The most common case where using entrySet is preferable over keySet is when you are iterating through all of the key/value pairs in a Map. This is more efficient: for (Map.Entry entry : map.entrySet()) { Object key = entry.getKey(); Object value = entry.getValue(); } than: for (Object key : map.keySet()) { Object value = map.get(key); … Read more
You could consider doing the filtering task on a background thread which would invoke a callback method when it’s done, or simply restart filtering if input is changed. The general idea is to be able to use it like this: public partial class YourForm : Form { private readonly BackgroundWordFilter _filter; public YourForm() { InitializeComponent(); … Read more
I am the original author of the patch which appeared in 7u6, CR#7118743 : Alternative Hashing for String with Hash-based Maps. I’ll acknowledge right up front that the initialization of hashSeed is a bottleneck but it is not one we expected to be a problem since it only happens once per Hash Map instance. For … Read more
Arrays.asList() would do the trick here. String[] words = {“ace”, “boom”, “crew”, “dog”, “eon”}; List<String> wordList = Arrays.asList(words); For converting to Set, you can do as below Set<T> mySet = new HashSet<T>(Arrays.asList(words));
Collections.newSetFromMap Set<Object> weakHashSet = Collections.newSetFromMap( new WeakHashMap<Object, Boolean>() ); As seen in Collections.newSetFromMap documentation, passing a WeakHashMap to get a Set.
I was really surprised to find this topic to be so old and yet no one has yet provided any tests regarding the case. Using ScalaMeter I have created tests of add, get and remove for both HashMap and ConcurrentHashMap in two scenarios: using single thread using as many threads as I have cores available. … Read more
what will be faster, to call Clear() method or creating a `new List()? This is impossible to answer. It really depends on a lot of factors, including how long the collection has existed. The best option here would be to: Profile the application, and see if this really matters. It likely won’t make any perceptible … Read more
As stated on this link: CopyOnWriteArrayList is a concurrent Collection class introduced in Java 5 Concurrency API along with its popular cousin ConcurrentHashMap in Java. CopyOnWriteArrayList implements List interface like ArrayList, Vector and LinkedList but its a thread-safe collection and it achieves its thread-safety in a slightly different way than Vector or other thread-safe collection … Read more
HashSet consumes about 5.5 times more memory than ArrayList for the same number of elements (although they’re both still linear), and has significantly slower iteration (albeit with the same asymptotics); a quick Google search suggests a 2-3x slowdown for HashSet iteration versus ArrayList. If you don’t care about uniqueness or the performance of contains, then … Read more
The whole point is that reified generics have support in the compiler for preserving type information, whereas type erased generics don’t. AFAIK, the whole point of having type erasure in the first place was to enable backwards compatibility (e.g. lower versioned JVMs could still understand generic classes). You can explicitly add the type information in … Read more