map to the keys (this would require your original Map to have a one-to-one mapping from key-to-value). Since … Read more
HashMap<String, String> x; Random random = new Random(); List<String> keys = new ArrayList<String>(x.keySet()); String randomKey = keys.get( random.nextInt(keys.size()) ); String value = x.get(randomKey);