Toggle String in Java

In this guide, we will learn how to toggle string in Java. Toggle means reversing the case of each character of String (i.e., converting uppercase letters to lowercase and vice versa).

Java Program to Toggle a String

To toggle a given String, you can iterate through each character of String and change its case using toUpperCase() and toLowerCase() methods of Character class. Here is an example of how you can do this:

public class ToggleStringCase {
    public static void main(String[] args) {
        String str = "Hello World!";
        //calling user defined method to toggle string
        String toggled = toggleCase(str);
        System.out.println(toggled);
    }

    public static String toggleCase(String str) {
        StringBuilder toggledStr = new StringBuilder();

        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);

            // if a character is in uppercase, change it to lowercase
            // and if a character is in lowercase, change it to uppercase
            if (Character.isUpperCase(c)) {
                toggledStr.append(Character.toLowerCase(c));
            } else if (Character.isLowerCase(c)) {
                toggledStr.append(Character.toUpperCase(c));
            } else {
                toggledStr.append(c);
            }
        }
        return toggledStr.toString();
    }
}

Output:

hELLO wORLD!

Explanation:

1. Initialization:
   • The str variable contains the string which we want to toggle
   • The toggleCase() method is called with str and its returned value is stored in toggled.
2. toggleCase() Method:
   • In this method we traverse through the whole String using for loop.
   • The case of every character is checked using isUpperCase() and isLowerCase() methods of Character class.
   • If a character is in upper case it is changed to lowercase using toLowerCase() method and if it is in lowercase, it is changed to uppercase using toUpperCase().
3. Output:
   • It prints the string returned by toggleCase() method, which is a toggled string.