Java : ConcurrentSkipListSet with Examples

void test(Set<String> set) throws InterruptedException {
    set.add("a");
    set.add("b");
    set.add("c");
    set.add("d");
    set.add("e");

    try (final var executor = Executors.newSingleThreadScheduledExecutor()) {

        executor.schedule(() -> {
            System.out.println("-- add value! --");
            set.add("x");
        }, 5, TimeUnit.SECONDS);

        try {
            for (final var value : set) {
                System.out.println("value = " + value);
                TimeUnit.SECONDS.sleep(2);
            }
        } catch (ConcurrentModificationException e) {
            System.out.println("ConcurrentModificationException!");
        }
    }

    System.out.println("-- end --");
    System.out.println("set = " + set);
}

test(new TreeSet<>());

// Result
// ↓
//value = a
//value = b
//value = c
//-- add value! --
//ConcurrentModificationException!
//-- end --
//set = [a, b, c, d, e, x]

test(new ConcurrentSkipListSet<>());

// Result
// ↓
//value = a
//value = b
//value = c
//-- add value! --
//value = d
//value = e
//value = x
//-- end --
//set = [a, b, c, d, e, x]

final var navigableSet = new ConcurrentSkipListSet<String>();
navigableSet.add("ccc");
navigableSet.add("ddd");
navigableSet.add("aaa");
navigableSet.add("bbb");

System.out.println(navigableSet); // [aaa, bbb, ccc, ddd]

final var hashSet = ConcurrentHashMap.<String>newKeySet();
hashSet.add("ccc");
hashSet.add("ddd");
hashSet.add("aaa");
hashSet.add("bbb");

System.out.println(hashSet); // [aaa, ccc, bbb, ddd]

ConcurrentSkipListSet ()

Constructs a new, empty set that orders its elements according to their natural ordering.

final var set = new ConcurrentSkipListSet<String>();
System.out.println(set); // []
System.out.println(set.isEmpty()); // true

set.add("b");
set.add("a");
set.add("c");

System.out.println(set); // [a, b, c]
System.out.println(set.size()); // 3

final var set = new ConcurrentSkipListSet<Integer>();

set.add(100);
set.add(999);
set.add(-200);

System.out.println(set); // [-200, 100, 999]

ConcurrentSkipListSet (Collection<? extends E> c)

Constructs a new set containing the elements in the specified collection, that orders its elements according to their natural ordering.

final var c = List.of("b", "a", "c");

final var set = new ConcurrentSkipListSet<>(c);
System.out.println(set); // [a, b, c]
System.out.println(set.size()); // 3

ConcurrentSkipListSet (Comparator<? super E> comparator)

Constructs a new, empty set that orders its elements according to the specified comparator.

final var src = List.of("bbb", "aaa", "ccc");

final var set1 = new ConcurrentSkipListSet<String>();
set1.addAll(src);
System.out.println(set1); // [aaa, bbb, ccc]

final var set2 = new ConcurrentSkipListSet<String>(Comparator.reverseOrder());
set2.addAll(src);
System.out.println(set2); // [ccc, bbb, aaa]

ConcurrentSkipListSet (SortedSet<E> s)

Constructs a new set containing the same elements and using the same ordering as the specified sorted set.

final var s = new ConcurrentSkipListSet<String>(Comparator.reverseOrder());
s.add("a");
s.add("b");
s.add("c");

System.out.println(s); // [c, b, a]

final var set = new ConcurrentSkipListSet<>(s);
System.out.println(set); // [c, b, a]
System.out.println(set.size()); // 3

boolean add (E e)

Adds the specified element to this set if it is not already present.

final var set = new ConcurrentSkipListSet<String>();
System.out.println(set); // []

System.out.println(set.add("a")); // true
System.out.println(set); // [a]

System.out.println(set.add("b")); // true
System.out.println(set); // [a, b]

System.out.println(set.add("c")); // true
System.out.println(set); // [a, b, c]

System.out.println(set.add("a")); // false
System.out.println(set); // [a, b, c]

E ceiling (E e)

Returns the least element in this set greater than or equal to the given element, or null if there is no such element.

final var set = new ConcurrentSkipListSet<String>();
set.add("b");
set.add("d");
set.add("f");

System.out.println(set); // [b, d, f]

System.out.println(set.ceiling("a")); // b
System.out.println(set.ceiling("b")); // b
System.out.println(set.ceiling("c")); // d
System.out.println(set.ceiling("d")); // d
System.out.println(set.ceiling("e")); // f
System.out.println(set.ceiling("f")); // f
System.out.println(set.ceiling("g")); // null

void clear ()

Removes all of the elements from this set.

final var set = new ConcurrentSkipListSet<String>();
System.out.println(set); // []

set.add("a");
System.out.println(set); // [a]

set.add("b");
System.out.println(set); // [a, b]

set.clear();
System.out.println(set); // []

ConcurrentSkipListSet<E> clone ()

Returns a shallow copy of this ConcurrentSkipListSet instance.

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]

final var cloned = set.clone();
System.out.println(cloned); // [a, b, c]
System.out.println(cloned.getClass()); // class java.util.concurrent.ConcurrentSkipListSet

Comparator<? super E> comparator ()

Returns the comparator used to order the elements in this set, or null if this set uses the natural ordering of its elements.

final var set = new ConcurrentSkipListSet<String>();
System.out.println(set); // []

final var comparator = set.comparator();
System.out.println(comparator); // null

final var set = new ConcurrentSkipListSet<String>(Comparator.reverseOrder());
System.out.println(set); // []

final var comparator = set.comparator();
System.out.println(Objects.equals(comparator, Comparator.reverseOrder())); // true

final var set = new ConcurrentSkipListSet<>(String.CASE_INSENSITIVE_ORDER);
System.out.println(set); // []

final var comparator = set.comparator();
System.out.println(Objects.equals(comparator, String.CASE_INSENSITIVE_ORDER)); // true

boolean contains (Object o)

Returns true if this set contains the specified element.

final var set = new ConcurrentSkipListSet<String>();
Collections.addAll(set, "a", "b", "c");
System.out.println(set); // [a, b, c]

System.out.println(set.contains("")); // false
System.out.println(set.contains("a")); // true
System.out.println(set.contains("b")); // true
System.out.println(set.contains("c")); // true

System.out.println(set.contains("X")); // false
System.out.println(set.contains("abc")); // false

Iterator<E> descendingIterator ()

Returns an iterator over the elements in this set in descending order.

final var set = new ConcurrentSkipListSet<String>();
set.add("aaa");
set.add("bbb");
set.add("ccc");

System.out.println(set); // [aaa, bbb, ccc]

final var iterator = set.descendingIterator();

System.out.println("-- forEachRemaining --");
iterator.forEachRemaining(s -> {
    System.out.println(s);
});

// Result
// ↓
//-- forEachRemaining --
//ccc
//bbb
//aaa

NavigableSet<E> descendingSet ()

Returns a reverse order view of the elements contained in this set.

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]

final var descSet = set.descendingSet();
System.out.println(descSet); // [c, b, a]

set.add("d");

System.out.println(set); // [a, b, c, d]
System.out.println(descSet); // [d, c, b, a]

descSet.remove("b");

System.out.println(set); // [a, c, d]
System.out.println(descSet); // [d, c, a]

boolean equals (Object o)

Compares the specified object with this set for equality.

final var set = new ConcurrentSkipListSet<String>();
Collections.addAll(set, "a", "b", "c");
System.out.println(set); // [a, b, c]

System.out.println(set.equals(Set.of("a"))); // false
System.out.println(set.equals(Set.of("a", "b"))); // false
System.out.println(set.equals(Set.of("a", "b", "c"))); // true
System.out.println(set.equals(Set.of("c", "b", "a"))); // true

final var set = new ConcurrentSkipListSet<String>();
Collections.addAll(set, "a", "b", "c");
System.out.println(set); // [a, b, c]

final var hashSet = new HashSet<>(set);
System.out.println(hashSet); // [a, b, c]
System.out.println(set.equals(hashSet)); // true

final var treeSet = new TreeSet<>(set);
System.out.println(treeSet); // [a, b, c]
System.out.println(set.equals(treeSet)); // true

final var list = new ArrayList<>(set);
System.out.println(list); // [a, b, c]
System.out.println(set.equals(list)); // false

E first ()

Returns the first (lowest) element currently in this set.

final var set = new ConcurrentSkipListSet<String>();
System.out.println(set); // []

set.add("b");

System.out.println(set); // [b]
System.out.println(set.first()); // b

set.add("c");

System.out.println(set); // [b, c]
System.out.println(set.first()); // b

set.add("a");

System.out.println(set); // [a, b, c]
System.out.println(set.first()); // a

final var set = new ConcurrentSkipListSet<String>();
System.out.println(set); // []

try {
    set.first();
} catch (NoSuchElementException e) {
    System.out.println("NoSuchElementException!");
}

// Result
// ↓
//NoSuchElementException!

E floor (E e)

Returns the greatest element in this set less than or equal to the given element, or null if there is no such element.

final var set = new ConcurrentSkipListSet<String>();
set.add("b");
set.add("d");
set.add("f");

System.out.println(set); // [b, d, f]

System.out.println(set.floor("a")); // null
System.out.println(set.floor("b")); // b
System.out.println(set.floor("c")); // b
System.out.println(set.floor("d")); // d
System.out.println(set.floor("e")); // d
System.out.println(set.floor("f")); // f
System.out.println(set.floor("g")); // f

NavigableSet<E> headSet (E toElement)

Returns a view of the portion of this set whose elements are strictly less than toElement.

final var set = new ConcurrentSkipListSet<String>();
set.add("x");
set.add("y");
set.add("z");

System.out.println(set); // [x, y, z]

final var headSet = set.headSet("z");
System.out.println(headSet); // [x, y]

set.add("a");

System.out.println(set); // [a, x, y, z]
System.out.println(headSet); // [a, x, y]

headSet.remove("x");

System.out.println(set); // [a, y, z]
System.out.println(headSet); // [a, y]

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]

System.out.println(set.headSet("a")); // []
System.out.println(set.headSet("b")); // [a]
System.out.println(set.headSet("c")); // [a, b]
System.out.println(set.headSet("d")); // [a, b, c]

NavigableSet<E> headSet (E toElement, boolean inclusive)

Returns a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement.

final var set = new ConcurrentSkipListSet<String>();
set.add("x");
set.add("y");
set.add("z");

System.out.println(set); // [x, y, z]

final var headSet = set.headSet("y", true);
System.out.println(headSet); // [x, y]

set.add("a");

System.out.println(set); // [a, x, y, z]
System.out.println(headSet); // [a, x, y]

headSet.remove("x");

System.out.println(set); // [a, y, z]
System.out.println(headSet); // [a, y]

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]

System.out.println(set.headSet("a")); // []
System.out.println(set.headSet("a", true)); // [a]

System.out.println(set.headSet("b")); // [a]
System.out.println(set.headSet("b", true)); // [a, b]

System.out.println(set.headSet("c")); // [a, b]
System.out.println(set.headSet("c", true)); // [a, b, c]

System.out.println(set.headSet("d")); // [a, b, c]
System.out.println(set.headSet("d", true)); // [a, b, c]

E higher (E e)

Returns the least element in this set strictly greater than the given element, or null if there is no such element.

final var set = new ConcurrentSkipListSet<String>();
set.add("b");
set.add("d");
set.add("f");

System.out.println(set); // [b, d, f]

System.out.println(set.higher("a")); // b
System.out.println(set.higher("b")); // d
System.out.println(set.higher("c")); // d
System.out.println(set.higher("d")); // f
System.out.println(set.higher("e")); // f
System.out.println(set.higher("f")); // null
System.out.println(set.higher("g")); // null

boolean isEmpty ()

Returns true if this set contains no elements.

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]
System.out.println(set.isEmpty()); // false

set.clear();
System.out.println(set); // []
System.out.println(set.isEmpty()); // true

Iterator<E> iterator ()

Returns an iterator over the elements in this set in ascending order.

final var set = new ConcurrentSkipListSet<String>();
set.add("aaa");
set.add("bbb");
set.add("ccc");

System.out.println(set); // [aaa, bbb, ccc]

final var iterator = set.iterator();

System.out.println("-- forEachRemaining --");
iterator.forEachRemaining(s -> {
    System.out.println(s);
});

// Result
// ↓
//-- forEachRemaining --
//aaa
//bbb
//ccc

E last ()

Returns the last (highest) element currently in this set.

final var set = new ConcurrentSkipListSet<String>();
System.out.println(set); // []

set.add("b");

System.out.println(set); // [b]
System.out.println(set.last()); // b

set.add("a");

System.out.println(set); // [a, b]
System.out.println(set.last()); // b

set.add("c");

System.out.println(set); // [a, b, c]
System.out.println(set.last()); // c

final var set = new ConcurrentSkipListSet<String>();
System.out.println(set); // []

try {
    set.last();
} catch (NoSuchElementException e) {
    System.out.println("NoSuchElementException!");
}

// Result
// ↓
//NoSuchElementException!

E lower (E e)

Returns the greatest element in this set strictly less than the given element, or null if there is no such element.

final var set = new ConcurrentSkipListSet<String>();
set.add("b");
set.add("d");
set.add("f");

System.out.println(set); // [b, d, f]

System.out.println(set.lower("a")); // null
System.out.println(set.lower("b")); // null
System.out.println(set.lower("c")); // b
System.out.println(set.lower("d")); // b
System.out.println(set.lower("e")); // d
System.out.println(set.lower("f")); // d
System.out.println(set.lower("g")); // f

E pollFirst ()

Retrieves and removes the first (lowest) element, or returns null if this set is empty.

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]

System.out.println(set.pollFirst()); // a
System.out.println(set); // [b, c]

System.out.println(set.pollFirst()); // b
System.out.println(set); // [c]

System.out.println(set.pollFirst()); // c
System.out.println(set); // []

System.out.println(set.pollFirst()); // null

E pollLast ()

Retrieves and removes the last (highest) element, or returns null if this set is empty.

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]

System.out.println(set.pollLast()); // c
System.out.println(set); // [a, b]

System.out.println(set.pollLast()); // b
System.out.println(set); // [a]

System.out.println(set.pollLast()); // a
System.out.println(set); // []

System.out.println(set.pollLast()); // null

boolean remove (Object o)

Removes the specified element from this set if it is present.

final var src = Set.of("a", "b", "c");

{
    final var set = new ConcurrentSkipListSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.remove("")); // false
    System.out.println(set); // [a, b, c]
}
{
    final var set = new ConcurrentSkipListSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.remove("a")); // true
    System.out.println(set); // [b, c]
}
{
    final var set = new ConcurrentSkipListSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.remove("b")); // true
    System.out.println(set); // [a, c]
}
{
    final var set = new ConcurrentSkipListSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.remove("X")); // false
    System.out.println(set); // [a, b, c]
}

boolean removeAll (Collection<?> c)

Removes from this set all of its elements that are contained in the specified collection.

final var src = Set.of("a", "b", "c");

{
    final var set = new ConcurrentSkipListSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of())); // false
    System.out.println(set); // [a, b, c]
}
{
    final var set = new ConcurrentSkipListSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of("a"))); // true
    System.out.println(set); // [b, c]
}
{
    final var set = new ConcurrentSkipListSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of("a", "b"))); // true
    System.out.println(set); // [c]
}
{
    final var set = new ConcurrentSkipListSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of("b", "a"))); // true
    System.out.println(set); // [c]
}
{
    final var set = new ConcurrentSkipListSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of("a", "b", "c"))); // true
    System.out.println(set); // []
}
{
    final var set = new ConcurrentSkipListSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of("X", "Y"))); // false
    System.out.println(set); // [a, b, c]
}
{
    final var set = new ConcurrentSkipListSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of("a", "X"))); // true
    System.out.println(set); // [b, c]
}

int size ()

Returns the number of elements in this set.

final var set1 = new ConcurrentSkipListSet<String>();
System.out.println(set1); // []
System.out.println(set1.size()); // 0

final var set2 = new ConcurrentSkipListSet<String>();
Collections.addAll(set2, "a", "b", "c");
System.out.println(set2); // [a, b, c]
System.out.println(set2.size()); // 3

Spliterator<E> spliterator ()

Returns a Spliterator over the elements in this set.

final var set = new ConcurrentSkipListSet<String>();
set.add("aaa");
set.add("bbb");
set.add("ccc");

System.out.println(set); // [aaa, bbb, ccc]

final var spliterator = set.spliterator();

System.out.println("-- forEachRemaining --");
spliterator.forEachRemaining(s -> {
    System.out.println(s);
});

// Result
// ↓
//-- forEachRemaining --
//aaa
//bbb
//ccc

NavigableSet<E> subSet (E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)

Returns a view of the portion of this set whose elements range from fromElement to toElement.

final var set = new ConcurrentSkipListSet<String>();
set.add("x");
set.add("y");
set.add("z");

System.out.println(set); // [x, y, z]

final var subSet = set.subSet("a", true, "y", true);
System.out.println(subSet); // [x, y]

set.add("a");

System.out.println(set); // [a, x, y, z]
System.out.println(subSet); // [a, x, y]

subSet.remove("x");

System.out.println(set); // [a, y, z]
System.out.println(subSet); // [a, y]

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]

System.out.println(set.subSet("a", true, "c", true)); // [a, b, c]
System.out.println(set.subSet("a", true, "c", false)); // [a, b]
System.out.println(set.subSet("a", false, "c", true)); // [b, c]
System.out.println(set.subSet("a", false, "c", false)); // [b]

System.out.println(set.subSet("a", true, "a", false)); // []
System.out.println(set.subSet("a", true, "b", false)); // [a]
System.out.println(set.subSet("a", true, "c", false)); // [a, b]
System.out.println(set.subSet("a", true, "d", false)); // [a, b, c]

System.out.println(set.subSet("a", true, "d", false)); // [a, b, c]
System.out.println(set.subSet("b", true, "d", false)); // [b, c]
System.out.println(set.subSet("c", true, "d", false)); // [c]
System.out.println(set.subSet("d", true, "d", false)); // []

NavigableSet<E> subSet (E fromElement, E toElement)

Returns a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive.

final var set = new ConcurrentSkipListSet<String>();
set.add("x");
set.add("y");
set.add("z");

System.out.println(set); // [x, y, z]

final var subSet = set.subSet("a", "z");
System.out.println(subSet); // [x, y]

set.add("a");

System.out.println(set); // [a, x, y, z]
System.out.println(subSet); // [a, x, y]

subSet.remove("x");

System.out.println(set); // [a, y, z]
System.out.println(subSet); // [a, y]

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]

System.out.println(set.subSet("a", "a")); // []
System.out.println(set.subSet("a", "b")); // [a]
System.out.println(set.subSet("a", "c")); // [a, b]
System.out.println(set.subSet("a", "d")); // [a, b, c]

System.out.println(set.subSet("a", "d")); // [a, b, c]
System.out.println(set.subSet("b", "d")); // [b, c]
System.out.println(set.subSet("c", "d")); // [c]
System.out.println(set.subSet("d", "d")); // []

NavigableSet<E> tailSet (E fromElement)

Returns a view of the portion of this set whose elements are greater than or equal to fromElement.

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]

final var tailSet = set.tailSet("b");
System.out.println(tailSet); // [b, c]

set.add("d");

System.out.println(set); // [a, b, c, d]
System.out.println(tailSet); // [b, c, d]

tailSet.remove("b");

System.out.println(set); // [a, c, d]
System.out.println(tailSet); // [c, d]

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]

System.out.println(set.tailSet("a")); // [a, b, c]
System.out.println(set.tailSet("b")); // [b, c]
System.out.println(set.tailSet("c")); // [c]
System.out.println(set.tailSet("d")); // []

NavigableSet<E> tailSet (E fromElement, boolean inclusive)

Returns a view of the portion of this set whose elements are greater than (or equal to, if inclusive is true) fromElement.

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]

final var tailSet = set.tailSet("a", false);
System.out.println(tailSet); // [b, c]

set.add("d");

System.out.println(set); // [a, b, c, d]
System.out.println(tailSet); // [b, c, d]

tailSet.remove("b");

System.out.println(set); // [a, c, d]
System.out.println(tailSet); // [c, d]

final var set = new ConcurrentSkipListSet<String>();
set.add("a");
set.add("b");
set.add("c");

System.out.println(set); // [a, b, c]

System.out.println(set.tailSet("a")); // [a, b, c]
System.out.println(set.tailSet("a", false)); // [b, c]

System.out.println(set.tailSet("b")); // [b, c]
System.out.println(set.tailSet("b", false)); // [c]

System.out.println(set.tailSet("c")); // [c]
System.out.println(set.tailSet("c", false)); // []

hashCode

Please see the link below.

• Java API Examples : AbstractSet

addAll, containsAll, retainAll, toArray, toArray, toString

Please see the link below.

• Java API Examples : AbstractCollection

parallelStream, removeIf, stream, toArray

Please see the link below.

• Java API Examples : Collection

forEach

Please see the link below.

• Java API Examples : Iterable

addAll, containsAll, hashCode, retainAll, toArray, toArray

Please see the link below.

• Java API Examples : Set