framework/src/main/java/org/apache/felix/framework/util/StringComparator.java

/*
 * 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.felix.framework.util;

import java.util.Comparator;

public class StringComparator implements Comparator<String>
{

    public static final StringComparator COMPARATOR = new StringComparator();

    public int compare(String s1, String s2)
    {
        int n1 = s1.length();
        int n2 = s2.length();
        int min = n1 < n2 ? n1 : n2;
        for ( int i = 0; i < min; i++ )
        {
            char c1 = s1.charAt( i );
            char c2 = s2.charAt( i );
            if ( c1 != c2 )
            {
                // Fast check for simple ascii codes
                if ( c1 <= 128 && c2 <= 128 )
                {
                    c1 = toLowerCaseFast(c1);
                    c2 = toLowerCaseFast(c2);
                    if ( c1 != c2 )
                    {
                        return c1 - c2;
                    }
                }
                else
                {
                    c1 = Character.toUpperCase( c1 );
                    c2 = Character.toUpperCase( c2 );
                    if ( c1 != c2 )
                    {
                        c1 = Character.toLowerCase( c1 );
                        c2 = Character.toLowerCase( c2 );
                        if ( c1 != c2 )
                        {
                            // No overflow because of numeric promotion
                            return c1 - c2;
                        }
                    }
                }
            }
        }
        return n1 - n2;
    }

    private static char toLowerCaseFast( char ch )
    {
        return ( ch >= 'A' && ch <= 'Z' ) ? ( char ) ( ch + 'a' - 'A' ) : ch;
    }
}