Convert String to Lowercase in Java Without Using String Library

Convert String to Lowercase in Java Without Using String Library

Converting a string to lowercase without using built-in String methods helps beginners understand how characters are represented internally and how ASCII values work.

In this blog, you will learn:

• How uppercase and lowercase characters are stored
• ASCII value logic for case conversion
• Step-by-step examples
• A Java program without using String library methods
• Practice challenges

Understanding ASCII Values

In ASCII:

• Uppercase letters ('A' to 'Z') → 65 to 90
• Lowercase letters ('a' to 'z') → 97 to 122

The difference between uppercase and lowercase letters is 32.

How the Logic Works

To convert a string to lowercase manually:

1. Traverse each character of the string.
2. If the character is between 'A' and 'Z', add 32.
3. Leave other characters unchanged.

Example

Input: "Java PROGRAMMING 101"

• 'J' → 'j'
• 'P' → 'p'
• '101' → unchanged

Output: "java programming 101"

Java Program to Convert String to Lowercase

import java.util.Scanner;

public class StringToLowercase {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        System.out.print("Enter a string: ");
        String input = sc.nextLine();

        String result = "";

        for (int i = 0; i < input.length(); i++) {
            char ch = input.charAt(i);

            if (ch >= 'A' && ch <= 'Z') {
                ch = (char) (ch + 32);
            }

            result = result + ch;
        }

        System.out.println("Lowercase String: " + result);
    }
}

Sample Output

Enter a string: HELLO World
Lowercase String: hello world

Practice Challenges

1. Convert a string to uppercase without using String library methods.
2. Toggle the case of each character in a string.
3. Count uppercase and lowercase characters in a string.

Manual case conversion builds a strong foundation in character handling and ASCII logic. These concepts are commonly tested in interviews and competitive programming.