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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) 2013, 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.hash;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Holder;
import org.javimmutable.collections.Holders;
import org.javimmutable.collections.JImmutableMap;
import org.javimmutable.collections.common.MutableDelta;
import org.javimmutable.collections.cursors.LazyCursor;
import org.javimmutable.collections.cursors.MultiTransformCursor;
import org.javimmutable.collections.list.JImmutableLinkedStack;

public class HashTrieMultiValue
        implements HashTrieValue
{
    private final JImmutableLinkedStack> values;

    public HashTrieMultiValue(JImmutableLinkedStack> values)
    {
        this.values = values;
    }

    @Override
    public Holder getValueForKey(K key)
    {
        final JImmutableLinkedStack> values = this.values;
        for (JImmutableLinkedStack> list = values; !list.isEmpty(); list = list.getTail()) {
            if (list.getHead().getKey().equals(key)) {
                return Holders.of(list.getHead().getValue());
            }
        }
        return Holders.of();
    }

    @Override
    public JImmutableMap.Entry getEntryForKey(K key)
    {
        final JImmutableLinkedStack> values = this.values;
        for (JImmutableLinkedStack> list = values; !list.isEmpty(); list = list.getTail()) {
            if (list.getHead().getKey().equals(key)) {
                return list.getHead();
            }
        }
        return null;
    }

    @Override
    public HashTrieValue setValueForKey(K key,
                                              V value,
                                              MutableDelta sizeDelta)
    {
        final JImmutableLinkedStack> values = this.values;
        JImmutableLinkedStack> newList = JImmutableLinkedStack.of();
        boolean found = false;
        for (JImmutableLinkedStack> list = values; !list.isEmpty(); list = list.getTail()) {
            final HashTrieSingleValue head = list.getHead();
            if (head.getKey().equals(key)) {
                if (head.getValue() == value) {
                    return this;
                }
                found = true;
            } else {
                newList = newList.insert(head);
            }
        }
        newList = newList.insert(new HashTrieSingleValue(key, value));
        if (!found) {
            sizeDelta.add(1);
        }
        return new HashTrieMultiValue(newList);
    }

    @Override
    public HashTrieValue deleteValueForKey(K key,
                                                 MutableDelta sizeDelta)
    {
        boolean found = false;
        JImmutableLinkedStack> newList = JImmutableLinkedStack.of();
        for (JImmutableLinkedStack> list = values; !list.isEmpty(); list = list.getTail()) {
            final HashTrieSingleValue entry = list.getHead();
            if (entry.getKey().equals(key)) {
                found = true;
            } else {
                newList = newList.insert(entry);
            }
        }
        if (found) {
            sizeDelta.subtract(1);
            if (newList.isEmpty()) {
                return null;
            } else if (newList.getTail().isEmpty()) {
                return newList.getHead();
            } else {
                return new HashTrieMultiValue(newList);
            }
        } else {
            return this;
        }
    }

    @Override
    public int size()
    {
        int total = 0;
        JImmutableLinkedStack> values = this.values;
        while (!values.isEmpty()) {
            total += 1;
            values = values.getTail();
        }
        return total;
    }

    @Override
    public Cursor> cursor()
    {
        return MultiTransformCursor.of(LazyCursor.of(values), HashTrieValueToEntryCursorFunc.of());
    }
}