Use filter: scala> val collection = List(1,2,3,4,5) collection: List[Int] = List(1, 2, 3, 4, 5) // take only that values that both are even and greater than 3 scala> collection.filter(x => (x % 2 == 0) && (x > 3)) res1: List[Int] = List(4) // you can return this in order to check that there … Read more
Fortunately, you can do this using Java 8 – Streams Assume you have an entity named YourEntity public class YourEntity { private String field1; private String field2; public YourEntity(String field1, String field2) { this.field1 = field1; this.field2 = field2; } public void setField1(String field1) { this.field1 = field1; } public void setField2(String field2) { this.field2 … Read more
There’s already a predicate in Predicates that will help you here — Predicates.notNull() — and you can use Iterables.filter() and the fact that Lists.newArrayList() can take an Iterable to clean this up a little more. Collection<String> resourceIds = Lists.newArrayList( Iterables.filter( Iterables.transform(matchingComputers, yourFunction), Predicates.notNull() ) ); If you don’t actually need a Collection, just an Iterable, … Read more
The short answer is – that’s a limitation of the type inference in Java’s generic system. It can infer generic types against concrete variables, but not against method parameters. I suspect this is because methods are dispatched dynamically depending on the runtime class of the owning object, so at compile time (when all generic information … Read more
Collection is a base interface for most collection classes, whereas Collections is a utility class. I recommend you read the documentation.
If you don’t need sorting, you shouldn’t use a class that does sorting because that means your application will be doing more work than it needs to. (It will make your app faster, in other words).
Scala collections are clever things… Internals of the collection library is one of the more advanced topics in the land of Scala. It involves higher-kinded types, inference, variance, implicits, and the CanBuildFrom mechanism – all to make it incredibly generic, easy to use, and powerful from a user-facing perspective. Understanding it from the point-of-view of … Read more
You start by finding which elements are not already in the collection: var newItems = DownloadedItems.Where(x => !CurrentCollection.Any(y => x.bar == y.bar)); And then just add them: foreach(var item in newItems) { CurrentCollection.Add(item); } Note that the first operation may have quadratic complexity if the size of DownloadedItems is close to the size of CurrentCollection. … Read more
HashSet is Implemented using a hash table. Elements are not ordered. The add, remove, and contains methods have constant time complexity O(1). TreeSet is implemented using a tree structure(red-black tree in algorithm book). The elements in a set are sorted, but the add, remove, and contains methods has time complexity O(log (n)). It offers several … Read more
As of the ides of March 2012, this works in 2.10+: def doMatch(seq: Seq[Int]): Unit = seq match { case last +: Seq() => println(“Final element.”) case head +: tail => println(“Recursing…”); doMatch(tail) } //> doMatch: (seq: Seq[Int])Unit doMatch(List(1, 2)) //> Recursing… //| Final element. More generally, two different head/tail and init/last decomposition objects mirroring … Read more