    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 * </p>
    032 *
    033 * @param <K> the type of objects that may be compared by this analyzer
    034 * @since 4.0
    035 */
    036public abstract class KeyAnalyzer<K> implements Comparator<K>, Serializable {
    037
    038    /** Serialization version */
    039    private static final long serialVersionUID = -20497563720380683L;
    040
    041    /**
    042     * Returned by {@link #bitIndex(Object, int, int, Object, int, int)}
    043     * if key's bits are all 0.
    044     */
    045    public static final int NULL_BIT_KEY = -1;
    046
    047    /**
    048     * Returned by {@link #bitIndex(Object, int, int, Object, int, int)} if key and found key are equal.
    049     * This is a very, very specific case and shouldn't happen on a regular basis.
    050     */
    051    public static final int EQUAL_BIT_KEY = -2;
    052
    053    public static final int OUT_OF_BOUNDS_BIT_KEY = -3;
    054
    055    /**
    056     * Returns true if bitIndex is a {@link KeyAnalyzer#EQUAL_BIT_KEY}.
    057     */
    058    static boolean isEqualBitKey(final int bitIndex) {
    059        return bitIndex == EQUAL_BIT_KEY;
    060    }
    061
    062    /**
    063     * Returns true if bitIndex is a {@link KeyAnalyzer#NULL_BIT_KEY}.
    064     */
    065    static boolean isNullBitKey(final int bitIndex) {
    066        return bitIndex == NULL_BIT_KEY;
    067    }
    068
    069    /**
    070     * Returns true if bitIndex is a {@link KeyAnalyzer#OUT_OF_BOUNDS_BIT_KEY}.
    071     */
    072    static boolean isOutOfBoundsIndex(final int bitIndex) {
    073        return bitIndex == OUT_OF_BOUNDS_BIT_KEY;
    074    }
    075
    076    /**
    077     * Returns true if the given bitIndex is valid.
    078     * Indices are considered valid if they're between 0 and {@link Integer#MAX_VALUE}
    079     */
    080    static boolean isValidBitIndex(final int bitIndex) {
    081        return bitIndex >= 0;
    082    }
    083
    084    /**
    085     * Returns the n-th different bit between key and other. This starts the comparison in
    086     * key at 'offsetInBits' and goes for 'lengthInBits' bits, and compares to the other key starting
    087     * at 'otherOffsetInBits' and going for 'otherLengthInBits' bits.
    088     *
    089     * @param key  the key to use
    090     * @param offsetInBits  the bit offset in the key
    091     * @param lengthInBits  the maximum key length in bits to use
    092     * @param other  the other key to use
    093     * @param otherOffsetInBits  the bit offset in the other key
    094     * @param otherLengthInBits  the maximum key length in bits for the other key
    095     * @return the bit index where the key and other first differ
    096     */
    097    public abstract int bitIndex(K key, int offsetInBits, int lengthInBits,
    098                                 K other, int otherOffsetInBits, int otherLengthInBits);
    099
    100    /**
    101     * Returns the number of bits per element in the key.
    102     * This is only useful for variable-length keys, such as Strings.
    103     *
    104     * @return the number of bits per element
    105     */
    106    public abstract int bitsPerElement();
    107
    108    @Override
    109    @SuppressWarnings("unchecked")
    110    public int compare(final K o1, final K o2) {
    111        if (o1 == null) {
    112            return o2 == null ? 0 : -1;
    113        }
    114        if (o2 == null) {
    115            return 1;
    116        }
    117
    118        return ((Comparable<K>) o1).compareTo(o2);
    119    }
    120
    121    /**
    122     * Returns whether or not a bit is set.
    123     *
    124     * @param key  the key to check, may not be null
    125     * @param bitIndex  the bit index to check
    126     * @param lengthInBits  the maximum key length in bits to check
    127     * @return {@code true} if the bit is set in the given key and
    128     *   {@code bitIndex} &lt; {@code lengthInBits}, {@code false} otherwise.
    129     */
    130    public abstract boolean isBitSet(K key, int bitIndex, int lengthInBits);
    131
    132    /**
    133     * Determines whether or not the given prefix (from offset to length) is a prefix of the given key.
    134     *
    135     * @param prefix  the prefix to check
    136     * @param offsetInBits  the bit offset in the key
    137     * @param lengthInBits  the maximum key length in bits to use
    138     * @param key  the key to check
    139     * @return {@code true} if this is a valid prefix for the given key
    140     */
    141    public abstract boolean isPrefix(K prefix, int offsetInBits, int lengthInBits, K key);
    142
    143    /**
    144     * Returns the length of the Key in bits.
    145     *
    146     * @param key  the key
    147     * @return the bit length of the key
    148     */
    149    public abstract int lengthInBits(K key);
    150
    151}