Package io.vavr.collection

Class Tree.Empty<T>

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

    • Constructor Detail

      • Empty

        private Empty()

    • Method Detail

      • instance

        public static <T> Tree.Empty<T> instance()
        Returns the singleton instance of the empty tree.
        Type Parameters:
        T - The component type
        Returns:
        The empty tree 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 contains no elements.
        Specified by:
        isEmpty in interface Traversable<T>
        Specified by:
        isEmpty in interface Value<T>
        Returns:
        true if empty, false otherwise

      • 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 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
        Returns the last element of this Traversable.
        Specified by:
        last in interface Traversable<T>
        Returns:
        the last element

      • equals

        public boolean equals​(java.lang.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 Tree<T>
        Specified by:
        equals in interface Value<T>
        Overrides:
        equals in class java.lang.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:

        {@code
 public final class Hashed {
     private final K key;
     private final Lazy hashCode;

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

     public K key() { return key; }
        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 java.lang.Object
        Returns:
        the hash code of this collection

      • toString

        public java.lang.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 java.lang.Object
        Returns:
        A String representation of this object

      • toLispString

        public java.lang.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 java.lang.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 java.lang.Object readResolve()
        Instance control for object serialization.
        Returns:
        The singleton instance of Nil.
        See Also:
        Serializable