Java TreeSet (med eksempler)

I denne vejledning lærer vi om Java TreeSet-klassen og dens forskellige operationer og metoder ved hjælp af eksempler.

Den TreeSetklasse af Java kollektioner rammer giver funktionaliteten af et træ datastruktur.

Det udvider NavigableSet-grænsefladen.

Oprettelse af et tresæt

For at oprette et tresæt skal vi først importere java.util.TreeSetpakken.

Når vi først har importeret pakken, kan du oprette en TreeSeti Java her.

  TreeSet numbers = new TreeSet();

Her har vi oprettet en TreeSetuden argumenter. I dette tilfælde TreeSetsorteres elementerne i naturligt (stigende rækkefølge).

Vi kan dog tilpasse sorteringen af ​​elementer ved hjælp af Comparatorgrænsefladen. Vi lærer om det senere i denne vejledning.

Metoder til TreeSet

Den TreeSetklasse giver forskellige metoder, der tillader os at udføre forskellige operationer på sættet.

Indsæt elementer i TreeSet

  • add() - indsætter det angivne element i sættet
  • addAll() - indsætter alle elementerne i den angivne samling i sættet

For eksempel,

 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); ) )

Produktion

 TreeSet: (2, 4, 6) New TreeSet: (1, 2, 4, 6)

Adgang til TreeSet Elements

For at få adgang til elementerne i et tresæt kan vi bruge iterator()metoden. For at kunne bruge denne metode skal vi importere java.util.Iteratorpakken. For eksempel,

 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(", "); ) ) )

Produktion

 TreeSet: (2, 5, 6) TreeSet ved hjælp af Iterator: 2, 5, 6,

Fjern elementer

  • remove() - fjerner det angivne element fra sættet
  • removeAll() - fjerner alle elementerne fra sættet

For eksempel,

 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); ) )

Produktion

TreeSet: (2, 5, 6) Er 5 fjernet? sand Er alle elementer fjernet? sand

Metoder til navigation

Da TreeSetklassen implementeres NavigableSet, giver den forskellige metoder til at navigere over elementerne i træsættet.

1. Første () og sidste () metode

  • first() - returnerer det første element i sættet
  • last() - returnerer det sidste element i sættet

For eksempel,

 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); ) )

Produktion

 TreeSet: (2, 5, 6) Første nummer: 2 Sidste nummer: 6

2. Loft (), gulv (), højere () og lavere () Metoder

  • højere (element) - Returnerer det laveste element blandt de elementer, der er større end det angivne element.
  • lavere (element) - Returnerer det største element blandt de elementer, der er mindre end det angivne element.
  • loft (element) - Returnerer det laveste element blandt de elementer, der er større end det angivne element. Hvis elementet bestået findes i et tresæt, returnerer det det elementbestået som et argument.
  • gulv (element) - Returnerer det største element blandt de elementer, der er mindre end det specificerede element. Hvis elementet bestået findes i et tresæt, returnerer det det elementbestået som et argument.

For eksempel,

 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)); ) )

Produktion

 TreeSet: (2, 4, 5, 6) Brug af højere: 5 Brug af nedre: 2 Brug af loft: 4 Brug af gulv: 2

3. pollfirst () og pollLast () -metoder

  • pollFirst() - returnerer og fjerner det første element fra sættet
  • pollLast() - returnerer og fjerner det sidste element fra sættet

For eksempel,

 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); ) )

Produktion

 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 in TreeSet are stored in some order. It is because TreeSet implements the SortedSet interface as well.
  • TreeSet provides some methods for easy navigation. For example, first(), last(), headSet(), tailSet(), etc. It is because TreeSet also implements the NavigableSet interface.
  • HashSet is faster than the TreeSet 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.

CustomComparator-klassen implementerer Comparatorgrænsefladen.

Vi tilsidesætter derefter compare()metoden. Metoden sorterer nu elementer i omvendt rækkefølge.

For at lære mere, besøg Java Comparator (officiel Java-dokumentation).

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