Toggle Case

/*
 * Problem : Process one line of text.
 * Input   : One line of text.
 * Output  : Swap the case.
 * Approach: Test each character.
 * Time    : O(n)
 * Space   : O(n)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static String solve(String s) {
        // Step 1: Build the answer in a StringBuilder.
        StringBuilder result = new StringBuilder();

        // Step 2: Look at every character.
        for (char c : s.toCharArray()) {
            // Step 3: Upper case becomes lower case, lower case becomes upper case, others stay.
            if (Character.isUpperCase(c)) {
                result.append(Character.toLowerCase(c));
            } else if (Character.isLowerCase(c)) {
                result.append(Character.toUpperCase(c));
            } else {
                result.append(c);
            }
        }
        return result.toString();
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String s = scanner.hasNextLine() ? scanner.nextLine() : "";
        System.out.println(solve(s));
    }
}