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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) 2014, Burton Computer Corporation
// All rights reserved.
//
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//
//     Redistributions in binary form must reproduce the above copyright
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package org.javimmutable.collections.tree;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Holder;
import org.javimmutable.collections.common.AbstractJImmutableMap;
import org.javimmutable.collections.common.Conditions;
import org.javimmutable.collections.common.MutableDelta;

import javax.annotation.Nonnull;
import javax.annotation.concurrent.Immutable;
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
{
    @SuppressWarnings("unchecked")
    private static final JImmutableTreeMap EMPTY = new JImmutableTreeMap(new ComparableComparator());

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

    /**
     * Constructs an empty map using the specified Comparator.  Note that the Comparator MUST BE IMMUTABLE.
     * The Comparator will be retained and used throughout the life of the map and its offspring and will
     * be aggressively shared so it is imperative that the Comparator be completely immutable.
     *
     * @param comparator
     */
    private JImmutableTreeMap(Comparator comparator)
    {
        this(comparator, EmptyNode.of(), 0);
    }

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

    /**
     * Constructs an empty map using the specified Comparator.  Note that the Comparator MUST BE IMMUTABLE.
     * The Comparator will be retained and used throughout the life of the map and its offspring and will
     * be aggressively shared so it is imperative that the Comparator be completely immutable.
     *
     * @param comparator
     */
    public static  JImmutableTreeMap of(Comparator comparator)
    {
        return new JImmutableTreeMap(comparator);
    }

    /**
     * Constructs a new map containing the same key/value pairs as map using a ComparableComparator
     * to compare the keys.
     *
     * @param map
     * @param 
     * @param 
     * @return
     */
    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;
    }

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

    @Override
    public V getValueOr(K key,
                        V defaultValue)
    {
        if (key == null) {
            throw new NullPointerException();
        }
        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);
        MutableDelta sizeDelta = new MutableDelta();
        TreeNode newRoot = root.assign(comparator, key, value, sizeDelta);
        if (newRoot == root) {
            return this;
        } else {
            return create(newRoot, sizeDelta.getValue());
        }
    }

    @Nonnull
    @Override
    public JImmutableTreeMap delete(@Nonnull K key)
    {
        Conditions.stopNull(key);
        MutableDelta sizeDelta = new MutableDelta();
        TreeNode newRoot = root.delete(comparator, key, sizeDelta);
        if (newRoot == root) {
            return this;
        } else {
            return create(newRoot, sizeDelta.getValue());
        }
    }

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

    @Nonnull
    @Override
    public JImmutableTreeMap deleteAll()
    {
        return of(comparator);
    }

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

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

    public void verifyDepthsMatch()
    {
        root.verifyDepthsMatch();
    }

    public Comparator getComparator()
    {
        return comparator;
    }

    private JImmutableTreeMap create(TreeNode root,
                                           int sizeDelta)
    {
        return new JImmutableTreeMap(comparator, root, size + sizeDelta);
    }
}