The main difference is that Collections.emptyList() returns an immutable list, i.e., a list to which you cannot add elements. (Same applies to the List.of() introduced in Java 9.) In the rare cases where you do want to modify the returned list, Collections.emptyList() and List.of() are thus not a good choices. I’d say that returning an … Read more
System.Collections.Generic.Dictionary<TKey, TValue> and System.Collections.Hashtable classes both maintain a hash table data structure internally. None of them guarantee preserving the order of items. Leaving boxing/unboxing issues aside, most of the time, they should have very similar performance. The primary structural difference between them is that Dictionary relies on chaining (maintaining a list of items for each … Read more
If you use the Apache Commons Collections library in your project, you may use the CollectionUtils.isEmpty and MapUtils.isEmpty() methods which respectively check if a collection or a map is empty or null (i.e. they are “null-safe”). The code behind these methods is more or less what user @icza has written in his answer. Regardless of … Read more
Simply casting to List<TestB> almost works; but it doesn’t work because you can’t cast a generic type of one parameter to another. However, you can cast through an intermediate wildcard type and it will be allowed (since you can cast to and from wildcard types, just with an unchecked warning): List<TestB> variable = (List<TestB>)(List<?>) collectionOfListA;
Let me give a few examples with some alternatives to avoid a ConcurrentModificationException. Suppose we have the following collection of books List<Book> books = new ArrayList<Book>(); books.add(new Book(new ISBN(“0-201-63361-2”))); books.add(new Book(new ISBN(“0-201-63361-3”))); books.add(new Book(new ISBN(“0-201-63361-4”))); Collect and Remove The first technique consists in collecting all the objects that we want to delete (e.g. using an … Read more
You will need to iterate on the items, and clone them one by one, putting the clones in your result array as you go. public static List<Dog> cloneList(List<Dog> list) { List<Dog> clone = new ArrayList<Dog>(list.size()); for (Dog item : list) clone.add(item.clone()); return clone; } For that to work, obviously, you will have to get your … Read more
If you care about order, then just use the equals method: list1.equals(list2) From the javadoc: Compares the specified object with this list for equality. Returns true if and only if the specified object is also a list, both lists have the same size, and all corresponding pairs of elements in the two lists are equal. … Read more
As stated, if you want to get 4 as the result, you can do like this: var nonintersect = array2.Except(array1); If you want the real non-intersection (also both 1 and 4), then this should do the trick: var nonintersect = array1.Except(array2).Union( array2.Except(array1)); This will not be the most performant solution, but for small lists it … Read more
For simple cases such as the one illustrated, they are mostly the same. However, there are a number of subtle differences that might be significant. One issue is with ordering. With Stream.forEach, the order is undefined. It’s unlikely to occur with sequential streams, still, it’s within the specification for Stream.forEach to execute in some arbitrary … Read more
List list = new ArrayList(coll); Collections.sort(list); As Erel Segal Halevi says below, if coll is already a list, you can skip step one. But that would depend on the internals of TreeBidiMap. List list; if (coll instanceof List) list = (List)coll; else list = new ArrayList(coll);