Java TreeSet (Dengan Contoh)

Dalam tutorial ini, kita akan belajar tentang kelas Java TreeSet dan berbagai operasi dan metodenya dengan bantuan contoh.

The TreeSetkelas dari koleksi kerangka Java menyediakan fungsi struktur data pohon.

Ini memperluas antarmuka NavigableSet.

Membuat TreeSet

Untuk membuat kumpulan pohon, kita harus mengimpor java.util.TreeSetpaket terlebih dahulu.

Setelah kami mengimpor paket, berikut adalah cara membuat TreeSetdi Java.

  TreeSet numbers = new TreeSet();

Di sini, kami telah membuat TreeSettanpa argumen. Dalam hal ini, elemen dalam TreeSetdiurutkan secara alami (urutan naik).

Namun, kami dapat menyesuaikan penyortiran elemen dengan menggunakan Comparatorantarmuka. Kita akan mempelajarinya nanti di tutorial ini.

Metode TreeSet

The TreeSetkelas menyediakan berbagai metode yang memungkinkan kita untuk melakukan berbagai operasi di set.

Masukkan Elemen ke TreeSet

  • add() - menyisipkan elemen yang ditentukan ke set
  • addAll() - menyisipkan semua elemen dari koleksi yang ditentukan ke set

Sebagai contoh,

 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); ) )

Keluaran

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

Akses Elemen TreeSet

Untuk mengakses elemen dari kumpulan pohon, kita bisa menggunakan iterator()metode. Untuk menggunakan metode ini, kita harus mengimpor java.util.Iteratorpaket. Sebagai contoh,

 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(", "); ) ) )

Keluaran

 TreeSet: (2, 5, 6) TreeSet menggunakan Iterator: 2, 5, 6,

Hapus Elemen

  • remove() - menghapus elemen tertentu dari set
  • removeAll() - menghapus semua elemen dari set

Sebagai contoh,

 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); ) )

Keluaran

TreeSet: (2, 5, 6) Apakah 5 dihapus? true Apakah semua elemen dihilangkan? benar

Metode Navigasi

Sejak TreeSetmengimplementasikan kelas NavigableSet, ia menyediakan berbagai metode untuk menavigasi elemen dari kumpulan pohon.

1. Metode pertama () dan terakhir ()

  • first() - mengembalikan elemen pertama dari set
  • last() - mengembalikan elemen terakhir dari set

Sebagai contoh,

 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); ) )

Keluaran

 TreeSet: (2, 5, 6) Nomor Pertama: 2 Nomor Terakhir: 6

2. Metode langit-langit (), lantai (), lebih tinggi () dan bawah ()

  • lebih tinggi (elemen) - Mengembalikan elemen terendah di antara elemen yang lebih besar dari yang ditentukan element.
  • lower (elemen) - Mengembalikan elemen terbesar di antara elemen-elemen yang lebih kecil dari yang ditentukan element.
  • langit-langit (elemen) - Mengembalikan elemen terendah di antara elemen yang lebih besar dari elemen yang ditentukan. Jika elemen yang diteruskan ada dalam kumpulan pohon, ia mengembalikan yang elementditeruskan sebagai argumen.
  • floor (elemen) - Menampilkan elemen terbesar di antara elemen-elemen yang kurang dari yang ditentukan element. Jika elemen yang diteruskan ada dalam kumpulan pohon, ia mengembalikan yang elementditeruskan sebagai argumen.

Sebagai contoh,

 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)); ) )

Keluaran

 TreeSet: (2, 4, 5, 6) Menggunakan lebih tinggi: 5 Menggunakan bawah: 2 Menggunakan langit-langit: 4 Menggunakan lantai: 2

3. Metode pollfirst () dan pollLast ()

  • pollFirst() - mengembalikan dan menghapus elemen pertama dari set
  • pollLast() - mengembalikan dan menghapus elemen terakhir dari set

Sebagai contoh,

 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); ) )

Keluaran

 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.

Kelas CustomComparator mengimplementasikan Comparatorantarmuka.

Kami kemudian mengganti compare()metode tersebut. Metode ini sekarang akan mengurutkan elemen dalam urutan terbalik.

Untuk mempelajari lebih lanjut, kunjungi Java Comparator (dokumentasi resmi Java).

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