Java String Case Swap swapCase(String str)

Description

Swaps the case of a String using a word based algorithm.

• Upper case character converts to Lower case
• Title case character converts to Lower case
• Lower case character after Whitespace or at start converts to Title case
• Other Lower case character converts to Upper case

Whitespace is defined by Character#isWhitespace(char) .

License

Apache License

Parameter

Parameter	Description
str	the String to swap case, may be null

Return

the changed String, null if null String input

Declaration

public static String swapCase(String str) 

Method Source Code

//package com.java2s;
/*// www .  j a  v  a2s .  c  om
 * 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.
 */

public class Main {
    /**
     * <p>Swaps the case of a String using a word based algorithm.</p>
     * 
     * <ul>
     *  <li>Upper case character converts to Lower case</li>
     *  <li>Title case character converts to Lower case</li>
     *  <li>Lower case character after Whitespace or at start converts to Title case</li>
     *  <li>Other Lower case character converts to Upper case</li>
     * </ul>
     * 
     * <p>Whitespace is defined by {@link Character#isWhitespace(char)}.
     * A <code>null</code> input String returns <code>null</code>.</p>
     * 
     * <pre>
     * StringUtils.swapCase(null)                 = null
     * StringUtils.swapCase("")                   = ""
     * StringUtils.swapCase("The dog has a BONE") = "tHE DOG HAS A bone"
     * </pre>
     * 
     * @param str  the String to swap case, may be null
     * @return the changed String, <code>null</code> if null String input
     */
    public static String swapCase(String str) {
        char[] buffer = str.toCharArray();

        boolean whitespace = true;

        for (int i = 0; i < buffer.length; i++) {
            char ch = buffer[i];
            if (Character.isUpperCase(ch)) {
                buffer[i] = Character.toLowerCase(ch);
                whitespace = false;
            } else if (Character.isTitleCase(ch)) {
                buffer[i] = Character.toLowerCase(ch);
                whitespace = false;
            } else if (Character.isLowerCase(ch)) {
                if (whitespace) {
                    buffer[i] = Character.toTitleCase(ch);
                    whitespace = false;
                } else {
                    buffer[i] = Character.toUpperCase(ch);
                }
            } else {
                whitespace = Character.isWhitespace(ch);
            }
        }
        return new String(buffer);
    }
}

Related

1. swapCase(String str)
2. swapCase(String str)
3. swapCase(String str)
4. swapCase(String str)
5. swapCase(String str)
6. swapFirstLetterCase(String str)