collections – Page 63

Kotlin’s List missing “add”, “remove”, Map missing “put”, etc?

October 8, 2022 by Tarik

Unlike many languages, Kotlin distinguishes between mutable and immutable collections (lists, sets, maps, etc). Precise control over exactly when collections can be edited is useful for eliminating bugs, and for designing good APIs. https://kotlinlang.org/docs/reference/collections.html You’ll need to use a MutableList list. class TempClass { var myList: MutableList<Int> = mutableListOf<Int>() fun doSomething() { // myList = … Read more

MongoDB Show all contents from all collections

October 8, 2022 by Tarik

Once you are in terminal/command line, access the database/collection you want to use as follows: show dbs use <db name> show collections choose your collection and type the following to see all contents of that collection: db.collectionName.find() More info here on the MongoDB Quick Reference Guide.

Check a collection size with JSTL

October 8, 2022 by Tarik

<c:if test=”${companies.size() > 0}”> </c:if> This syntax works only in EL 2.2 or newer (Servlet 3.0 / JSP 2.2 or newer). If you’re facing a XML parsing error because you’re using JSPX or Facelets instead of JSP, then use gt instead of >. <c:if test=”${companies.size() gt 0}”> </c:if> If you’re actually facing an EL parsing … Read more

Why doesn’t java.util.Set have get(int index)?

October 7, 2022 by Tarik

Because sets have no ordering. Some implementations do (particularly those implementing the java.util.SortedSet interface), but that is not a general property of sets. If you’re trying to use sets this way, you should consider using a list instead.

What is the best way to clone/deep copy a .NET generic Dictionary?

October 6, 2022 by Tarik

(Note: although the cloning version is potentially useful, for a simple shallow copy the constructor I mention in the other post is a better option.) How deep do you want the copy to be, and what version of .NET are you using? I suspect that a LINQ call to ToDictionary, specifying both the key and … Read more

Dictionary returning a default value if the key does not exist [duplicate]

October 5, 2022 by Tarik

TryGetValue will already assign the default value for the type to the dictionary, so you can just use: dictionary.TryGetValue(key, out value); and just ignore the return value. However, that really will just return default(TValue), not some custom default value (nor, more usefully, the result of executing a delegate). There’s nothing more powerful built into the … Read more

How do I overload the square-bracket operator in C#?

October 4, 2022 by Tarik

you can find how to do it here. In short it is: public object this[int i] { get { return InnerList[i]; } set { InnerList[i] = value; } } If you only need a getter the syntax in answer below can be used as well (starting from C# 6).

Iterating through a list in reverse order in java

October 4, 2022 by Tarik

Try this: // Substitute appropriate type. ArrayList<…> a = new ArrayList<…>(); // Add elements to list. // Generate an iterator. Start just after the last element. ListIterator li = a.listIterator(a.size()); // Iterate in reverse. while(li.hasPrevious()) { System.out.println(li.previous()); }

Does List guarantee insertion order?

October 4, 2022 by Tarik

The List<> class does guarantee ordering – things will be retained in the list in the order you add them, including duplicates, unless you explicitly sort the list. According to MSDN: …List “Represents a strongly typed list of objects that can be accessed by index.” The index values must remain reliable for this to be … Read more