В этом руководстве мы узнаем о классе Java TreeSet и его различных операциях и методах с помощью примеров.
TreeSetКласс рамках коллекции Java обеспечивает функциональные структуры данных дерева.
Он расширяет интерфейс NavigableSet.
Создание TreeSet
Чтобы создать древовидный набор, мы должны java.util.TreeSetсначала импортировать пакет.
После импорта пакета вот как мы можем создать TreeSetв Java.
TreeSet numbers = new TreeSet();
Здесь мы создали TreeSetбез аргументов. В этом случае элементы в TreeSetсортируются естественным образом (в порядке возрастания).
Однако мы можем настроить сортировку элементов с помощью Comparatorинтерфейса. Мы узнаем об этом позже в этом уроке.
Методы TreeSet
TreeSetКласс предоставляет различные методы , которые позволяют выполнять различные операции на множестве.
Вставить элементы в TreeSet
add()- вставляет указанный элемент в наборaddAll()- вставляет все элементы указанной коллекции в набор
Например,
import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet evenNumbers = new TreeSet(); // Using the add() method evenNumbers.add(2); evenNumbers.add(4); evenNumbers.add(6); System.out.println("TreeSet: " + evenNumbers); TreeSet numbers = new TreeSet(); numbers.add(1); // Using the addAll() method numbers.addAll(evenNumbers); System.out.println("New TreeSet: " + numbers); ) )
Вывод
TreeSet: (2, 4, 6) Новый TreeSet: (1, 2, 4, 6)
Доступ к элементам TreeSet
Чтобы получить доступ к элементам древовидного набора, мы можем использовать iterator()метод. Чтобы использовать этот метод, мы должны импортировать java.util.Iteratorpackage. Например,
import java.util.TreeSet; import java.util.Iterator; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(6); System.out.println("TreeSet: " + numbers); // Calling iterator() method Iterator iterate = numbers.iterator(); System.out.print("TreeSet using Iterator: "); // Accessing elements while(iterate.hasNext()) ( System.out.print(iterate.next()); System.out.print(", "); ) ) )
Вывод
TreeSet: (2, 5, 6) TreeSet с использованием Iterator: 2, 5, 6,
Удалить элементы
remove()- удаляет указанный элемент из набораremoveAll()- удаляет все элементы из набора
Например,
import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using the remove() method boolean value1 = numbers.remove(5); System.out.println("Is 5 removed? " + value1); // Using the removeAll() method boolean value2 = numbers.removeAll(numbers); System.out.println("Are all elements removed? " + value2); ) )
Вывод
TreeSet: (2, 5, 6) 5 удалено? true Все элементы удалены? правда
Способы навигации
Поскольку TreeSetкласс реализует NavigableSet, он предоставляет различные методы для навигации по элементам набора дерева.
1. Методы first () и last ()
first()- возвращает первый элемент набораlast()- возвращает последний элемент набора
Например,
import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using the first() method int first = numbers.first(); System.out.println("First Number: " + first); // Using the last() method int last = numbers.last(); System.out.println("Last Number: " + last); ) )
Вывод
TreeSet: (2, 5, 6) Первое число: 2 Последнее число: 6
2. Методы потолка (), пола (), выше () и ниже ()
- выше (элемент) - возвращает самый низкий элемент среди тех элементов, которые больше указанного
element. - lower(element) - Returns the greatest element among those elements that are less than the specified
element. - ceiling(element) - Returns the lowest element among those elements that are greater than the specified element. If the element passed exists in a tree set, it returns the
elementpassed as an argument. - floor(element) - Returns the greatest element among those elements that are less than the specified
element. If the element passed exists in a tree set, it returns theelementpassed as an argument.
For example,
import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(4); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using higher() System.out.println("Using higher: " + numbers.higher(4)); // Using lower() System.out.println("Using lower: " + numbers.lower(4)); // Using ceiling() System.out.println("Using ceiling: " + numbers.ceiling(4)); // Using floor() System.out.println("Using floor: " + numbers.floor(3)); ) )
Output
TreeSet: (2, 4, 5, 6) Using higher: 5 Using lower: 2 Using ceiling: 4 Using floor: 2
3. pollfirst() and pollLast() Methods
pollFirst()- returns and removes the first element from the setpollLast()- returns and removes the last element from the set
For example,
import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(4); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using pollFirst() System.out.println("Removed First Element: " + numbers.pollFirst()); // Using pollLast() System.out.println("Removed Last Element: " + numbers.pollLast()); System.out.println("New TreeSet: " + numbers); ) )
Output
TreeSet: (2, 4, 5, 6) Removed First Element: 2 Removed Last Element: 6 New TreeSet: (4, 5)
4. headSet(), tailSet() and subSet() Methods
headSet(element, booleanValue)
The headSet() method returns all the elements of a tree set before the specified element (which is passed as an argument).
The booleanValue parameter is optional. Its default value is false.
If true is passed as a booleanValue, the method returns all the elements before the specified element including the specified element.
For example,
import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(4); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using headSet() with default boolean value System.out.println("Using headSet without boolean value: " + numbers.headSet(5)); // Using headSet() with specified boolean value System.out.println("Using headSet with boolean value: " + numbers.headSet(5, true)); ) )
Output
TreeSet: (2, 4, 5, 6) Using headSet without boolean value: (2, 4) Using headSet with boolean value: (2, 4, 5)
tailSet(element, booleanValue)
The tailSet() method returns all the elements of a tree set after the specified element (which is passed as a parameter) including the specified element.
The booleanValue parameter is optional. Its default value is true.
If false is passed as a booleanValue, the method returns all the elements after the specified element without including the specified element.
For example,
import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(4); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using tailSet() with default boolean value System.out.println("Using tailSet without boolean value: " + numbers.tailSet(4)); // Using tailSet() with specified boolean value System.out.println("Using tailSet with boolean value: " + numbers.tailSet(4, false)); ) )
Output
TreeSet: (2, 4, 5, 6) Using tailSet without boolean value: (4, 5, 6) Using tailSet with boolean value: (5, 6)
subSet(e1, bv1, e2, bv2)
The subSet() method returns all the elements between e1 and e2 including e1.
The bv1 and bv2 are optional parameters. The default value of bv1 is true, and the default value of bv2 is false.
If false is passed as bv1, the method returns all the elements between e1 and e2 without including e1.
If true is passed as bv2, the method returns all the elements between e1 and e2, including e1.
For example,
import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(4); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using subSet() with default boolean value System.out.println("Using subSet without boolean value: " + numbers.subSet(4, 6)); // Using subSet() with specified boolean value System.out.println("Using subSet with boolean value: " + numbers.subSet(4, false, 6, true)); ) )
Output
TreeSet: (2, 4, 5, 6) Using subSet without boolean value: (4, 5) Using subSet with boolean value: (5, 6)
Set Operations
The methods of the TreeSet class can also be used to perform various set operations.
Union of Sets
To perform the union between two sets, we use the addAll() method. For example,
import java.util.TreeSet;; class Main ( public static void main(String() args) ( TreeSet evenNumbers = new TreeSet(); evenNumbers.add(2); evenNumbers.add(4); System.out.println("TreeSet1: " + evenNumbers); TreeSet numbers = new TreeSet(); numbers.add(1); numbers.add(2); numbers.add(3); System.out.println("TreeSet2: " + numbers); // Union of two sets numbers.addAll(evenNumbers); System.out.println("Union is: " + numbers); ) )
Output
TreeSet1: (2, 4) TreeSet2: (1, 2, 3) Union is: (1, 2, 3, 4)
Intersection of Sets
To perform the intersection between two sets, we use the retainAll() method. For example,
import java.util.TreeSet;; class Main ( public static void main(String() args) ( TreeSet evenNumbers = new TreeSet(); evenNumbers.add(2); evenNumbers.add(4); System.out.println("TreeSet1: " + evenNumbers); TreeSet numbers = new TreeSet(); numbers.add(1); numbers.add(2); numbers.add(3); System.out.println("TreeSet2: " + numbers); // Intersection of two sets numbers.retainAll(evenNumbers); System.out.println("Intersection is: " + numbers); ) )
Output
TreeSet1: (2, 4) TreeSet2: (1, 2, 3) Intersection is: (2)
Difference of Sets
To calculate the difference between the two sets, we can use the removeAll() method. For example,
import java.util.TreeSet;; class Main ( public static void main(String() args) ( TreeSet evenNumbers = new TreeSet(); evenNumbers.add(2); evenNumbers.add(4); System.out.println("TreeSet1: " + evenNumbers); TreeSet numbers = new TreeSet(); numbers.add(1); numbers.add(2); numbers.add(3); numbers.add(4); System.out.println("TreeSet2: " + numbers); // Difference between two sets numbers.removeAll(evenNumbers); System.out.println("Difference is: " + numbers); ) )
Output
TreeSet1: (2, 4) TreeSet2: (1, 2, 3, 4) Difference is: (1, 3)
Subset of a Set
To check if a set is a subset of another set or not, we use the containsAll() method. For example,
import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(1); numbers.add(2); numbers.add(3); numbers.add(4); System.out.println("TreeSet1: " + numbers); TreeSet primeNumbers = new TreeSet(); primeNumbers.add(2); primeNumbers.add(3); System.out.println("TreeSet2: " + primeNumbers); // Check if primeNumbers is subset of numbers boolean result = numbers.containsAll(primeNumbers); System.out.println("Is TreeSet2 subset of TreeSet1? " + result); ) )
Output
TreeSet1: (1, 2, 3, 4) TreeSet2: (2, 3) Is TreeSet2 subset of TreeSet1? True
Other Methods of TreeSet
| Method | Description |
|---|---|
clone() | Creates a copy of the TreeSet |
contains() | Searches the TreeSet for the specified element and returns a boolean result |
isEmpty() | Checks if the TreeSet is empty |
size() | Returns the size of the TreeSet |
clear() | Removes all the elements from the TreeSet |
To learn more, visit Java TreeSet (official Java documentation).
TreeSet Vs. HashSet
Both the TreeSet as well as the HashSet implements the Set interface. However, there exist some differences between them.
- Unlike
HashSet, elements inTreeSetare stored in some order. It is becauseTreeSetimplements theSortedSetinterface as well. TreeSetprovides some methods for easy navigation. For example,first(),last(),headSet(),tailSet(), etc. It is becauseTreeSetalso implements theNavigableSetinterface.HashSetis faster than theTreeSetfor basic operations like add, remove, contains and size.
TreeSet Comparator
In all the examples above, tree set elements are sorted naturally. However, we can also customize the ordering of elements.
For this, we need to create our own comparator class based on which elements in a tree set are sorted. For example,
import java.util.TreeSet; import java.util.Comparator; class Main ( public static void main(String() args) ( // Creating a tree set with customized comparator TreeSet animals = new TreeSet(new CustomComparator()); animals.add("Dog"); animals.add("Zebra"); animals.add("Cat"); animals.add("Horse"); System.out.println("TreeSet: " + animals); ) // Creating a comparator class public static class CustomComparator implements Comparator ( @Override public int compare(String animal1, String animal2) ( int value = animal1.compareTo(animal2); // elements are sorted in reverse order if (value> 0) ( return -1; ) else if (value < 0) ( return 1; ) else ( return 0; ) ) ) )
Output
TreeSet: (Zebra, Horse, Dog, Cat)
In the above example, we have created a tree set passing CustomComparator class as an argument.
Класс CustomComparator реализует Comparatorинтерфейс.
Затем мы переопределяем compare()метод. Теперь метод будет сортировать элементы в обратном порядке.
Чтобы узнать больше, посетите Java Comparator (официальная документация по Java).
