TreeSet is sorted by element order; LinkedHashSet retains insertion order. Hopefully one of those is what you were after. You’ve specified that you want to be able to insert at an arbitrary location, I suspect you’ll have to write your own – just create a class containing a HashSet<T> and an ArrayList<T>; when adding an … Read more
The List is index based and new items will always be added to the end of the list. You can insert items at a certain index so the next items will move one position. So yes, you can use it safely that way… The List(T) class is the generic equivalent of the ArrayList class. It … Read more
TL;DR List<V> al = new ArrayList<V>(hashMapVar.values()); Explanation Because HashMap#values() returns a java.util.Collection<V> and you can’t cast a Collection into an ArrayList, thus you get ClassCastException. I’d suggest using ArrayList(Collection<? extends V>) constructor. This constructor accepts an object which implements Collection<? extends V> as an argument. You won’t get ClassCastException when you pass the result of … Read more
Yeah. Queue LinkedList being the most trivial concrete implementation.
using System; using System.Collections.Generic; using System.Linq; class C { public static void Main() { var a = new []{ “First”, “Second”, “Third” }; System.Console.Write(string.Join(“,”, a)); } }
You can’t remove from list if you’re browsing it with “for each” loop. You can use Iterator. Replace: for (DrugStrength aDrugStrength : aDrugStrengthList) { if (!aDrugStrength.isValidDrugDescription()) { aDrugStrengthList.remove(aDrugStrength); } } With: for (Iterator<DrugStrength> it = aDrugStrengthList.iterator(); it.hasNext(); ) { DrugStrength aDrugStrength = it.next(); if (!aDrugStrength.isValidDrugDescription()) { it.remove(); } }
ArrayDeque is best. See this benchmark, which comes from this blog post about the results of benchmarking this. ArrayDeque doesn’t have the overhead of node allocations that LinkedList does nor the overhead of shifting the array contents left on remove that ArrayList has. In the benchmark, it performs about 3x as well as LinkedList for … Read more
[*] I like @b4hand’s examples, and indeed I have used in the past ChainMap-like structures (but not ChainMap itself) for the two purposes he mentions: multi-layered configuration overrides, and variable stack/scope emulation. I’d like to point out two other motivations/advantages/differences of ChainMap, compared to using a dict-update loop, thus only storing the “final” version”: More … Read more
Been a while since this question was asked but these days I’m partial to something like: public static <K, V> Map<K, V> zipToMap(List<K> keys, List<V> values) { return IntStream.range(0, keys.size()).boxed() .collect(Collectors.toMap(keys::get, values::get)); } For those unfamiliar with streams, what this does is gets an IntStream from 0 to the length, then boxes it, making it … Read more
You should absolutely use isEmpty(). Computing the size() of an arbitrary list could be expensive. Even validating whether it has any elements can be expensive, of course, but there’s no optimization for size() which can’t also make isEmpty() faster, whereas the reverse is not the case. For example, suppose you had a linked list structure … Read more