Class List.Nil<T>

java.lang.Object
io.vavr.collection.List.Nil<T>
Type Parameters:
T - Component type of the List.
All Implemented Interfaces:
Foldable<T>, LinearSeq<T>, List<T>, Seq<T>, Traversable<T>, Function1<Integer,T>, PartialFunction<Integer,T>, Value<T>, Serializable, Iterable<T>, Function<Integer,T>
Enclosing interface:
List<T>
public static final class List.Nil<T> extends Object implements List<T>, Serializable
Representation of the singleton empty List.
See Also:

  • Field Details

    • serialVersionUID

      private static final long serialVersionUID
      See Also:

    • INSTANCE

      private static final List.Nil<?> INSTANCE

  • Constructor Details

    • Nil

      private Nil()

  • Method Details

    • instance

      public static <T> List.Nil<T> instance()
      Returns the singleton instance of the linked list.
      Type Parameters:
      T - Component type of the List
      Returns:
      the singleton instance of the linked list.

    • head

      public T head()
      Description copied from interface: Traversable
      Returns the first element of this non-empty Traversable.
      Specified by:
      head in interface Traversable<T>
      Returns:
      the first element

    • length

      public int length()
      Description copied from interface: Traversable
      Returns the number of elements in this Traversable.

      Equivalent to Traversable.size().

      Specified by:
      length in interface List<T>
      Specified by:
      length in interface Traversable<T>
      Returns:
      the number of elements

    • tail

      public List<T> tail()
      Description copied from interface: Traversable
      Returns a new Traversable without its first element.
      Specified by:
      tail in interface LinearSeq<T>
      Specified by:
      tail in interface List<T>
      Specified by:
      tail in interface Seq<T>
      Specified by:
      tail in interface Traversable<T>
      Returns:
      a new Traversable containing all elements except the first

    • isEmpty

      public boolean isEmpty()
      Description copied from interface: Traversable
      Checks if this Traversable contains no elements.
      Specified by:
      isEmpty in interface List<T>
      Specified by:
      isEmpty in interface Traversable<T>
      Specified by:
      isEmpty in interface Value<T>
      Returns:
      true if empty, false otherwise

    • equals

      public boolean equals(Object o)
      Description copied from interface: Traversable
      Determines whether this collection is equal to the given object.

      In Vavr, there are four basic collection types:

      • Seq – sequential elements
      • Set – distinct elements
      • Map – key-value pairs
      • Multimap – keys mapped to multiple values
      Two collections are considered equal if and only if:
      • They are of the same collection type (Seq, Set, Map, Multimap)
      • They contain the same elements
      • For Seq, the element order is the same

      For Map and Multimap, two entries (key1, value1) and (key2, value2) are equal if both their keys and values are equal.

      Additional notes:

      • No collection equals null (e.g., Queue(1) != null)
      • Null elements are allowed and treated as expected (e.g., List(null, 1) == Stream(null, 1), HashMap((null,1)) == LinkedHashMap((null,1)))
      • Element order matters only for Seq
      • Other collection classes are equal if their types and elements (in iteration order) are equal
      • Iterators are compared by reference only
      Specified by:
      equals in interface Traversable<T>
      Specified by:
      equals in interface Value<T>
      Overrides:
      equals in class Object
      Parameters:
      o - the object to compare with, may be null
      Returns:
      true if the collections are equal according to the rules above, false otherwise

    • hashCode

      public int hashCode()
      Description copied from interface: Traversable
      Returns the hash code of this collection.

      Vavr distinguishes between collections with predictable iteration order (like Seq) and collections with arbitrary iteration order (like Set, Map, and Multimap). In all cases, the hash of an empty collection is defined as 1.

      For collections with predictable iteration order, the hash is computed as:

      int hash = 1;
for (T t : this) {
    hash = hash * 31 + Objects.hashCode(t);
}

      For collections with arbitrary iteration order, the hash is computed to be independent of element order:

      int hash = 1;
for (T t : this) {
    hash += Objects.hashCode(t);
}

      Note that these algorithms may change in future Vavr versions. Hash codes are generally not cached, unlike size/length, because caching would increase memory usage due to persistent tree-based structures. Computing the hash code is linear in time, O(n). For frequently re-used collections (e.g., as HashMap keys), caching can be done externally using a wrapper, for example:

      public final class Hashed<K> {
    private final K key;
    private final Lazy<Integer> hashCode;

    public Hashed(K key) {
        this.key = key;
        this.hashCode = Lazy.of(() -> Objects.hashCode(key));
    }

    public K key() { return key; }

    @Override
    public boolean equals(Object o) {
        if (o == key) return true;
        if (key != null && o instanceof Hashed) return key.equals(((Hashed<?>) o).key);
        return false;
    }

    @Override
    public int hashCode() { return hashCode.get(); }

    @Override
    public String toString() { return "Hashed(" + key + ")"; }
}
      Specified by:
      hashCode in interface Traversable<T>
      Specified by:
      hashCode in interface Value<T>
      Overrides:
      hashCode in class Object
      Returns:
      the hash code of this collection

    • toString

      public String toString()
      Description copied from interface: Value
      Clarifies that values have a proper toString() method implemented.

      See Object.toString().

      Specified by:
      toString in interface Value<T>
      Overrides:
      toString in class Object
      Returns:
      A String representation of this object

    • readResolve

      private Object readResolve()
      Instance control for object serialization.
      Returns:
      The singleton instance of Nil.
      See Also: