I have a list with some identifiers like this: List<long> docIds = new List<long>() { 6, 1, 4, 7, 2 }; Morover, I have another list of <T> items, which are represented by the ids described above. List<T> docs = GetDocsFromDb(…) I need to keep the same order in both collections, so that the items … Read more
I’m new to Java and very confused. I have a large dataset of length 4 int[] and I want to count the number of times that each particular combination of 4 integers occurs. This is very similar to counting word frequencies in a document. I want to create a Map<int[], double> that maps each int[] … Read more
I have a method that returns an IEnumerable<KeyValuePair<string, ArrayList>>, but some of the callers require the result of the method to be a dictionary. How can I convert the IEnumerable<KeyValuePair<string, ArrayList>> into a Dictionary<string, ArrayList> so that I can use TryGetValue? method: public IEnumerable<KeyValuePair<string, ArrayList>> GetComponents() { // … yield return new KeyValuePair<string, ArrayList>(t.Name, controlInformation); … Read more
In Java 8, there is Stream.collect which allows aggregations on collections. In Kotlin, this does not exist in the same way, other than maybe as a collection of extension functions in the stdlib. But it isn’t clear what the equivalences are for different use cases. For example, at the top of the JavaDoc for Collectors … Read more
Is there some one-liner bridge method to dump a given Enumeration to java.util.List or java.util.Set? Something built-in like Arrays.asList() or Collection.toArray() should exist somewhere, but I’m unable to find that in my IntelliJ debugger’s evaluator window (and Google/SO results, too). 7 Answers 7
For example, I am currently doing this: Set<String> setOfTopicAuthors = …. List<String> list = Arrays.asList( setOfTopicAuthors.toArray( new String[0] ) ); Can you beat this ? 6 Answers 6
Here’s a nice pitfall I just encountered. Consider a list of integers: List<Integer> list = new ArrayList<Integer>(); list.add(5); list.add(6); list.add(7); list.add(1); Any educated guess on what happens when you execute list.remove(1)? What about list.remove(new Integer(1))? This can cause some nasty bugs. What is the proper way to differentiate between remove(int index), which removes an element … Read more
How can I loop through a List and grab each item? I want the output to look like this: Console.WriteLine(“amount is {0}, and type is {1}”, myMoney.amount, myMoney.type); Here is my code: static void Main(string[] args) { List<Money> myMoney = new List<Money> { new Money{amount = 10, type = “US”}, new Money{amount = 20, type … Read more
Which is the most efficient way to traverse a collection? List<Integer> a = new ArrayList<Integer>(); for (Integer integer : a) { integer.toString(); } or List<Integer> a = new ArrayList<Integer>(); for (Iterator iterator = a.iterator(); iterator.hasNext();) { Integer integer = (Integer) iterator.next(); integer.toString(); } Please note, that this is not an exact duplicate of this, this, … Read more
I have a List<String> object that contains country names. How can I sort this list alphabetically? 15 Answers 15
