Convert a String to Uppercase and Lowercase in Java

Conversion Programs

Topic: Convert a String to Uppercase and Lowercase

In this Java interview program, you'll learn how to convert a string to uppercase and lowercase using simple built-in methods. This is a basic string manipulation task often asked to assess familiarity with the String class and method usage.

Java provides two useful methods for this:

  • toUpperCase(): Converts all characters to uppercase.
  • toLowerCase(): Converts all characters to lowercase.

Examples

  • Input: "Hello World" → Uppercase: "HELLO WORLD", Lowercase: "hello world"
  • Input: "Java123" → Uppercase: "JAVA123", Lowercase: "java123"
  • Edge Case Input: "" → Uppercase: "", Lowercase: ""

Note that numbers and symbols remain unchanged during case conversion.

Interviewer Expectations

The interviewer is checking whether the candidate:

  • Understands how to manipulate strings in Java.
  • Is familiar with Java’s built-in String methods.
  • Can write a clean and simple program using standard Java syntax.

Approach

The solution is straightforward and ideal for beginners:

  1. Accept a string (hardcoded or user input).
  2. Use toUpperCase() and toLowerCase() methods to transform the string.
  3. Print the converted results.

Dry Run

Let's take the input "Welcome123":

  • Uppercase: "WELCOME123"
  • Lowercase: "welcome123"

Java Program

public class CaseConverter {
    public static void main(String[] args) {
        String originalText = "Hello Java 123!";
        String upperText = originalText.toUpperCase();
        String lowerText = originalText.toLowerCase();

        System.out.println("Uppercase: " + upperText);
        System.out.println("Lowercase: " + lowerText);
    }
}
Uppercase: HELLO JAVA 123!
Lowercase: hello java 123!

Possible Followup Questions with Answers

Q1. What happens if the string is already in uppercase?

Answer: Nothing changes. The toUpperCase() method will return the same string as input.

Q2. Do these methods modify the original string?

Answer: No. String in Java is immutable. These methods return new string objects.

Q3. How do you handle user input instead of hardcoded strings?

Scanner sc = new Scanner(System.in);
System.out.print("Enter a string: ");
String input = sc.nextLine();
System.out.println(input.toUpperCase());
System.out.println(input.toLowerCase());

Q4. How would you convert only the first letter to uppercase?

String input = "java";
String result = input.substring(0, 1).toUpperCase() + input.substring(1).toLowerCase();
System.out.println(result); // Output: Java

Comments

💬 Please keep your comment relevant and respectful. Avoid spamming, offensive language, or posting promotional/backlink content.
All comments are subject to moderation before being published.

Loading comments...

Conversion Programs❯

  1. 1Convert Decimal to Binary in Java
  2. 2Convert Binary to Decimal in Java
  3. 3Convert Decimal to Octal in Java
  4. 4Convert Octal to Decimal in Java
  5. 5Convert Decimal to Hexadecimal in Java
  6. 6Convert Hexadecimal to Decimal in Java
  7. 7Convert Binary to Hexadecimal in Java
  8. 8Convert Hexadecimal to Binary in Java
  9. 9Convert Octal to Binary in Java
  10. 10Convert Temperature from Celsius to Fahrenheit in Java
  11. 11Convert Kilometers to Miles, Meters, and Centimeters in Java
  12. 12Convert a String to Uppercase and Lowercase in Java