    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4.trie;
    018
    019import java.io.Serializable;
    020import java.util.Comparator;
    021
    022/**
    023 * Defines the interface to analyze {@link org.apache.commons.collections4.Trie Trie} keys on a bit level.
    024 * {@link KeyAnalyzer}'s methods return the length of the key in bits, whether or not a bit is set,
    025 * and bits per element in the key.
    026 * <p>
    027 * Additionally, a method determines if a key is a prefix of another
    028 * key and returns the bit index where one key is different from another
    029 * key (if the key and found key are equal than the return value is
    030 * {@link #EQUAL_BIT_KEY}).
    031 *
    032 * @param <K> the type of objects that may be compared by this analyzer
    033 * @since 4.0
    034 */
    035public abstract class KeyAnalyzer<K> implements Comparator<K>, Serializable {
    036
    037    /** Serialization version */
    038    private static final long serialVersionUID = -20497563720380683L;
    039
    040    /**
    041     * Returned by {@link #bitIndex(Object, int, int, Object, int, int)}
    042     * if key's bits are all 0.
    043     */
    044    public static final int NULL_BIT_KEY = -1;
    045
    046    /**
    047     * Returned by {@link #bitIndex(Object, int, int, Object, int, int)} if key and found key are equal.
    048     * This is a very very specific case and shouldn't happen on a regular basis.
    049     */
    050    public static final int EQUAL_BIT_KEY = -2;
    051
    052    public static final int OUT_OF_BOUNDS_BIT_KEY = -3;
    053
    054    /**
    055     * Returns true if bitIndex is a {@link KeyAnalyzer#OUT_OF_BOUNDS_BIT_KEY}.
    056     */
    057    static boolean isOutOfBoundsIndex(final int bitIndex) {
    058        return bitIndex == OUT_OF_BOUNDS_BIT_KEY;
    059    }
    060
    061    /**
    062     * Returns true if bitIndex is a {@link KeyAnalyzer#EQUAL_BIT_KEY}.
    063     */
    064    static boolean isEqualBitKey(final int bitIndex) {
    065        return bitIndex == EQUAL_BIT_KEY;
    066    }
    067
    068    /**
    069     * Returns true if bitIndex is a {@link KeyAnalyzer#NULL_BIT_KEY}.
    070     */
    071    static boolean isNullBitKey(final int bitIndex) {
    072        return bitIndex == NULL_BIT_KEY;
    073    }
    074
    075    /**
    076     * Returns true if the given bitIndex is valid.
    077     * Indices are considered valid if they're between 0 and {@link Integer#MAX_VALUE}
    078     */
    079    static boolean isValidBitIndex(final int bitIndex) {
    080        return bitIndex >= 0;
    081    }
    082
    083    /**
    084     * Returns the number of bits per element in the key.
    085     * This is only useful for variable-length keys, such as Strings.
    086     *
    087     * @return the number of bits per element
    088     */
    089    public abstract int bitsPerElement();
    090
    091    /**
    092     * Returns the length of the Key in bits.
    093     *
    094     * @param key  the key
    095     * @return the bit length of the key
    096     */
    097    public abstract int lengthInBits(K key);
    098
    099    /**
    100     * Returns whether or not a bit is set.
    101     *
    102     * @param key  the key to check, may not be null
    103     * @param bitIndex  the bit index to check
    104     * @param lengthInBits  the maximum key length in bits to check
    105     * @return {@code true} if the bit is set in the given key and
    106     *   {@code bitIndex} &lt; {@code lengthInBits}, {@code false} otherwise.
    107     */
    108    public abstract boolean isBitSet(K key, int bitIndex, int lengthInBits);
    109
    110    /**
    111     * Returns the n-th different bit between key and other. This starts the comparison in
    112     * key at 'offsetInBits' and goes for 'lengthInBits' bits, and compares to the other key starting
    113     * at 'otherOffsetInBits' and going for 'otherLengthInBits' bits.
    114     *
    115     * @param key  the key to use
    116     * @param offsetInBits  the bit offset in the key
    117     * @param lengthInBits  the maximum key length in bits to use
    118     * @param other  the other key to use
    119     * @param otherOffsetInBits  the bit offset in the other key
    120     * @param otherLengthInBits  the maximum key length in bits for the other key
    121     * @return the bit index where the key and other first differ
    122     */
    123    public abstract int bitIndex(K key, int offsetInBits, int lengthInBits,
    124                                 K other, int otherOffsetInBits, int otherLengthInBits);
    125
    126    /**
    127     * Determines whether or not the given prefix (from offset to length) is a prefix of the given key.
    128     *
    129     * @param prefix  the prefix to check
    130     * @param offsetInBits  the bit offset in the key
    131     * @param lengthInBits  the maximum key length in bits to use
    132     * @param key  the key to check
    133     * @return {@code true} if this is a valid prefix for the given key
    134     */
    135    public abstract boolean isPrefix(K prefix, int offsetInBits, int lengthInBits, K key);
    136
    137    @Override
    138    @SuppressWarnings("unchecked")
    139    public int compare(final K o1, final K o2) {
    140        if (o1 == null) {
    141            return o2 == null ? 0 : -1;
    142        } else if (o2 == null) {
    143            return 1;
    144        }
    145
    146        return ((Comparable<K>) o1).compareTo(o2);
    147    }
    148
    149}