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Library providing immutable/persistent collection classes for Java. While collections are immutable they provide methods for adding and removing values by creating new modified copies of themselves. Each copy shares almost all of its structure with other copies to minimize memory consumption.
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///###////////////////////////////////////////////////////////////////////////
//
// Burton Computer Corporation
// http://www.burton-computer.com
//
// Copyright (c) 2017, Burton Computer Corporation
// All rights reserved.
//
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//
//     Redistributions of source code must retain the above copyright
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//
//     Redistributions in binary form must reproduce the above copyright
//     notice, this list of conditions and the following disclaimer in
//     the documentation and/or other materials provided with the
//     distribution.
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package org.javimmutable.collections.tree;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Holder;
import org.javimmutable.collections.Holders;
import org.javimmutable.collections.JImmutableMap;
import org.javimmutable.collections.SplitableIterator;
import org.javimmutable.collections.Tuple2;
import org.javimmutable.collections.cursors.SingleValueCursor;
import org.javimmutable.collections.iterators.SingleValueIterator;

import javax.annotation.Nonnull;
import javax.annotation.concurrent.Immutable;
import java.util.Comparator;
import java.util.Objects;

@Immutable
public class LeafNode
    implements Node,
               JImmutableMap.Entry,
               Holder
{
    private final K key;
    private final V value;

    public LeafNode(@Nonnull K key,
                    V value)
    {
        this.key = key;
        this.value = value;
    }

    @Override
    public K baseKey()
    {
        return key;
    }

    @Override
    public int childCount()
    {
        return 1;
    }

    @Override
    public int valueCount()
    {
        return 1;
    }

    @Override
    public V getValueOr(@Nonnull Comparator comparator,
                        @Nonnull K key,
                        V defaultValue)
    {
        return comparator.compare(this.key, key) == 0 ? value : defaultValue;
    }

    @Nonnull
    @Override
    public Holder find(@Nonnull Comparator comparator,
                          @Nonnull K key)
    {
        return comparator.compare(this.key, key) == 0 ? this : Holders.of();
    }

    @Nonnull
    @Override
    public Holder> findEntry(@Nonnull Comparator comparator,
                                                       @Nonnull K key)
    {
        return comparator.compare(this.key, key) == 0 ? Holders.of(this) : Holders.of();
    }

    @Nonnull
    @Override
    public UpdateResult assign(@Nonnull Comparator comparator,
                                     @Nonnull K key,
                                     V value)
    {
        final LeafNode newLeaf = new LeafNode<>(key, value);
        final int diff = comparator.compare(this.key, key);
        if (diff == 0) {
            return (this.value == value) ? UpdateResult.createUnchanged() : UpdateResult.createInPlace(newLeaf, 0);
        } else {
            return (diff < 0) ? UpdateResult.createSplit(this, newLeaf, 1) : UpdateResult.createSplit(newLeaf, this, 1);
        }
    }

    @Nonnull
    @Override
    public Node delete(@Nonnull Comparator comparator,
                             @Nonnull K key)
    {
        final int diff = comparator.compare(this.key, key);
        return (diff == 0) ? EmptyNode.of() : this;
    }

    @Nonnull
    @Override
    public Node mergeChildren(@Nonnull Node sibling)
    {
        return new BranchNode<>(this, sibling);
    }

    @Nonnull
    @Override
    public Tuple2, Node> distributeChildren(@Nonnull Node sibling)
    {
        return Tuple2.of(this, sibling);
    }

    @Nonnull
    @Override
    public Node compress()
    {
        return this;
    }

    @Override
    public int depth()
    {
        return 0;
    }

    @Nonnull
    @Override
    public Cursor> cursor()
    {
        return SingleValueCursor.of(this);
    }

    @Nonnull
    @Override
    public SplitableIterator> iterator()
    {
        return SingleValueIterator.of(this);
    }

    @Override
    public void checkInvariants(@Nonnull Comparator comparator)
    {
    }

    @Nonnull
    @Override
    public K getKey()
    {
        return key;
    }

    @Override
    public V getValue()
    {
        return value;
    }

    @Override
    public boolean isEmpty()
    {
        return false;
    }

    @Override
    public boolean isFilled()
    {
        return true;
    }

    @Override
    public V getValueOrNull()
    {
        return value;
    }

    @Override
    public V getValueOr(V defaultValue)
    {
        return value;
    }

    @Override
    public String toString()
    {
        return "<" + key + "," + value + ">";
    }

    @Override
    public boolean equals(Object o)
    {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
        LeafNode leafNode = (LeafNode)o;
        return Objects.equals(key, leafNode.key) &&
               Objects.equals(value, leafNode.value);
    }

    @Override
    public int hashCode()
    {
        return Objects.hash(key, value);
    }
}