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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.collections4.trie;
import java.io.Serializable;
import java.util.Comparator;
/**
* Defines the interface to analyze {@link org.apache.commons.collections4.Trie Trie} keys on a bit level.
* {@link KeyAnalyzer}'s methods return the length of the key in bits, whether or not a bit is set,
* and bits per element in the key.
*
* Additionally, a method determines if a key is a prefix of another
* key and returns the bit index where one key is different from another
* key (if the key and found key are equal than the return value is
* {@link #EQUAL_BIT_KEY}).
*
* @param the type of objects that may be compared by this analyzer
* @since 4.0
*/
public abstract class KeyAnalyzer implements Comparator, Serializable {
/** Serialization version */
private static final long serialVersionUID = -20497563720380683L;
/**
* Returned by {@link #bitIndex(Object, int, int, Object, int, int)}
* if key's bits are all 0.
*/
public static final int NULL_BIT_KEY = -1;
/**
* Returned by {@link #bitIndex(Object, int, int, Object, int, int)} if key and found key are equal.
* This is a very very specific case and shouldn't happen on a regular basis.
*/
public static final int EQUAL_BIT_KEY = -2;
public static final int OUT_OF_BOUNDS_BIT_KEY = -3;
/**
* Returns true if bitIndex is a {@link KeyAnalyzer#OUT_OF_BOUNDS_BIT_KEY}.
*/
static boolean isOutOfBoundsIndex(final int bitIndex) {
return bitIndex == OUT_OF_BOUNDS_BIT_KEY;
}
/**
* Returns true if bitIndex is a {@link KeyAnalyzer#EQUAL_BIT_KEY}.
*/
static boolean isEqualBitKey(final int bitIndex) {
return bitIndex == EQUAL_BIT_KEY;
}
/**
* Returns true if bitIndex is a {@link KeyAnalyzer#NULL_BIT_KEY}.
*/
static boolean isNullBitKey(final int bitIndex) {
return bitIndex == NULL_BIT_KEY;
}
/**
* Returns true if the given bitIndex is valid.
* Indices are considered valid if they're between 0 and {@link Integer#MAX_VALUE}
*/
static boolean isValidBitIndex(final int bitIndex) {
return bitIndex >= 0;
}
/**
* Returns the number of bits per element in the key.
* This is only useful for variable-length keys, such as Strings.
*
* @return the number of bits per element
*/
public abstract int bitsPerElement();
/**
* Returns the length of the Key in bits.
*
* @param key the key
* @return the bit length of the key
*/
public abstract int lengthInBits(K key);
/**
* Returns whether or not a bit is set.
*
* @param key the key to check, may not be null
* @param bitIndex the bit index to check
* @param lengthInBits the maximum key length in bits to check
* @return {@code true} if the bit is set in the given key and
* {@code bitIndex} < {@code lengthInBits}, {@code false} otherwise.
*/
public abstract boolean isBitSet(K key, int bitIndex, int lengthInBits);
/**
* Returns the n-th different bit between key and other. This starts the comparison in
* key at 'offsetInBits' and goes for 'lengthInBits' bits, and compares to the other key starting
* at 'otherOffsetInBits' and going for 'otherLengthInBits' bits.
*
* @param key the key to use
* @param offsetInBits the bit offset in the key
* @param lengthInBits the maximum key length in bits to use
* @param other the other key to use
* @param otherOffsetInBits the bit offset in the other key
* @param otherLengthInBits the maximum key length in bits for the other key
* @return the bit index where the key and other first differ
*/
public abstract int bitIndex(K key, int offsetInBits, int lengthInBits,
K other, int otherOffsetInBits, int otherLengthInBits);
/**
* Determines whether or not the given prefix (from offset to length) is a prefix of the given key.
*
* @param prefix the prefix to check
* @param offsetInBits the bit offset in the key
* @param lengthInBits the maximum key length in bits to use
* @param key the key to check
* @return {@code true} if this is a valid prefix for the given key
*/
public abstract boolean isPrefix(K prefix, int offsetInBits, int lengthInBits, K key);
@Override
@SuppressWarnings("unchecked")
public int compare(final K o1, final K o2) {
if (o1 == null) {
return o2 == null ? 0 : -1;
} else if (o2 == null) {
return 1;
}
return ((Comparable) o1).compareTo(o2);
}
}