Java - Write code to swap Case

Requirements

Write code to swap Case

Demo

import java.util.ArrayList;
import java.util.List;

public class Main{
    public static void main(String[] argv){
        String str = "book2s.com";
        System.out.println(swapCase(str));
    }//from ww  w  .j  a v a 2 s  .  co m
    
    public static String swapCase(String str) {
        if (isEmpty(str)) {
            return 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);
    }
    
    public static boolean isEmpty(String chkStr) {
        if (chkStr == null) {
            return true;
        } else {
            return "".equals(chkStr.trim()) ? true : false;
        }
    }
}