ConcurrentSkipListSet in Java with Examples

The ConcurrentSkipListSet class in Java is a part of the Java Collection Framework and implements the Collection interface and the AbstractSet class. It provides a scalable and concurrent version of NavigableSet in Java. The implementation of ConcurrentSkipListSet is based on ConcurrentSkipListMap. The elements in ConcurrentSkipListSet are sorted by default in their natural ordering.

Class Hierarchy:

java.lang.Object
   ? java.util.AbstractCollection<E>
      ? java.util.AbstractSet<E>
         ? Class ConcurrentSkipListSet<E>

Syntax:

public class ConcurrentSkipListSet<E>
    extends AbstractSet<E>
        implements NavigableSet<E>, Cloneable, Serializable

Where E is the type of elements maintained 
by this collection

Constructors in Java ConcurrentSkipListSet:

• ConcurrentSkipListSet(): This constructor is used to construct an empty set.
• ConcurrentSkipListSet(Collection<E> c): This constructor is used to construct a set with the elements of the Collection passed as the parameter.
• ConcurrentSkipListSet(Comparator<E> comparator): This constructor is used to construct a new, empty set that orders its elements according to the specified comparator.
• ConcurrentSkipListSet(SortedSet<E> s): This constructor is used to construct a new set containing the same elements and using the same ordering as the specified sorted set.

Below is a sample program to illustrate ConcurrentSkipListSet in Java:

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Output:

ConcurrentSkipListSet: [8, 12, 45, 64, 78]
ConcurrentSkipListSet1: [8, 12, 45, 64, 78]

Methods in Java ConcurrentSkipListSet:

1. add(E e): This method adds the specified element to this set if it is not already present.
2. ceiling(E e): This method returns the least element in this set greater than or equal to the given element, or null if there is no such element.
3. clear(): This method removes all of the elements from this set.
4. clone(): This method returns a shallow copy of this ConcurrentSkipListSet instance.
5. comparator(): This method returns the comparator used to order the elements in this set, or null if this set uses the natural ordering of its elements.
6. contains(Object o): This method returns true if this set contains the specified element.
7. descendingIterator(): This method returns an iterator over the elements in this set in descending order.
8. descending set(): This method returns a reverse order view of the elements contained in this set.
9. equals(Object o): This method compares the specified object with this set for equality.
10. first(): This method returns the first (lowest) element currently in this set.
11. floor(E e): This method returns the greatest element in this set less than or equal to the given element, or null if there is no such element.
12. headSet(E element): This method returns a view of the portion of this set whose elements are strictly less than toElement.
13. headSet(E element, boolean inclusive): This method returns a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement.
14. higher(E e): This method returns the least element in this set strictly greater than the given element, or null if there is no such element.
15. isEmpty(): This method returns true if this set contains no elements.
16. iterator(): This method returns an iterator over the elements in this set in ascending order.
17. last(): This method returns the last (highest) element currently in this set.
18. lower(E e): This method returns the greatest element in this set strictly less than the given element, or null if there is no such element.
19. pollFirst(): This method retrieves and removes the first (lowest) element, or returns null if this set is empty.
20. a poll last(): This method retrieves and removes the last (highest) element, or returns null if this set is empty.
21. remove(Object o): This method removes the specified element from this set if it is present.
22. removeAll(Collection<E> c): This method removes from this set all of its elements that are contained in the specified collection.
23. size(): This method returns the number of elements in this set.
24. spliterator(): This method returns a Spliterator over the elements in this set.
25. the subSet(E fromElement, boolean from inclusive, E element, boolean inclusive): This method returns a view of the portion of this set whose elements range from element to element.
26. the subSet(E fromElement, E element): This method returns a view of the portion of this set whose elements range from element, inclusive, to toElement, exclusive.
27. toilet(E from the element): This method returns a view of the portion of this set whose elements are greater than or equal to from element.
28. toilet(E fromElement, boolean inclusive): This method returns a view of the portion of this set whose elements are greater than (or equal to, if inclusive is true) from an element.

Example:

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Output:

ConcurrentSkipListSet: [8, 12, 45, 64, 78]
The highest element of the set: 78
The first element of the set: 8
9 is not present in the set.
Number of elements in the set = 4

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentSkipListSet.html