The book Java Generics and Collections has this information (pages: 188, 211, 222, 240). List implementations: get add contains next remove(0) iterator.remove ArrayList O(1) O(1) O(n) O(1) O(n) O(n) LinkedList O(n) O(1) O(n) O(1) O(1) O(1) CopyOnWrite-ArrayList O(1) O(n) O(n) O(1) O(n) O(n) Set implementations: add contains next notes HashSet O(1) O(1) O(h/n) h is … Read more
Enumerable.SequenceEqual Determines whether two sequences are equal by comparing their elements by using a specified IEqualityComparer(T). You can’t directly compare the list & the dictionary, but you could compare the list of values from the Dictionary with the list
Sure you could write that: public static class Utils { public static bool IsAny<T>(this IEnumerable<T> data) { return data != null && data.Any(); } } however, be cautious that not all sequences are repeatable; generally I prefer to only walk them once, just in case.
First off: a List is a Collection. It is a specialized Collection, however. A Collection is just that: a collection of items. You can add stuff, remove stuff, iterate over stuff and query how much stuff is in there. A List adds the information about a defined sequence of stuff to it: You can get … Read more
Using linq: YourList.OrderBy(x => rnd.Next()).Take(5)
For junit4! This question deserves a new answer written for junit5. I realise this answer is written a couple years after the question, probably this feature wasn’t around then. But now, it’s easy to just do this: @Test public void test_array_pass() { List<String> actual = Arrays.asList(“fee”, “fi”, “foe”); List<String> expected = Arrays.asList(“fee”, “fi”, “foe”); assertThat(actual, … Read more
This seemed related, but I didn’t understand it properly: c# Dictionary: making the Key case-insensitive through declarations It is indeed related. The solution is to tell the dictionary instance not to use the standard string compare method (which is case sensitive) but rather to use a case insensitive one. This is done using the appropriate … Read more
Length() tends to refer to contiguous elements – a string has a length for example. Count() tends to refer to the number of elements in a looser collection. Size() tends to refer to the size of the collection, often this can be different from the length in cases like vectors (or strings), there may be … Read more
HashSet is a set, e.g. {1,2,3,4,5} HashMap is a key -> value (key to value) map, e.g. {a -> 1, b -> 2, c -> 2, d -> 1} Notice in my example above that in the HashMap there must not be duplicate keys, but it may have duplicate values. In the HashSet, there must … Read more
An unmodifiable collection is often a wrapper around a modifiable collection which other code may still have access to. So while you can’t make any changes to it if you only have a reference to the unmodifiable collection, you can’t rely on the contents not changing. An immutable collection guarantees that nothing can change the … Read more