    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 *      https://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
    022import org.apache.commons.collections4.Trie;
    023
    024/**
    025 * Defines the interface to analyze {@link Trie Trie} keys on a bit level.
    026 * {@link KeyAnalyzer}'s methods return the length of the key in bits, whether or not a bit is set,
    027 * and bits per element in the key.
    028 * <p>
    029 * Additionally, a method determines if a key is a prefix of another
    030 * key and returns the bit index where one key is different from another
    031 * key (if the key and found key are equal than the return value is
    032 * {@link #EQUAL_BIT_KEY}).
    033 * </p>
    034 *
    035 * @param <K> The type of objects that may be compared by this analyzer
    036 * @since 4.0
    037 */
    038public abstract class KeyAnalyzer<K> implements Comparator<K>, Serializable {
    039
    040    /** Serialization version */
    041    private static final long serialVersionUID = -20497563720380683L;
    042
    043    /**
    044     * Returned by {@link #bitIndex(Object, int, int, Object, int, int)}
    045     * if key's bits are all 0.
    046     */
    047    public static final int NULL_BIT_KEY = -1;
    048
    049    /**
    050     * Returned by {@link #bitIndex(Object, int, int, Object, int, int)} if key and found key are equal.
    051     * This is a very specific case and shouldn't happen on a regular basis.
    052     */
    053    public static final int EQUAL_BIT_KEY = -2;
    054
    055    /**
    056     * Used to test a {@code bitIndex} in {@link #isOutOfBoundsIndex(int)}.
    057     */
    058    public static final int OUT_OF_BOUNDS_BIT_KEY = -3;
    059
    060    /**
    061     * Returns true if bitIndex is a {@link KeyAnalyzer#EQUAL_BIT_KEY}.
    062     */
    063    static boolean isEqualBitKey(final int bitIndex) {
    064        return bitIndex == EQUAL_BIT_KEY;
    065    }
    066
    067    /**
    068     * Returns true if bitIndex is a {@link KeyAnalyzer#NULL_BIT_KEY}.
    069     */
    070    static boolean isNullBitKey(final int bitIndex) {
    071        return bitIndex == NULL_BIT_KEY;
    072    }
    073
    074    /**
    075     * Returns true if bitIndex is a {@link KeyAnalyzer#OUT_OF_BOUNDS_BIT_KEY}.
    076     */
    077    static boolean isOutOfBoundsIndex(final int bitIndex) {
    078        return bitIndex == OUT_OF_BOUNDS_BIT_KEY;
    079    }
    080
    081    /**
    082     * Returns true if the given bitIndex is valid.
    083     * Indices are considered valid if they're between 0 and {@link Integer#MAX_VALUE}
    084     */
    085    static boolean isValidBitIndex(final int bitIndex) {
    086        return bitIndex >= 0;
    087    }
    088
    089    /**
    090     * Constructs a new instance.
    091     */
    092    public KeyAnalyzer() {
    093        // empty
    094    }
    095
    096    /**
    097     * Returns the n-th different bit between key and other. This starts the comparison in
    098     * key at 'offsetInBits' and goes for 'lengthInBits' bits, and compares to the other key starting
    099     * at 'otherOffsetInBits' and going for 'otherLengthInBits' bits.
    100     *
    101     * @param key  The key to use
    102     * @param offsetInBits  The bit offset in the key
    103     * @param lengthInBits  The maximum key length in bits to use
    104     * @param other  The other key to use
    105     * @param otherOffsetInBits  The bit offset in the other key
    106     * @param otherLengthInBits  The maximum key length in bits for the other key
    107     * @return The bit index where the key and other first differ
    108     */
    109    public abstract int bitIndex(K key, int offsetInBits, int lengthInBits,
    110                                 K other, int otherOffsetInBits, int otherLengthInBits);
    111
    112    /**
    113     * Returns the number of bits per element in the key.
    114     * This is only useful for variable-length keys, such as Strings.
    115     *
    116     * @return The number of bits per element
    117     */
    118    public abstract int bitsPerElement();
    119
    120    @Override
    121    @SuppressWarnings("unchecked")
    122    public int compare(final K o1, final K o2) {
    123        if (o1 == null) {
    124            return o2 == null ? 0 : -1;
    125        }
    126        if (o2 == null) {
    127            return 1;
    128        }
    129
    130        return ((Comparable<K>) o1).compareTo(o2);
    131    }
    132
    133    /**
    134     * Returns whether or not a bit is set.
    135     *
    136     * @param key  The key to check, may not be null
    137     * @param bitIndex  The bit index to check
    138     * @param lengthInBits  The maximum key length in bits to check
    139     * @return {@code true} if the bit is set in the given key and
    140     *   {@code bitIndex} &lt; {@code lengthInBits}, {@code false} otherwise.
    141     */
    142    public abstract boolean isBitSet(K key, int bitIndex, int lengthInBits);
    143
    144    /**
    145     * Determines whether or not the given prefix (from offset to length) is a prefix of the given key.
    146     *
    147     * @param prefix  The prefix to check
    148     * @param offsetInBits  The bit offset in the key
    149     * @param lengthInBits  The maximum key length in bits to use
    150     * @param key  The key to check
    151     * @return {@code true} if this is a valid prefix for the given key
    152     */
    153    public abstract boolean isPrefix(K prefix, int offsetInBits, int lengthInBits, K key);
    154
    155    /**
    156     * Returns the length of the Key in bits.
    157     *
    158     * @param key  The key
    159     * @return The bit length of the key
    160     */
    161    public abstract int lengthInBits(K key);
    162
    163}