Java - Write code to swap String Case via Character helper method

Requirements

Write code to swap Case

Demo

//package com.book2s;

public class Main {
    public static void main(String[] argv) {
        String str = "book2s.com";
        System.out.println(swapCase(str));
    }//from  ww w .  ja v  a2s. c om

    public static String swapCase(String str) {
        int strLen;

        if ((str == null) || ((strLen = str.length()) == 0)) {
            return str;
        }

        StringBuffer buffer = new StringBuffer(strLen);

        char ch = 0;

        for (int i = 0; i < strLen; i++) {
            ch = str.charAt(i);

            if (Character.isUpperCase(ch)) {
                ch = Character.toLowerCase(ch);
            } else if (Character.isTitleCase(ch)) {
                ch = Character.toLowerCase(ch);
            } else if (Character.isLowerCase(ch)) {
                ch = Character.toUpperCase(ch);
            }

            buffer.append(ch);
        }

        return buffer.toString();
    }

}