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package se.sawano.java.text;
import java.nio.CharBuffer;
import java.text.Collator;
import java.util.Comparator;
import java.util.Locale;
import static java.nio.CharBuffer.wrap;
import static java.util.Objects.requireNonNull;
/**
* An implementation of a comparator that sort strings in an order that makes sense for a human.
*
* This source can be found at https://github.com/sawano/alphanumeric-comparator
*
* Note: this algorithm does not take into account numeric notation such as decimals, negative numbers, scientific notation etc.
*
* @author Daniel Sawano, Copyright 2014
*/
public class AlphanumericComparator implements Comparator {
private final Collator collator;
/**
* Creates a comparator that will use lexicographical sorting of the non-numerical parts of the compared strings.
*/
public AlphanumericComparator() {
collator = null;
}
/**
* Creates a comparator that will use locale-sensitive sorting of the non-numerical parts of the compared strings.
*
* @param locale
* the locale to use
*/
public AlphanumericComparator(final Locale locale) {
this(Collator.getInstance(requireNonNull(locale)));
}
/**
* Creates a comparator that will use the given collator to sort the non-numerical parts of the compared strings.
*
* @param collator
* the collator to use
*/
public AlphanumericComparator(final Collator collator) {
this.collator = requireNonNull(collator);
}
@Override
public int compare(final String s1, final String s2) {
final CharBuffer b1 = wrap(s1);
final CharBuffer b2 = wrap(s2);
while (b1.hasRemaining() && b2.hasRemaining()) {
moveWindow(b1);
moveWindow(b2);
final int result = compare(b1, b2);
if (result != 0) {
return result;
}
prepareForNextIteration(b1);
prepareForNextIteration(b2);
}
return s1.length() - s2.length();
}
private void moveWindow(final CharBuffer buffer) {
int start = buffer.position();
int end = buffer.position();
final boolean isNumerical = isDigit(buffer.get(start));
for (; end < buffer.limit() && isNumerical == isDigit(buffer.get(end)); ++end) {
if (isNumerical && (start + 1 < buffer.limit()) && isZero(buffer.get(start))) {
++start;
}
}
buffer.position(start)
.limit(end);
}
private int compare(final CharBuffer b1, final CharBuffer b2) {
if (isNumerical(b1) && isNumerical(b2)) {
return compareNumerically(b1, b2);
}
return compareAsStrings(b1, b2);
}
private boolean isNumerical(final CharBuffer buffer) {
return isDigit(buffer.charAt(0));
}
private boolean isDigit(final char c) {
if (collator == null) {
final int intValue = (int) c;
return intValue >= 48 && intValue <= 57;
}
return Character.isDigit(c);
}
private int compareNumerically(final CharBuffer b1, final CharBuffer b2) {
final int diff = b1.length() - b2.length();
if (diff != 0) {
return diff;
}
for (int i = 0; i < b1.remaining() && i < b2.remaining(); ++i) {
final int result = Character.compare(b1.charAt(i), b2.charAt(i));
if (result != 0) {
return result;
}
}
return 0;
}
private void prepareForNextIteration(final CharBuffer buffer) {
buffer.position(buffer.limit())
.limit(buffer.capacity());
}
private int compareAsStrings(final CharBuffer b1, final CharBuffer b2) {
if (collator != null) {
return collator.compare(b1.toString(), b2.toString());
}
return b1.toString().compareTo(b2.toString());
}
private boolean isZero(final char c) {
return c == '0';
}
}