Comparator similar to String.CASE_INSENSITIVE_ORDER, but handles only ASCII characters : Comparator « Collections Data Structure « Java

Comparator similar to String.CASE_INSENSITIVE_ORDER, but handles only ASCII characters

 * Copyright 2006-2007 The Scriptella Project Team.
 * Licensed 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
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.

import java.util.Comparator;
import java.util.Map;
import java.util.Properties;
import java.util.TreeMap;

 * Collections utility methods.
 * @author Fyodor Kupolov
 * @version 1.0
public final class CollectionUtils {
    private CollectionUtils() {//Singleton

     * Comparator similar to {@link String#CASE_INSENSITIVE_ORDER}, but
     * handles only ASCII characters
    private static final Comparator<String> ASCII_CASE_INSENSITIVE_ORDER = new Comparator<String>() {
        public int compare(String s1, String s2) {
            int n1 = s1.length(), n2 = s2.length();
            int n = n1 < n2 ? n1 : n2;
            for (int i = 0; i < n; i++) {
                char c1 = s1.charAt(i);
                char c2 = s2.charAt(i);
                if (c1 != c2) {
                    if (c1 >= 'A' && c1 <= 'Z') { //Fast lower case
                        c1 = (char) (c1 | 0x20);
                    if (c2 >= 'A' && c2 <= 'Z') {
                        c2 = (char) (c2 | 0x20);
                    if (c1 != c2) {
                        return c1 - c2;
            return n1 - n2;

     * Create a map optimized for case insensitive search for keys.
     * The case insensitive rules are simplified to ASCII chars for performance reasons.
     * @return case insensitive map.
    public static <V> Map<String, V> newCaseInsensitiveAsciiMap() {
        return new TreeMap<String, V>(ASCII_CASE_INSENSITIVE_ORDER);

     * Returns parameterized version of {@link Properties} the instance
     * remains the same.
     * @param properties properties to represent as a map.
    public static Map<String, String> asMap(Properties properties) {
        return (Map) properties;

     * Converts specified map to {@link java.util.Properties}. The keys and String values
     * are migrated unchnaged, other types of values are {@link Object#toString() converted to String}.
     * @param map map to convert.
     * @return converted map as Properties.
    public static Properties asProperties(Map<String, ?> map) {
        Properties props = new Properties();
        for (Map.Entry<String, ?> entry : map.entrySet()) {
            Object v = entry.getValue();
            if (v != null) {
                props.put(entry.getKey(), v.toString());
        return props;



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