Created: 2023-09-03 20:50
Status: #concept
Subject: Programming
Tags: Java java.util Java Interface java.util.Collection

java.util.Set

A collection that contains no duplicate elements. More formally, sets contain no pair of elements e1 and e2 such that e1.equals(e2), and at most one null element.

As implied by its name, this interface models the mathematical Set concept.

All Known Implementing Classes:

AbstractSet, ConcurrentHashMap.KeySetView, ConcurrentSkipListSet, CopyOnWriteArraySet, EnumSet, HashSet, JobStateReasons, LinkedHashSet, TreeSet

Set<String> set = new HashSet<>();
set.add("one");
set.add("one");
set.add("two");

for (String element: set) {
    System.out.println(element);
}

// one 
// two

If objects created from custom classes are added to the HashSet object, they must have both the equals and hashCode methods defined.

java.util.Set

References