README.md

public Class Collections extends Objects

• The Collections class is a utility class in Java that provides static methods for operating on collections (like lists, sets, etc.).
• It contains methods for searching, sorting, and manipulating collections.
• The Collections class cannot be instantiated, as it has a private constructor.
• It is part of the Java Collections Framework, which provides a set of classes and interfaces for working with groups of objects.
• The methods in this class throw NullPointerException if the collection provided is null.
• It contains polymorphic algorithms that operate on collections such as sort (sorting), binarySearch (searching), shuffle (randomizing the order of elements), and reverse (reversing the order of elements).
• UnsupportedOperationException is thrown by certain methods to indicate that the requested operation is not supported.

Fields

• public static final List EMPTY_LIST

  • Represents an empty, immutable list.

• public static final Set EMPTY_SET

  • Represents an empty, immutable set.

• public static final Map EMPTY_MAP

  • Represents an empty, immutable map.

Methods

• public static <T> boolean addAll(Collection<? super T> c, T... elements)

  • Adds all specified elements to the specified collection.

  • Returns true if the collection changed as a result of the call.

  • Sample Code

    ArrayList<String> teamAPlayers = new ArrayList<>();
    ArrayList<String> teamBPlayers = new ArrayList<>();
    ArrayList<String> players = new ArrayList<>();
    Collections.addAll(teamAPlayers, "Nani", "Ronaldo", "Pepe");
    Collections.addAll(teamBPlayers, "Di Maria", "Messi", "Otamendi");
        
    players.addAll(teamAPlayers);
    players.addAll(teamBPlayers);
    System.out.println("POR: {\'" + String.join("\', \'", teamAPlayers) + "\'}");
    System.out.println("ARG: {\'" + String.join("\', \'", teamBPlayers) + "\'}");
    System.out.println("ALL: {\'" + String.join("\', \'", players) + "\'}");

  • Output

    

Hierarchy

graph TD
    Object --> Collection
    Collection --> List
    Collection --> Set
    Collection --> Queue
    Set --> SortedSet
    SortedSet --> NavigableSet
    List --> ArrayList
    List --> LinkedList
    Set --> HashSet
    Set --> LinkedHashSet
    NavigableSet --> TreeSet
    Queue --> Deque
    Deque --> ArrayDeque

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