Java : TreeSet with Examples
Last Modified : February 25, 2024 Published : July 2, 2022
TreeSet (Java SE 18 & JDK 18) API Examples.
You will find code examples on most TreeSet methods.
Summary
A NavigableSet implementation based on a TreeMap. The elements are ordered using their natural ordering, or by a Comparator provided at set creation time, depending on which constructor is used.
final var set = new TreeSet<String>();
System.out.println(set); // []
System.out.println(set.isEmpty()); // true
set.add("a");
set.add("b");
set.add("c");
System.out.println(set); // [a, b, c]
System.out.println(set.size()); // 3
System.out.println(set.contains("a")); // true
System.out.println(set.contains("b")); // true
System.out.println(set.contains("x")); // false
final var treeSet = new TreeSet<String>();
treeSet.add("ccc");
treeSet.add("ddd");
treeSet.add("aaa");
treeSet.add("bbb");
System.out.println(treeSet); // [aaa, bbb, ccc, ddd]
final var hashSet = new HashSet<String>();
hashSet.add("ccc");
hashSet.add("ddd");
hashSet.add("aaa");
hashSet.add("bbb");
System.out.println(hashSet); // [aaa, ccc, bbb, ddd]
Constructors
TreeSet ()
Constructs a new, empty tree set, sorted according to the natural ordering of its elements.
final var set = new TreeSet<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 TreeSet<Integer>();
set.add(100);
set.add(999);
set.add(-200);
System.out.println(set); // [-200, 100, 999]
TreeSet (Collection<? extends E> c)
Constructs a new tree set containing the elements in the specified collection, sorted according to the natural ordering of its elements.
final var c = List.of("b", "a", "c");
final var set = new TreeSet<>(c);
System.out.println(set); // [a, b, c]
System.out.println(set.size()); // 3
TreeSet (Comparator<? super E> comparator)
Constructs a new, empty tree set, sorted according to the specified comparator.
final var src = List.of("bbb", "aaa", "ccc");
final var set1 = new TreeSet<String>();
set1.addAll(src);
System.out.println(set1); // [aaa, bbb, ccc]
final var set2 = new TreeSet<String>(Comparator.reverseOrder());
set2.addAll(src);
System.out.println(set2); // [ccc, bbb, aaa]
TreeSet (SortedSet<E> s)
Constructs a new tree set containing the same elements and using the same ordering as the specified sorted set.
final var s = new TreeSet<String>(Comparator.reverseOrder());
s.add("a");
s.add("b");
s.add("c");
System.out.println(s); // [c, b, a]
final var set = new TreeSet<>(s);
System.out.println(set); // [c, b, a]
System.out.println(set.size()); // 3
Methods
boolean add (E e)
Adds the specified element to this set if it is not already present.
final var set = new TreeSet<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]
boolean addAll (Collection<? extends E> c)
Adds all of the elements in the specified collection to this set.
final var src = Set.of("a", "b", "c");
{
final var set = new TreeSet<>(src);
System.out.println(set); // [a, b, c]
System.out.println(set.addAll(Set.of("d", "e", "f"))); // true
System.out.println(set); // [a, b, c, d, e, f]
}
{
final var set = new TreeSet<>(src);
System.out.println(set); // [a, b, c]
System.out.println(set.addAll(Set.of("a", "b", "c"))); // false
System.out.println(set); // [a, b, c]
}
{
final var set = new TreeSet<>(src);
System.out.println(set); // [a, b, c]
System.out.println(set.addAll(Set.of("a", "c", "e", "f"))); // true
System.out.println(set); // [a, b, c, e, f]
}
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 TreeSet<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 TreeSet<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); // []
Object clone ()
Returns a shallow copy of this TreeSet instance.
final var set = new TreeSet<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.TreeSet
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 TreeSet<String>();
System.out.println(set); // []
final var comparator = set.comparator();
System.out.println(comparator); // null
final var set = new TreeSet<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 TreeSet<>(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 TreeSet<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 TreeSet<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 TreeSet<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]
E first ()
Returns the first (lowest) element currently in this set.
final var set = new TreeSet<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 TreeSet<String>();
System.out.println(set); // []
try {
set.first();
} catch (NoSuchElementException e) {
System.out.println(e);
}
// Result
// ↓
//java.util.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 TreeSet<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
SortedSet<E> headSet (E toElement)
Returns a view of the portion of this set whose elements are strictly less than toElement.
final var set = new TreeSet<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 TreeSet<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 TreeSet<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 TreeSet<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 TreeSet<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 TreeSet<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 TreeSet<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 TreeSet<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 TreeSet<String>();
System.out.println(set); // []
try {
set.last();
} catch (NoSuchElementException e) {
System.out.println(e);
}
// Result
// ↓
//java.util.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 TreeSet<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 TreeSet<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 TreeSet<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 TreeSet<>(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 TreeSet<>(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 TreeSet<>(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 TreeSet<>(src);
System.out.println(set); // [a, b, c]
System.out.println(set.remove("X")); // false
System.out.println(set); // [a, b, c]
}
int size ()
Returns the number of elements in this set (its cardinality).
final var set1 = new TreeSet<String>();
System.out.println(set1); // []
System.out.println(set1.size()); // 0
final var set2 = new TreeSet<String>();
Collections.addAll(set2, "a", "b", "c");
System.out.println(set2); // [a, b, c]
System.out.println(set2.size()); // 3
Spliterator<E> spliterator ()
Creates a late-binding and fail-fast Spliterator over the elements in this set.
final var set = new TreeSet<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 TreeSet<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 TreeSet<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)); // []
SortedSet<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 TreeSet<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 TreeSet<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")); // []
SortedSet<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 TreeSet<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 TreeSet<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 TreeSet<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 TreeSet<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)); // []
Methods declared in AbstractSet
Methods declared in AbstractCollection
containsAll, retainAll, toArray, toArray, toString
Please see the link below.
Methods declared in Collection
Methods declared in Iterable
Methods declared in Set
containsAll, equals, hashCode, removeAll, retainAll, toArray, toArray
Please see the link below.
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