U ovom ćemo uputstvu uz primjere naučiti o klasi Java TreeSet i njezinim raznim operacijama i metodama.
TreeSet
Klasa Java zbirki okvira pruža funkcionalnost strukture stabla podataka.
Proširuje sučelje NavigableSet.
Stvaranje skupa stabala
Da bismo stvorili skup stabala, prvo moramo uvesti java.util.TreeSet
paket.
Nakon što uvozimo paket, evo kako možemo stvoriti a TreeSet
u Javi.
TreeSet numbers = new TreeSet();
Ovdje smo stvorili TreeSet
bez ikakvih argumenata. U ovom se slučaju elementi u TreeSet
sortiraju prirodno (uzlazno).
Međutim, sortiranje elemenata možemo prilagoditi pomoću Comparator
sučelja. O tome ćemo saznati kasnije u ovom vodiču.
Metode TreeSet-a
TreeSet
Klasa pruža različite metode koje omogućuju nam da obavljaju različite operacije na setu.
Umetnite elemente u TreeSet
add()
- ubacuje navedeni element u skupaddAll()
- u skup ubacuje sve elemente navedene zbirke
Na primjer,
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); ) )
Izlaz
Set stabala: (2, 4, 6) Novi set stabala: (1, 2, 4, 6)
Pristupite elementima TreeSet
Za pristup elementima skupa stabala možemo koristiti iterator()
metodu. Da bismo koristili ovu metodu, moramo uvesti java.util.Iterator
paket. Na primjer,
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(", "); ) ) )
Izlaz
TreeSet: (2, 5, 6) TreeSet koristeći Iterator: 2, 5, 6,
Uklonite elemente
remove()
- uklanja navedeni element iz skuparemoveAll()
- uklanja sve elemente iz skupa
Na primjer,
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); ) )
Izlaz
TreeSet: (2, 5, 6) Je li uklonjeno 5? true Jesu li uklonjeni svi elementi? pravi
Metode za plovidbu
Budući da se TreeSet
klasa provodi NavigableSet
, ona pruža razne metode za navigaciju kroz elemente skupa stabala.
1. prva () i zadnja () metode
first()
- vraća prvi element skupalast()
- vraća zadnji element skupa
Na primjer,
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); ) )
Izlaz
Set stabala: (2, 5, 6) Prvi broj: 2 Zadnji broj: 6
2. Metode stropa (), poda (), više () i niže ()
- viši (element) - Vraća najniži element među onim elementima koji su veći od navedenog
element
. - donji (element) - Vraća najveći element među onim elementima koji su manji od navedenog
element
. - strop (element) - daje najniži element među onim elementima koji su veći od navedenog elementa. Ako preneseni element postoji u skupu stabala, vraća
element
prosljeđeni kao argument. - pod (element) - Vraća najveći element među onim elementima koji su manji od navedenog
element
. Ako preneseni element postoji u skupu stabala, vraćaelement
prosljeđeni kao argument.
Na primjer,
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)); ) )
Izlaz
TreeSet: (2, 4, 5, 6) Korištenje više: 5 Korištenje niže: 2 Korištenje stropa: 4 Korištenje poda: 2
3. metode pollfirst () i pollLast ()
pollFirst()
- vraća i uklanja prvi element iz skupapollLast()
- vraća i uklanja posljednji element iz skupa
Na primjer,
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); ) )
Izlaz
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 inTreeSet
are stored in some order. It is becauseTreeSet
implements theSortedSet
interface as well. TreeSet
provides some methods for easy navigation. For example,first()
,last()
,headSet(
),tailSet()
, etc. It is becauseTreeSet
also implements theNavigableSet
interface.HashSet
is faster than theTreeSet
for 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.
Klasa CustomComparator implementira Comparator
sučelje.
Zatim zamjenjujemo compare()
metodu. Metoda će sada sortirati elemente obrnutim redoslijedom.
Da biste saznali više, posjetite Java Comparator (službena Java dokumentacija).