    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 specific case and shouldn't happen on a regular basis.
    050     */
    051    public static final int EQUAL_BIT_KEY = -2;
    052
    053    /**
    054     * Used to test a {@code bitIndex} in {@link #isOutOfBoundsIndex(int)}.
    055     */
    056    public static final int OUT_OF_BOUNDS_BIT_KEY = -3;
    057
    058    /**
    059     * Returns true if bitIndex is a {@link KeyAnalyzer#EQUAL_BIT_KEY}.
    060     */
    061    static boolean isEqualBitKey(final int bitIndex) {
    062        return bitIndex == EQUAL_BIT_KEY;
    063    }
    064
    065    /**
    066     * Returns true if bitIndex is a {@link KeyAnalyzer#NULL_BIT_KEY}.
    067     */
    068    static boolean isNullBitKey(final int bitIndex) {
    069        return bitIndex == NULL_BIT_KEY;
    070    }
    071
    072    /**
    073     * Returns true if bitIndex is a {@link KeyAnalyzer#OUT_OF_BOUNDS_BIT_KEY}.
    074     */
    075    static boolean isOutOfBoundsIndex(final int bitIndex) {
    076        return bitIndex == OUT_OF_BOUNDS_BIT_KEY;
    077    }
    078
    079    /**
    080     * Returns true if the given bitIndex is valid.
    081     * Indices are considered valid if they're between 0 and {@link Integer#MAX_VALUE}
    082     */
    083    static boolean isValidBitIndex(final int bitIndex) {
    084        return bitIndex >= 0;
    085    }
    086
    087    /**
    088     * Returns the n-th different bit between key and other. This starts the comparison in
    089     * key at 'offsetInBits' and goes for 'lengthInBits' bits, and compares to the other key starting
    090     * at 'otherOffsetInBits' and going for 'otherLengthInBits' bits.
    091     *
    092     * @param key  the key to use
    093     * @param offsetInBits  the bit offset in the key
    094     * @param lengthInBits  the maximum key length in bits to use
    095     * @param other  the other key to use
    096     * @param otherOffsetInBits  the bit offset in the other key
    097     * @param otherLengthInBits  the maximum key length in bits for the other key
    098     * @return the bit index where the key and other first differ
    099     */
    100    public abstract int bitIndex(K key, int offsetInBits, int lengthInBits,
    101                                 K other, int otherOffsetInBits, int otherLengthInBits);
    102
    103    /**
    104     * Returns the number of bits per element in the key.
    105     * This is only useful for variable-length keys, such as Strings.
    106     *
    107     * @return the number of bits per element
    108     */
    109    public abstract int bitsPerElement();
    110
    111    @Override
    112    @SuppressWarnings("unchecked")
    113    public int compare(final K o1, final K o2) {
    114        if (o1 == null) {
    115            return o2 == null ? 0 : -1;
    116        }
    117        if (o2 == null) {
    118            return 1;
    119        }
    120
    121        return ((Comparable<K>) o1).compareTo(o2);
    122    }
    123
    124    /**
    125     * Returns whether or not a bit is set.
    126     *
    127     * @param key  the key to check, may not be null
    128     * @param bitIndex  the bit index to check
    129     * @param lengthInBits  the maximum key length in bits to check
    130     * @return {@code true} if the bit is set in the given key and
    131     *   {@code bitIndex} &lt; {@code lengthInBits}, {@code false} otherwise.
    132     */
    133    public abstract boolean isBitSet(K key, int bitIndex, int lengthInBits);
    134
    135    /**
    136     * Determines whether or not the given prefix (from offset to length) is a prefix of the given key.
    137     *
    138     * @param prefix  the prefix to check
    139     * @param offsetInBits  the bit offset in the key
    140     * @param lengthInBits  the maximum key length in bits to use
    141     * @param key  the key to check
    142     * @return {@code true} if this is a valid prefix for the given key
    143     */
    144    public abstract boolean isPrefix(K prefix, int offsetInBits, int lengthInBits, K key);
    145
    146    /**
    147     * Returns the length of the Key in bits.
    148     *
    149     * @param key  the key
    150     * @return the bit length of the key
    151     */
    152    public abstract int lengthInBits(K key);
    153
    154}