/**
* 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.avro.hadoop.util;
import java.util.Comparator;
/**
* Compares Avro string data (data with schema <i>"string"</i>).
*
* <p>The only case where comparing Avro objects does not work using their natural order
* is when the schema is <i>"string"</i>. The Avro string schema maps to the Java
* <code>CharSequence</code> interface, which does not define <code>equals</code>,
* <code>hashCode</code>, or <code>compareTo</code>.</p>
*
* <p>Using this comparator enables comparisons between <code>String</code> and
* <code>Utf8</code> objects that are both valid when working with Avro strings.</p>
*
* @param <T> The type of object to compare.
*/
public class AvroCharSequenceComparator<T> implements Comparator<T> {
/** A singleton instance. */
public static final AvroCharSequenceComparator<CharSequence> INSTANCE
= new AvroCharSequenceComparator<CharSequence>();
/** {@inheritDoc} */
@Override
public int compare(T o1, T o2) {
if (!(o1 instanceof CharSequence) || !(o2 instanceof CharSequence)) {
throw new RuntimeException(
"Attempted use of AvroCharSequenceComparator on non-CharSequence objects: "
+ o1.getClass().getName() + " and " + o2.getClass().getName());
}
return compareCharSequence((CharSequence) o1, (CharSequence) o2);
}
/**
* Compares the CharSequences <code>o1</code> and <code>o2</code>.
*
* @param o1 The left charsequence.
* @param o2 The right charsequence.
* @return a negative integer, zero, or a positive integer if the first argument is
* less than, equal to, or greater than the second, respectively.
*/
private int compareCharSequence(CharSequence o1, CharSequence o2) {
for (int i = 0; i < Math.max(o1.length(), o2.length()); i++) {
int charComparison = compareCharacter(o1, o2, i);
if (0 != charComparison) {
return charComparison;
}
}
return 0;
}
/**
* Compares the characters of <code>o1</code> and <code>o2</code> at index <code>index</code>.
*
* @param o1 The left charsequence.
* @param o2 The right charsequence.
* @param index The zero-based index into the charsequences to compare.
* @return a negative integer, zero, or a positive integer if the first argument is
* less than, equal to, or greater than the second, respectively.
*/
private int compareCharacter(CharSequence o1, CharSequence o2, int index) {
if (index < o1.length() && index < o2.length()) {
return Character.valueOf(o1.charAt(index)).compareTo(Character.valueOf(o2.charAt(index)));
}
if (index >= o1.length() && index >= o2.length()) {
return 0;
}
return o1.length() - o2.length();
}
}