The three forms of looping are nearly identical. The enhanced for loop: for (E element : list) { . . . } is, according to the Java Language Specification, identical in effect to the explicit use of an iterator with a traditional for loop. In the third case, you can only modify the list contents … Read more
if no such option exists, then maybe there is a nice idiomatic one-liner for doing that ? like, using for…of, or similar ? Indeed, there are several ways to convert a Set to an Array: Using Array.from: Note: safer for TypeScript. const array = Array.from(mySet); Simply spreading the Set out in an array: Note: Spreading … Read more
With streams added in Java 8 we can write code like: int[] example1 = list.stream().mapToInt(i->i).toArray(); // OR int[] example2 = list.stream().mapToInt(Integer::intValue).toArray(); Thought process: The simple Stream#toArray returns an Object[] array, so it is not what we want. Also, Stream#toArray(IntFunction<A[]> generator) doesn’t do what we want, because the generic type A can’t represent the primitive type … Read more
Set<Foo> foo = new HashSet<Foo>(myList);
Java 8 (2014) solves this problem using streams and lambdas in one line of code: List<Person> beerDrinkers = persons.stream() .filter(p -> p.getAge() > 16).collect(Collectors.toList()); Here’s a tutorial. Use Collection#removeIf to modify the collection in place. (Notice: In this case, the predicate will remove objects who satisfy the predicate): persons.removeIf(p -> p.getAge() <= 16); lambdaj allows … Read more
You can use flatMap to flatten the internal lists (after converting them to Streams) into a single Stream, and then collect the result into a list: List<List<Object>> list = … List<Object> flat = list.stream() .flatMap(List::stream) .collect(Collectors.toList());
List<Value> list = new ArrayList<Value>(map.values()); assuming: Map<Key,Value> map;
Like this: Set<T> mySet = new HashSet<>(Arrays.asList(someArray)); In Java 9+, if unmodifiable set is ok: Set<T> mySet = Set.of(someArray); In Java 10+, the generic type parameter can be inferred from the arrays component type: var mySet = Set.of(someArray); Be careful Set.of throws IllegalArgumentException – if there are any duplicate elements in someArray. See more details: … Read more
There is a shorthand that I use that is not very time efficient, but fits on a single line: Set<String> h = new HashSet<>(Arrays.asList(“a”, “b”)); Again, this is not time efficient since you are constructing an array, converting to a list and using that list to create a set. When initializing static final sets I … Read more
List myList = new ArrayList(); or with generics (Java 7 or later) List<MyType> myList = new ArrayList<>(); or with generics (Old java versions) List<MyType> myList = new ArrayList<MyType>();