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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.array.trie32;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Holder;
import org.javimmutable.collections.Holders;
import org.javimmutable.collections.Indexed;
import org.javimmutable.collections.JImmutableArray;
import org.javimmutable.collections.JImmutableMap;
import org.javimmutable.collections.common.AbstractJImmutableArray;
import org.javimmutable.collections.common.MutableDelta;

public class TrieArray
        extends AbstractJImmutableArray
{
    @SuppressWarnings("unchecked")
    private static final TrieArray EMPTY = new TrieArray(TrieNode.of(), 0);

    private final TrieNode root;
    private final int size;

    private TrieArray(TrieNode root,
                      int size)
    {
        this.root = root;
        this.size = size;
    }

    @SuppressWarnings("unchecked")
    public static  TrieArray of()
    {
        return (TrieArray)EMPTY;
    }

    public static  JImmutableArray of(Indexed source,
                                            int offset,
                                            int limit)
    {
        final int size = limit - offset;
        if (size == 0) {
            return of();
        }

        // small lists can be directly constructed from a single leaf array
        if (size <= 32) {
            return new TrieArray(TrieNode.fromSource(0, source, offset, limit), size);
        }

        // first construct an array containing a single level of arrays of leaves
        final int numBranches = Math.min(32, (limit - offset + 31) / 32);
        @SuppressWarnings("unchecked") final TrieNode[] branchArray = (TrieNode[])new TrieNode[numBranches];
        int index = 0;
        for (int b = 0; b < numBranches; ++b) {
            int branchSize = Math.min(32, limit - offset);
            branchArray[b] = TrieNode.fromSource(index, source, offset, limit);
            offset += branchSize;
            index += branchSize;
        }

        // then add any extras left over above that size
        JImmutableArray array = new TrieArray(MultiBranchTrieNode.forEntries(5, branchArray), index);
        while (offset < limit) {
            array = array.assign(index++, source.get(offset++));
        }
        return array;
    }

    @Override
    public T getValueOr(int index,
                        T defaultValue)
    {
        if (root.getShift() < TrieNode.shiftForIndex(index)) {
            return defaultValue;
        } else {
            return root.getValueOr(root.getShift(), index, defaultValue);
        }
    }

    @Override
    public Holder find(int index)
    {
        if (root.getShift() < TrieNode.shiftForIndex(index)) {
            return Holders.of();
        } else {
            return root.find(root.getShift(), index);
        }
    }

    @Override
    public JImmutableArray assign(int index,
                                     T value)
    {
        MutableDelta sizeDelta = new MutableDelta();
        TrieNode newRoot = root.paddedToMinimumDepthForShift(TrieNode.shiftForIndex(index));
        newRoot = newRoot.assign(newRoot.getShift(), index, value, sizeDelta);
        return (newRoot == root) ? this : new TrieArray(newRoot, size + sizeDelta.getValue());
    }

    @Override
    public JImmutableArray delete(int index)
    {
        if (root.getShift() < TrieNode.shiftForIndex(index)) {
            return this;
        } else {
            MutableDelta sizeDelta = new MutableDelta();
            final TrieNode newRoot = root.delete(root.getShift(), index, sizeDelta).trimmedToMinimumDepth();
            return (newRoot == root) ? this : new TrieArray(newRoot, size + sizeDelta.getValue());
        }
    }

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

    @Override
    public JImmutableArray deleteAll()
    {
        return of();
    }

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