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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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//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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package org.javimmutable.collections.tree;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Holder;
import org.javimmutable.collections.SplitableIterator;
import org.javimmutable.collections.common.AbstractJImmutableMap;
import org.javimmutable.collections.common.Conditions;
import org.javimmutable.collections.common.StreamConstants;
import org.javimmutable.collections.serialization.JImmutableTreeMapProxy;

import javax.annotation.Nonnull;
import javax.annotation.concurrent.Immutable;
import java.io.Serializable;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

@Immutable
public class JImmutableTreeMap
    extends AbstractJImmutableMap
    implements Serializable
{
    private static final Comparator EMPTY_COMPARATOR = ComparableComparator.of();
    @SuppressWarnings("unchecked")
    private static final JImmutableTreeMap EMPTY = new JImmutableTreeMap(EMPTY_COMPARATOR, EmptyNode.of(), 0);

    private static final long serialVersionUID = -121805;

    private final Comparator comparator;
    private final Node root;
    private final int size;

    private JImmutableTreeMap(@Nonnull Comparator comparator,
                              @Nonnull Node root,
                              int size)
    {
        this.comparator = comparator;
        this.root = root;
        this.size = size;
    }

    @SuppressWarnings("unchecked")
    @Nonnull
    public static , V> JImmutableTreeMap of()
    {
        return EMPTY;
    }

    @Nonnull
    public static  JImmutableTreeMap of(@Nonnull Comparator comparator)
    {
        return new JImmutableTreeMap<>(comparator, EmptyNode.of(), 0);
    }

    /**
     * Constructs a new map containing the same key/value pairs as map using a ComparableComparator
     * to compare the keys.
     */
    @Nonnull
    @Deprecated
    public static , V> JImmutableTreeMap of(Map map)
    {
        JImmutableTreeMap answer = of();
        for (Map.Entry entry : map.entrySet()) {
            answer = answer.assign(entry.getKey(), entry.getValue());
        }
        return answer;
    }

    @Override
    public V getValueOr(K key,
                        V defaultValue)
    {
        Conditions.stopNull(key);
        return root.getValueOr(comparator, key, defaultValue);
    }

    @Nonnull
    @Override
    public Holder find(@Nonnull K key)
    {
        Conditions.stopNull(key);
        return root.find(comparator, key);
    }

    @Nonnull
    @Override
    public Holder> findEntry(@Nonnull K key)
    {
        Conditions.stopNull(key);
        return root.findEntry(comparator, key);
    }

    @Nonnull
    @Override
    public JImmutableTreeMap assign(@Nonnull K key,
                                          V value)
    {
        Conditions.stopNull(key);
        final UpdateResult result = root.assign(comparator, key, value);
        switch (result.type) {
            case UNCHANGED:
                return this;
            case INPLACE:
                return new JImmutableTreeMap<>(comparator, result.newNode, size + result.sizeDelta);
            case SPLIT:
                return new JImmutableTreeMap<>(comparator, new BranchNode<>(result.newNode, result.extraNode), size + result.sizeDelta);
            default:
                throw new IllegalStateException("unknown UpdateResult.Type value");
        }
    }

    @Nonnull
    @Override
    public JImmutableTreeMap delete(@Nonnull K key)
    {
        Conditions.stopNull(key);
        final Node newRoot = root.delete(comparator, key);
        if (newRoot == root) {
            return this;
        } else if (size == 1) {
            return deleteAll();
        } else {
            return new JImmutableTreeMap<>(comparator, newRoot.compress(), size - 1);
        }
    }

    @Override
    public int size()
    {
        return size;
    }

    @Nonnull
    @Override
    public JImmutableTreeMap deleteAll()
    {
        return (comparator == EMPTY_COMPARATOR) ? EMPTY : new JImmutableTreeMap<>(comparator, EmptyNode.of(), 0);
    }

    @Nonnull
    @Override
    public Cursor> cursor()
    {
        return root.cursor();
    }

    @Override
    public int getSpliteratorCharacteristics()
    {
        return StreamConstants.SPLITERATOR_ORDERED;
    }

    @Nonnull
    @Override
    public SplitableIterator> iterator()
    {
        return root.iterator();
    }

    @Override
    public void checkInvariants()
    {
        root.checkInvariants(comparator);
    }

    @Nonnull
    public Comparator getComparator()
    {
        return comparator;
    }

    @Nonnull
    List getKeysList()
    {
        List keys = new LinkedList<>();
        for (Entry entry : this) {
            keys.add(entry.getKey());
        }
        return Collections.unmodifiableList(keys);
    }

    private Object writeReplace()
    {
        return new JImmutableTreeMapProxy(this);
    }
}