JAVA: Class Collection di Java
Class Collection adalah anggota dari Java Collections Framework. Paket java.util.Collections adalah paket yang berisi class Collection. Class Collection pada dasarnya digunakan dengan method statis yang beroperasi pada collection atau return sebuah collection. Semua method class ini throw NullPointerException jika collection atau object yang diteruskan ke method adalah null.
Syntax: Declaration
public class Collections extends Object
Ingat: Object adalah parent class dari semua class.
Collection class field
collection class pada dasarnya berisi 3 field seperti yang tercantum di bawah ini yang dapat digunakan untuk mengembalikan entitas yang tidak dapat diubah.
- EMPTY_LIST untuk mendapatkan Daftar kosong yang tidak dapat diubah
- EMPTY_SET untuk mendapatkan Set kosong yang tidak dapat diubah
- EMPTY_MAP untuk mendapatkan Peta kosong yang tidak dapat diubah
Sekarang mari kita membahas method yang ada di dalam class ini sehingga kita dapat mengimplementasikan fungsionalitas bawaan ini nanti dalam program kita. Di bawah ini adalah method yang tercantum di bawah ini dalam format tabel seperti yang ditunjukkan di bawah ini sebagai berikut:
| Methods | Description |
|---|---|
| addAll(Collection<? extends E> c) | It is used to insert the specified collection elements in the invoking collection. |
| asLifoQueue(Deque<T> deque) | This method returns a view of a Deque as a Last-in-first-out (Lifo) Queue. |
| binarySearch(List<? extends Comparable> list, T key) | This method searches the key using binary search in the specified list. |
| binarySearch(List<? extends T> list, T key, Comparator<? super T> c) | This method searches the specified list for the specified object using the binary search algorithm. |
| checkedCollection(Collection<E> c, Class<E> type) | This method returns a dynamically typesafe view of the specified collection. |
| checkedList(List<E> list, Class<E> type) | This method returns a dynamically typesafe view of the specified list. |
| checkedMap(Map<K,V> m, Class<K> keyType, Class<V> valueType) | This method returns a dynamically typesafe view of the specified map. |
| checkedNavigableMap(NavigableMap<K,V> m, Class<K> keyType, Class<V> valueType) | This method returns a dynamically typesafe view of the specified navigable map. |
| checkedNavigableSet(NavigableSet<E> s, Class<E> type) | This method returns a dynamically typesafe view of the specified navigable set. |
| checkedQueue(Queue<E> queue, Class<E> type) | This method returns a dynamically typesafe view of the specified queue. |
| checkedSet(Set<E> s, Class<E> type) | This method returns a dynamically typesafe view of the specified set. |
| checkedSortedMap(SortedMap<K,V> m, Class<K> keyType, Class<V> valueType) | This method returns a dynamically typesafe view of the specified sorted map. |
| checkedSortedSet(SortedSet<E> s, Class<E> type) | This method returns a dynamically typesafe view of the specified sorted set. |
| copy(List<? super T> dest, List<? extends T> src) | This method copies all of the elements from one list into another. |
| disjoint(Collection<?> c1, Collection<?> c2) | This method returns true if the two specified collections have no elements in common. |
| emptyEnumeration() | This method returns an enumeration that has no elements. |
| emptyIterator() | This method returns an iterator that has no elements. |
| emptyList() | This method returns an empty list (immutable). |
| emptyListIterator() | This method returns a list iterator that has no elements. |
| emptyMap() | This method returns an empty map (immutable). |
| emptyNavigableMap() | This method returns an empty navigable map (immutable). |
| emptyNavigableSet() | This method returns an empty navigable set (immutable). |
| emptySet() | This method returns an empty set (immutable). |
| emptySortedMap() | This method returns an empty sorted map (immutable). |
| emptySortedSet() | This method returns an empty sorted set (immutable). |
| enumeration(Collection<T> c) | This method returns an enumeration over the specified collection. |
| fill(List<? super T> list, T obj) | This method replaces all of the elements of the specified list with the specified element. |
| frequency(Collection<?> c, Object o) | This method returns the number of elements in the specified collection equal to the specified object. |
| indexOfSubList(List<?> source, List<?> target) | This method returns the starting position of the first occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence. |
| lastIndexOfSubList(List<?> source, List<?> target) | This method returns the starting position of the last occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence. |
| list(Enumeration<T> e) | This method returns an array list containing the elements returned by the specified enumeration in the order they are returned by the enumeration. |
| max(Collection<? extends T> coll) | This method returns the maximum element of the given collection, according to the natural ordering of its elements. |
| max(Collection<? extends T> coll, Comparator<? super T> comp) | This method returns the maximum element of the given collection, according to the order induced by the specified comparator. |
| min(Collection<? extends T> coll) | This method returns the minimum element of the given collection, according to the natural ordering of its elements. |
| min(Collection<? extends T> coll, Comparator<? super T> comp) | This method returns the minimum element of the given collection, according to the order induced by the specified comparator. |
| nCopies(int n, T o) | This method returns an immutable list consisting of n copies of the specified object. |
| newSetFromMap(Map<E,Boolean> map) | This method returns a set backed by the specified map. |
| replaceAll(List<T> list, T oldVal, T newVal) | This method replaces all occurrences of one specified value in a list with another. |
| reverse(List<?> list) | This method reverses the order of the elements in the specified list |
| reverseOrder() | This method returns a comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface. |
| reverseOrder(Comparator<T> cmp) | This method returns a comparator that imposes the reverse ordering of the specified comparator. |
| rotate(List<?> list, int distance) | This method rotates the elements in the specified list by the specified distance. |
| shuffle(List<?> list) | This method randomly permutes the specified list using a default source of randomness. |
| shuffle(List<?> list, Random rnd) | This method randomly permute the specified list using the specified source of randomness. |
| singletonMap(K key, V value) | This method returns an immutable map, mapping only the specified key to the specified value. |
| singleton(T o) | This method returns an immutable set containing only the specified object. |
| singletonList(T o) | This method returns an immutable list containing only the specified object. |
| sort(List<T> list) | This method sorts the specified list into ascending order, according to the natural ordering of its elements. |
| sort(List<T> list, Comparator<? super T> c) | This method sorts the specified list according to the order induced by the specified comparator. |
| swap(List<?> list, int i, int j) | This method swaps the elements at the specified positions in the specified list. |
| synchronizedCollection(Collection<T> c) | This method returns a synchronized (thread-safe) collection backed by the specified collection. |
| synchronizedList(List<T> list) | This method returns a synchronized (thread-safe) list backed by the specified list. |
| synchronizedMap(Map<K,V> m) | This method returns a synchronized (thread-safe) map backed by the specified map. |
| synchronizedNavigableMap(NavigableMap<K,V> m) | This method returns a synchronized (thread-safe) navigable map backed by the specified navigable map. |
| synchronizedNavigableSet(NavigableSet<T> s) | This method returns a synchronized (thread-safe) navigable set backed by the specified navigable set. |
| synchronizedSet(Set<T> s) | This method returns a synchronized (thread-safe) set backed by the specified set. |
| synchronizedSortedMap(SortedMap<K,V> m) | This method returns a synchronized (thread-safe) sorted map backed by the specified sorted map. |
| synchronizedSortedSet(SortedSet<T> s) | This method returns a synchronized (thread-safe) sorted set backed by the specified sorted set. |
| unmodifiableCollection(Collection<? extends T> c) | This method returns an unmodifiable view of the specified collection. |
| unmodifiableList(List<? extends T> list) | This method returns an unmodifiable view of the specified list. |
| unmodifiableNavigableMap(NavigableMap<K,? extends V> m) | This method returns an unmodifiable view of the specified navigable map. |
| unmodifiableNavigableSet(NavigableSet<T> s) | This method returns an unmodifiable view of the specified navigable set. |
| unmodifiableSet(Set<? extends T> s) | This method returns an unmodifiable view of the specified set. |
| unmodifiableSortedMap(SortedMap<K,? extends V> m) | This method returns an unmodifiable view of the specified sorted map. |
| unmodifiableSortedSet(SortedSet<T> s) | This method returns an unmodifiable view of the specified sorted set. |
Tampak di atas adalah semua method yang ada, sehingga kita memiliki sedikit petunjuk agar bisa memahami betapa pentingnya method ini ketika berpikir tentang perspektif pemrograman global. Method penting dan sering digunakan secara luas saat menulis code yang dioptimalkan. Sialnya entah bagaimana mungkin karena ketidak pahaman akan konsep, optimalisasi code Java dengan Class Collection kadang menjadi kacau. Jadi di sini kemungkinan besar di class mana pun kita tidak hanya akan mengimplementasikan method tetapi juga akan membahas operasi yang dapat dilakukan sehingga seseorang dapat memiliki kejelasan konseptual dan perintah yang kuat saat mengimplementasikan hal yang sama. Operasi yang akan kita bahas adalah sebagai berikut:
- Menambahkan elemen ke Collection
- Sort Collection
- Search di Collection
- Copy Elemen
- Disjoint / Pisah Collection
Operation 1: Menambahkan Element ke Collection class object
The addAll() method of java.util.Collections class is used to add all the specified elements to the specified collection. Elements to be added may be specified individually or as an array.
Metode addAll() dari kelas java.util.Collections digunakan untuk menambahkan semua elemen yang ditentukan ke koleksi yang ditentukan. Elemen yang akan ditambahkan dapat ditentukan secara individual atau sebagai array.
Contoh
// Java Program to Demonstrate Adding Elements
// Using addAll() method
// Importing required classes
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
// Main class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating a list
// Declaring object of string type
List<String> items = new ArrayList<>();
// Adding elements (items) to the list
items.add("Shoes");
items.add("Toys");
// Add one or more elements
Collections.addAll(items, "Fruits", "Bat", "Ball");
// Printing the list contents
for (int i = 0; i < items.size(); i++) {
System.out.print(items.get(i) + " ");
}
}
}
Output
Shoes Toys Fruits Bat Ball
Operation 2: Sorting a Collection
java.util.Collections.sort() is used to sort the elements present in the specified list of Collection in ascending order. java.util.Collections.reverseOrder() is used to sort in the descending order.
java.util.Collections.sort() digunakan untuk mengurutkan elemen yang ada dalam daftar Koleksi yang ditentukan dalam urutan menaik. java.util.Collections.reverseOrder() digunakan untuk mengurutkan dalam urutan menurun.
Contoh
// Java program to demonstrate sorting
// a Collections using sort() method
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
// Main Class
// SortingCollectionExample
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating a list
// Declaring object of string type
List<String> items = new ArrayList<>();
// Adding elements to the list
// using add() method
items.add("Shoes");
items.add("Toys");
// Adding one or more elements using addAll()
Collections.addAll(items, "Fruits", "Bat", "Mouse");
// Sorting according to default ordering
// using sort() method
Collections.sort(items);
// Printing the elements
for (int i = 0; i < items.size(); i++) {
System.out.print(items.get(i) + " ");
}
System.out.println();
// Sorting according to reverse ordering
Collections.sort(items, Collections.reverseOrder());
// Printing the reverse order
for (int i = 0; i < items.size(); i++) {
System.out.print(items.get(i) + " ");
}
}
}
Output
Bat Fruits Mouse Shoes Toys Toys Shoes Mouse Fruits Bat
Operation 3: Searching in a Collection
java.util.Collections.binarySearch() method returns the position of an object in a sorted list. To use this method, the list should be sorted in ascending order, otherwise, the result returned from the method will be wrong. If the element exists in the list, the method will return the position of the element in the sorted list, otherwise, the result returned by the method would be the – (insertion point where the element should have been present if exist)-1).
java.util.Collections.binarySearch() method returns the position of an object in a sorted list. To use this method, the list should be sorted in ascending order, otherwise, the result returned from the method will be wrong. If the element exists in the list, the method will return the position of the element in the sorted list, otherwise, the result returned by the method would be the – (insertion point where the element should have been present if exist)-1).
Contoh
// Java Program to Demonstrate Binary Search
// Using Collections.binarySearch()
// Importing required classes
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
// Main class
// BinarySearchOnACollection
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating a List
// Declaring object of string type
List<String> items = new ArrayList<>();
// Adding elements to object
// using add() method
items.add("Shoes");
items.add("Toys");
items.add("Horse");
items.add("Ball");
items.add("Grapes");
// Sort the List
Collections.sort(items);
// BinarySearch on the List
System.out.println(
"The index of Horse is "
+ Collections.binarySearch(items, "Horse"));
// BinarySearch on the List
System.out.println(
"The index of Dog is "
+ Collections.binarySearch(items, "Dog"));
}
}
Output
The index of Horse is 2 The index of Dog is -2
Operation 4: Copying Elements
The copy() method of java.util.Collections class is used to copy all the elements from one list into another. After the operation, the index of each copied element in the destination list will be identical to its index in the source list. The destination list must be at least as long as the source list. If it is longer, the remaining elements in the destination list are unaffected.
Metode copy() dari kelas java.util.Collections digunakan untuk menyalin semua elemen dari satu daftar ke daftar lainnya. Setelah operasi, indeks setiap elemen yang disalin dalam daftar tujuan akan identik dengan indeksnya dalam daftar sumber. Daftar tujuan harus setidaknya sepanjang daftar sumber. Jika lebih panjang, elemen yang tersisa dalam daftar tujuan tidak terpengaruh.
Contoh
// Java Program to Demonstrate Copying Elements
// Using copy() method
// Importing required classes
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
// Main class
// CopyOneCollectionToAnother
class GFG {
// Main driver method
public static void main(String[] args)
{
// Create destination list
List<String> destination_List = new ArrayList<>();
// Add elements
destination_List.add("Shoes");
destination_List.add("Toys");
destination_List.add("Horse");
destination_List.add("Tiger");
// Print the elements
System.out.println(
"The Original Destination list is ");
for (int i = 0; i < destination_List.size(); i++) {
System.out.print(destination_List.get(i) + " ");
}
System.out.println();
// Create source list
List<String> source_List = new ArrayList<>();
// Add elements
source_List.add("Bat");
source_List.add("Frog");
source_List.add("Lion");
// Copy the elements from source to destination
Collections.copy(destination_List, source_List);
// Printing the modified list
System.out.println(
"The Destination List After copying is ");
for (int i = 0; i < destination_List.size(); i++) {
System.out.print(destination_List.get(i) + " ");
}
}
}
Output
The Original Destination list is Shoes Toys Horse Tiger The Destination List After copying is Bat Frog Lion Tiger
Operation 5: Disjoint Collection
java.util.Collections.disjoint() is used to check whether two specified collections are disjoint or not. More formally, two collections are disjoint if they have no elements in common. It returns true if the two collections do not have any element in common.
java.util.Collections.disjoint() digunakan untuk memeriksa apakah dua koleksi yang ditentukan terpisah atau tidak. Secara lebih formal, dua koleksi dikatakan terpisah jika tidak memiliki elemen yang sama. Ini mengembalikan true jika dua koleksi tidak memiliki elemen yang sama.
Contoh
// Java Program to Illustrate Working of Disjoint Function
// Importing required classes
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
// Main class
// DisjointCollectionsExample
class GFG {
// Main driver method
public static void main(String[] args)
{
// Create list1
List<String> list1 = new ArrayList<>();
// Add elements to list1
list1.add("Shoes");
list1.add("Toys");
list1.add("Horse");
list1.add("Tiger");
// Create list2
List<String> list2 = new ArrayList<>();
// Add elements to list2
list2.add("Bat");
list2.add("Frog");
list2.add("Lion");
// Check if disjoint or not
System.out.println(
Collections.disjoint(list1, list2));
}
}
Output
true