Since Java 7, to instantiate a single-element, immutable Set, you can use: Collections.singleton(thing); Returns an immutable set containing only the specified object. The returned set is serializable. — Javadoc reference: Collections.singleton(T) In Java 8 you can instantiate a Set containing any number of your objects with the following, which is an adaptation of this answer: … Read more
Collection<T>: Provides the base class for a generic collection. List<T>: Represents a strongly typed list of objects that can be accessed by index. Provides methods to search, sort, and manipulate lists. So, according the docs, one is intended as a base class for collections. The other is intended for use as a container. So use … Read more
It doesn’t decrease this automatically. From the doc. public void trimToSize() Trims the capacity of this ArrayList instance to be the list’s current size. An application can use this operation to minimize the storage of an ArrayList instance.
I would implement a data structure with these two dictionaries Dictionary<TKey1, KeyValuePair<TKey2, TValue>> dict1; Dictionary<TKey2, KeyValuePair<TKey1, TValue>> dict2; That way if you are given 1 key you have both the value and the other key as well for easy deletes and updates.
There is no standard small implementation of Map in Java. HashMap is one of the best and most flexible Map implementations around, and is hard to beat. However, in the very small requirement area — where heap usage and speed of construction is paramount — it is possible to do better. I have implemented SmallCollections … Read more
Varargs methods create an array. public static void foo(Object… args) { System.out.println(args.length); } This works, because of the implicit array creation. EnumSet is a class designed to be very, very fast, so by creating all the extra overloads they can skip the array creation step in the first few cases. This is especially true since … Read more
groupBy as defined on TraversableLike produces an immutable.Map, so you can’t make this method produce something else. The order of the elements in each entry is already preserved, but not the order of the keys. The keys are the result of the function supplied, so they don’t really have an order. If you wanted to … Read more
What would you expect a get() method on a Set to do? Sets are not indexed, so a get(int index) makes no sense. (Use a List if you want to get elements by index). get(Object obj) would also not make sense, because you’d have the object that you’re trying to get already. There is already … Read more
The way to add custom config (if you require more than just simple types) is to use a ConfigurationSection, within that for the schema you defined you need a ConfigurationElementCollection (set as default collection with no name), which contains a ConfigurationElement, as follows: public class UserElement : ConfigurationElement { [ConfigurationProperty( “firstName”, IsRequired = true )] … Read more
You could use LINQ: Assert.That(people.Any(p => p.Name == “joe”)); or, if you want to be explicit about there being exactly one person with each name: Assert.That(people.Count(p => p.Name == “joe”), Is.EqualTo(1)); If you want a better error message than “Assertion failed, expected true, was false”, you could create your own assert method. For several collection-related … Read more