Class Tree.Empty<T>

java.lang.Object
io.vavr.collection.Tree.Empty<T>
Type Parameters:
T - type of the tree's values
All Implemented Interfaces:
Foldable<T>, Traversable<T>, Tree<T>, Value<T>, Serializable, Iterable<T>
Enclosing interface:
Tree<T>
public static final class Tree.Empty<T> extends Object implements Tree<T>, Serializable
The empty tree. Use Tree.empty() to create an instance.
See Also:

  • Field Details

  • Constructor Details

    • Empty

      private Empty()

  • Method Details

    • instance

      public static <T> Tree.Empty<T> instance()

    • getChildren

      public List<Tree.Node<T>> getChildren()
      Description copied from interface: Tree
      Returns the children of this tree.
      Specified by:
      getChildren in interface Tree<T>
      Returns:
      the tree's children

    • getValue

      public T getValue()
      Description copied from interface: Tree
      Gets the value of this tree.
      Specified by:
      getValue in interface Tree<T>
      Returns:
      The value of this tree.

    • isEmpty

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

    • length

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

      Same as Traversable.size().

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

    • isLeaf

      public boolean isLeaf()
      Description copied from interface: Tree
      Checks if this Tree is a leaf. A tree is a leaf if it is a Node with no children. Because the empty tree is no Node, it is not a leaf by definition.
      Specified by:
      isLeaf in interface Tree<T>
      Returns:
      true if this tree is a leaf, false otherwise.

    • last

      public T last()
      Description copied from interface: Traversable
      Dual of Traversable.head(), returning the last element.
      Specified by:
      last in interface Traversable<T>
      Returns:
      the last element.

    • equals

      public boolean equals(Object o)
      Description copied from interface: Traversable
      In Vavr there are four basic classes of collections:
      • Seq (sequential elements)
      • Set (distinct elements)
      • Map (indexed elements)
      • Multimap (indexed collections)
      Two collection instances of these classes are equal if and only if both collections
      • belong to the same basic collection class (Seq, Set, Map or Multimap)
      • contain the same elements
      • have the same element order, if the collections are of type Seq
      Two Map/Multimap elements, resp. entries, (key1, value1) and (key2, value2) are equal, if the keys are equal and the values are equal.

      Notes:

      • No collection instance equals null, e.g. Queue(1) not equals null.
      • Nulls are allowed and handled as expected, e.g. List(null, 1) equals Stream(null, 1) and HashMap((null, 1)) equals LinkedHashMap((null, 1)).
      • The element order is taken into account for Seq only. E.g. List(null, 1) not equals Stream(1, null) and HashMap((null, 1), ("a", null)) equals LinkedHashMap(("a", null), (null, 1)). The reason is, that we do not know which implementations we compare when having two instances of type Map, Multimap or Set (see Liskov Substitution Principle).
      • Other collection classes are equal if their types are equal and their elements are equal (in iteration order).
      • Iterator equality is defined to be object reference equality.
      Specified by:
      equals in interface Traversable<T>
      Specified by:
      equals in interface Tree<T>
      Specified by:
      equals in interface Value<T>
      Overrides:
      equals in class Object
      Parameters:
      o - an object, may be null
      Returns:
      true, if this collection equals the given object according to the rules described above, false otherwise.

    • hashCode

      public int hashCode()
      Description copied from interface: Traversable
      Returns the hash code of this collection.
      We distinguish between two types of hashes, those for collections with predictable iteration order (like Seq) and those with arbitrary iteration order (like Set, Map and Multimap).
      In all cases the hash of an empty collection is defined to be 1.
      Collections with predictable iteration order are hashed as follows: 
      int hash = 1;
for (T t : this) { hash = hash * 31 + Objects.hashCode(t); }
      Collections with arbitrary iteration order are hashed in a way such that the hash of a fixed number of elements is independent of their iteration order. 
      int hash = 1;
for (T t : this) { hash += Objects.hashCode(t); }
      Please note that the particular hashing algorithms may change in a future version of Vavr.
      Generally, hash codes of collections aren't cached in Vavr (opposed to the size/length). Storing hash codes in order to reduce the time complexity would increase the memory footprint. Persistent collections are built upon tree structures, it allows us to implement efficient memory sharing. A drawback of tree structures is that they make it necessary to store collection attributes at each tree node (read: element).
      The computation of the hash code is linear in time, i.e. O(n). If the hash code of a collection is re-calculated often, e.g. when using a List as HashMap key, we might want to cache the hash code. This can be achieved by simply using a wrapper class, which is not included in Vavr but could be implemented like this: 
      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;
    }

    &#64;Override
    public boolean equals(Object o) {
        if (o == key) {
            return true;
        } else if (key != null && o instanceof Hashed) {
            final Hashed that = (Hashed) o;
            return key.equals(that.key);
        } else {
            return false;
        }
    }

    &#64;Override
    public int hashCode() {
        return hashCode.get();
    }

    &#64;Override
    public String toString() {
        return "Hashed(" + (key == null ? "null" : key.toString()) + ")";
    }
}
      Specified by:
      hashCode in interface Traversable<T>
      Specified by:
      hashCode in interface Tree<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 Tree<T>
      Specified by:
      toString in interface Value<T>
      Overrides:
      toString in class Object
      Returns:
      A String representation of this object

    • toLispString

      public String toLispString()
      Description copied from interface: Tree
      Creates a Lisp-like representation of this Tree.
      Specified by:
      toLispString in interface Tree<T>
      Returns:
      This Tree as Lisp-string, i.e. represented as list of lists.

    • draw

      public String draw()
      Description copied from interface: Tree
      Creates a neat 2-dimensional drawing of a tree. Unicode characters are used to draw node junctions.
      Specified by:
      draw in interface Tree<T>
      Returns:
      A nice string representation of the tree.

    • readResolve

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