Java Program to Convert Lowercase to Uppercase

This post covers a program in Java that converts lowercase characters or strings to uppercase characters or strings with and without using the string function. To achieve this task, we can either use the ASCII values or a string function named toUpperCase().

Lowercase character to uppercase in Java using ASCII

The question is: write a Java program that converts a lowercase character to uppercase using an ASCII value. The character must be received by the user at the runtime of the program. The program given below has its answer:

The ASCII value of 'A' is 65 and 'a' is 97. That is, 97-65 = 32, which indicates that the ASCII value of a lowercase character is 32 more than the ASCII value of an equivalent uppercase character. So to convert a character from lowercase to uppercase, just subtract 32 using ASCII, as shown in the program given below.

import java.util.Scanner;

public class CodesCracker
{
   public static void main(String[] args)
   {
      char ch;
      int ascii;
      Scanner scan = new Scanner(System.in);
      
      System.out.print("Enter a Character in Lowercase: ");
      ch = scan.next().charAt(0);
      
      ascii = ch;
      ascii = ascii - 32;
      ch = (char)ascii;
      
      System.out.println("\nEquivalent Character in Uppercase = " +ch);
   }
}

The snapshot given below shows the sample run of the above Java program, with user input c as a character to convert it to uppercase:

Since the ASCII values of A-Z are 65–90, Whereas the ASCII values of a–z are 97–122. Therefore, as already said, there is a difference of 32 between A and  a, or B and b, and so on. That is, to convert from a to A, we need to subtract 32.

In the above program, the statement:

ascii = ch;

indicates that the value of ch gets initialized to ascii. And because ascii is of the int type, instead of initializing the character itself, its ASCII value gets initialized. That is, the ascii value (99) of 'c' will get initialized to ascii. Now using the statement:

ascii = ascii - 32;

99-32 or 67 will get initialized to ascii. Again, using the statement:

ch = (char)ascii;

In the above statement, the code (char)67 evaluated into the character corresponding to ASCII value 67, that is, C, will get initialized to ch.

Note: I've used char to convert an ASCII value to its equivalent characte before initializing a char-type variable to avoid a loose conversion from int to char. But in case of char to int, we need not to covert manually because of the promotion rules.

The above program can also be created in this way:

import java.util.Scanner;

public class CodesCracker
{
   public static void main(String[] args)
   {
      Scanner scan = new Scanner(System.in);
      
      System.out.print("Enter a Character in Lowercase: ");
      char ch = scan.next().charAt(0);
      
      System.out.println("\nEquivalent Character in Uppercase = " +(char)(ch-32));
   }
}

You'll get the same output as the previous program.

Lowercase Character to Uppercase in Java: Complete Version

Since the program given above has limitations, That limitation is that when the user enters a character already in uppercase, the program in that case too does the process of getting its ASCII value and subtracting by 32, then printing whatever result comes out as an equivalent character in uppercase. That looks weird and is also not a correct program. Therefore, the program needs to be modified. Here is the modified version of the above program:

import java.util.Scanner;

public class CodesCracker
{
   public static void main(String[] args)
   {
      Scanner scan = new Scanner(System.in);
      
      System.out.print("Enter an Alphabet: ");
      char ch = scan.next().charAt(0);
      
      int ascii = ch;
      if(ascii>=97 && ascii<=122)
      {
         ascii = ascii - 32;
         ch = (char)ascii;
         System.out.println("\nEquivalent Character in Uppercase = " +ch);
      }
      else if(ascii>=65 && ascii<=90)
         System.out.println("\nThe alphabet is already in Uppercase");
      else
         System.out.println("\nIt is not an alphabet");
      
   }
}

The sample run of the above program with user input R:

Here is another sample run with user input $ (not an alphabet input):

Lowercase String to Uppercase in Java without using the String Function

This program converts a lowercase string to an uppercase string without using the string function toUpperCase().

import java.util.Scanner;

public class CodesCracker
{
   public static void main(String[] args)
   {
      String str;
      int len, i, ascii;
      char ch;
      Scanner scan = new Scanner(System.in);
      
      System.out.print("Enter the String: ");
      str = scan.nextLine();
      
      len = str.length();
      char[] strChars = new char[len];
      char[] strUpperChars = new char[len];
      for(i=0; i<len; i++)
         strChars[i] = str.charAt(i);
 
      for(i=0; i<len; i++)
      {
         ch = strChars[i];
         ascii = ch;
         if(ascii>=97 && ascii<=122)
         {
            ascii = ascii - 32;
            ch = (char)ascii;
            strUpperChars[i] = ch;
         }
         else
            strUpperChars[i] = ch;
      }
      
      System.out.print("\nString in Uppercase: ");
      for(i=0; i<len; i++)
         System.out.print(strUpperChars[i]);
   }
}

Here is its sample run with user input cOdesCRAcker dOt cOm @098 as a string. I've supplied both lowercase and uppercase alphabets, along with some other characters:

In the above program, the entered string stored in str gets initialized to a character array, strChars, in a character-by-character manner. And further, each and every lowercase alphabet of this character array gets capitalized and initialized to another character array named strUpperChars. Finally, I've printed the value of strUpperChars, character-by-character.

Lowercase String to Uppercase in Java using the String Function

This is the last program in this post, created using a string function to convert lowercase strings to uppercase directly.

import java.util.Scanner;

public class CodesCracker
{
   public static void main(String[] args)
   {
      String str;
      Scanner scan = new Scanner(System.in);
      
      System.out.print("Enter the String: ");
      str = scan.nextLine();
      
      str = str.toUpperCase();
      System.out.println("\nEquivalent String in Uppercase = " +str);
   }
}

The sample run of the above program with user input CodesCracker doT cOm 100 as a string:

Same Program in Other Languages

• C Convert Lowercase to Uppercase
• C++ Convert Lowercase to Uppercase
• Python Convert Lowercase to Uppercase

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