Java String Case Converter

import java.util.*;

class StringExample {
        public static void main(String[] args) {
                Scanner input = new Scanner(System.in);
                System.out.print("Enter string: ");
                String str = input.nextLine();
                StringBuffer sb = new StringBuffer();
                char ch[] = str.toCharArray();
                for (int i = 0; i < ch.length; i++) {
                        if (ch[i] == ' ') {
                                sb.append(" ");
                        }
                        if (Character.isLowerCase(ch[i])) {
                                char cha = Character.toUpperCase(ch[i]);
                                sb.append(Character.toString(cha));
                        } else if (Character.isUpperCase(ch[i])) {
                                char cha = Character.toLowerCase(ch[i]);
                                sb.append(Character.toString(cha));
                        }
                }
                System.out.println(sb.toString() + " ");
        }
}