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ASCII Value of a Character

Java coding interview problem for Character Problems: ASCII Value of a Character.

Finding the ASCII value of a character is one of the most fundamental Java interview questions.

Although it looks very simple, it tests your understanding of:

  • Character Encoding
  • ASCII
  • Unicode
  • Type Casting
  • Primitive Data Types
  • Character APIs
  • Memory Representation

Many advanced String algorithms internally depend on ASCII or Unicode values.

Examples include:

  • Toggle Case
  • Character Frequency
  • Caesar Cipher
  • Encryption
  • Compression Algorithms
  • Lexicographical Comparison

Understanding ASCII makes many String interview questions much easier.

What is ASCII?

ASCII stands for

American Standard Code for Information Interchange

It is a character encoding standard that assigns a unique numeric value to every English letter, digit, and special symbol.

Instead of storing

A

the computer stores

65

Instead of storing

a

the computer stores

97

Computers process numbers internally.

ASCII provides a mapping between characters and numbers.

History of ASCII

ASCII was introduced in

1963

by the

American National Standards Institute (ANSI)

Its purpose was to create a common standard for communication between computers.

Originally,

ASCII defined

128 Characters

Numbered

0

↓

127

These include

  • English Letters
  • Digits
  • Symbols
  • Control Characters

Later,

Unicode extended ASCII to support almost every language in the world.

Why is this Question Asked in Interviews?

Interviewers ask this question to evaluate:

  • Character Encoding Knowledge
  • Primitive Type Conversion
  • Type Casting
  • Unicode Basics
  • Character Manipulation
  • Java Internals

Although easy,

it serves as the foundation for many advanced String problems.

Real-World Applications

ASCII values are used in many applications.

Encryption

Caesar Cipher

A

↓

65

Shift

+3

Result

68

↓

D

Password Validation

Determine

  • Uppercase
  • Lowercase
  • Digits

using ASCII ranges.

Character Sorting

Lexicographical comparison depends on character values.

Networking

Protocols often transmit bytes representing ASCII values.

File Formats

Text files internally store characters using ASCII or Unicode encoding.

Compiler Design

Compilers identify

  • Letters
  • Digits
  • Operators

using character codes.

Problem Statement

Given a character,

print its corresponding ASCII value.

Example 1

Input

A

Output

65

Example 2

Input

a

Output

97

Example 3

Input

1

Output

49

Example 4

Input

@

Output

64

ASCII Table

Uppercase Letters

Character ASCII
A 65
B 66
C 67
D 68
E 69
F 70
... ...
Z 90

Lowercase Letters

Character ASCII
a 97
b 98
c 99
d 100
e 101
... ...
z 122

Digits

Character ASCII
0 48
1 49
2 50
3 51
4 52
5 53
6 54
7 55
8 56
9 57

Common Special Characters

Character ASCII
Space 32
! 33
" 34
# 35
$ 36
% 37
& 38
' 39
( 40
) 41
* 42
+ 43
, 44
- 45
. 46
/ 47
: 58
; 59
< 60
= 61
> 62
? 63
@ 64

Understanding Character Encoding

Suppose we have

A

Computer stores

65

Character

B

Stored as

66

Character

a

Stored as

97

Character

1

Stored as

49

Everything inside the computer is ultimately represented as numbers.

ASCII Visualization

Character

A

↓

65

Character

Z

↓

90

Character

a

↓

97

Character

0

↓

48

Character

@

↓

64

Mathematical Concept

Uppercase letters

A

↓

65

B

↓

66

Difference

1

Lowercase letters

a

↓

97

b

↓

98

Difference

1

Digits

0

↓

48

9

↓

57

Range

48

↓

57

Dry Run

Input

C

Read

Character

↓

C

Type Cast

(int)'C'

Result

67

Output

67

Input

9

Cast

(int)'9'

Output

57

Approach 1 — Using Type Casting (Recommended)

Every char in Java internally stores a numeric Unicode value.

For ASCII characters,

this numeric value is identical to the ASCII code.

We can obtain it simply by casting the character to an int.

Algorithm

  1. Read the character.
  2. Cast it to int.
  3. Print the numeric value.

Java Program

public class ASCIIValueUsingCasting {

    public static void main(String[] args) {

        char ch = 'A';

        int ascii = (int) ch;

        System.out.println("Character : " + ch);
        System.out.println("ASCII Value : " + ascii);

    }

}

Output

Character : A

ASCII Value : 65

Step-by-Step Code Explanation

Declare a character.

char ch = 'A';

Convert it into an integer.

int ascii = (int) ch;

Print the result.

System.out.println(ascii);

The cast returns the Unicode code point for the character. For standard ASCII characters (0–127), this value matches the ASCII code exactly.

Dry Run of Type Casting

Input

B

Cast

(int)'B'

Result

66

Print

ASCII Value = 66

Advantages

  • Simplest solution.
  • Fastest approach.
  • No additional methods required.
  • Preferred interview solution.
  • Constant time complexity.

Drawbacks

  • Beginners may not understand type casting initially.
  • Returns the Unicode code point for non-ASCII characters, not an ASCII value.

Approach 2 — Using Character.codePointAt()

The Character class provides methods to work with Unicode code points.

Although primarily designed for Unicode,

it also works for ASCII characters.

Algorithm

  1. Store the character in a string.
  2. Call codePointAt(0).
  3. Print the returned value.

Java Program

public class ASCIIUsingCodePoint {

    public static void main(String[] args) {

        String text = "A";

        int ascii = text.codePointAt(0);

        System.out.println("Character : " + text.charAt(0));
        System.out.println("ASCII Value : " + ascii);

    }

}

Output

Character : A

ASCII Value : 65

Step-by-Step Code Explanation

Create a string.

String text = "A";

Read the Unicode code point.

text.codePointAt(0);

Store the result.

int ascii = text.codePointAt(0);

Print the value.

System.out.println(ascii);

Time & Space Complexity

Approach Time Extra Space
Type Casting O(1) O(1)
codePointAt() O(1) O(1)

Comparison of Approaches

Feature Type Casting codePointAt()
Interview Friendly ⭐⭐⭐⭐⭐ ⭐⭐⭐⭐
Performance ⭐⭐⭐⭐⭐ ⭐⭐⭐⭐⭐
Easy to Understand ⭐⭐⭐⭐⭐ ⭐⭐⭐⭐
Supports Unicode ✅ ✅
Best Use Case Single Character Strings & Unicode

Advantages

  • Both approaches run in O(1) time.
  • Both work for ASCII characters.
  • Both also return Unicode code points for non-ASCII characters.
  • Type Casting is the simplest interview solution.

Drawbacks

  • Neither approach validates whether the character belongs to the ASCII range.
  • codePointAt() requires a String and is slightly more verbose.

Approach 3 — Using Integer.valueOf()

Java automatically converts a char to its corresponding integer value.

We can use Integer.valueOf() after casting the character to an integer.

Although this approach is less common, it demonstrates Java wrapper class usage.

Algorithm

  1. Read a character.
  2. Cast it to an integer.
  3. Pass it to Integer.valueOf().
  4. Print the value.

Java Program

public class ASCIIUsingIntegerValueOf {

    public static void main(String[] args) {

        char ch = 'A';

        Integer ascii = Integer.valueOf((int) ch);

        System.out.println("Character : " + ch);
        System.out.println("ASCII Value : " + ascii);

    }

}

Output

Character : A

ASCII Value : 65

Advantages

  • Demonstrates Wrapper Classes.
  • Useful when Integer objects are required.
  • Easy to understand.

Drawbacks

  • Extra object creation.
  • No advantage over simple casting.
  • Rarely used in interviews.

Approach 4 — Using Unicode Code Point APIs

Java internally uses Unicode rather than ASCII.

The Character class provides APIs for working with Unicode code points.

These APIs are especially useful when handling multilingual text.

Why Unicode APIs?

ASCII supports only

128 Characters

Unicode supports

Millions of Characters

including

English

Hindi

Chinese

Japanese

Emoji

Java Program

public class UnicodeCodePointExample {

    public static void main(String[] args) {

        char ch = 'A';

        int codePoint = Character.codePointAt(
                new char[]{ch}, 0);

        System.out.println("Character : " + ch);
        System.out.println("Code Point : " + codePoint);

    }

}

Output

Character : A

Code Point : 65

Advantages

  • Unicode-aware.
  • Production-ready.
  • Handles international text.

Drawbacks

  • Slightly more verbose.
  • Overkill for ASCII-only problems.

Approach 5 — Display ASCII Table Programmatically

Sometimes interviewers ask:

"Can you print the entire ASCII table?"

This is a common follow-up question.

Algorithm

  1. Iterate from 0 to 127.
  2. Convert each integer into a character.
  3. Print both values.

Java Program

public class PrintASCIITable {

    public static void main(String[] args) {

        System.out.printf("%-10s %-10s%n",
                "ASCII", "Character");

        for (int i = 0; i <= 127; i++) {

            System.out.printf("%-10d %-10c%n",
                    i, (char) i);

        }

    }

}

Sample Output

ASCII      Character

65         A

66         B

67         C

68         D

69         E

...

97         a

98         b

99         c

Advantages

  • Demonstrates loops.
  • Shows character conversion.
  • Useful for learning ASCII.

Drawbacks

  • Not intended for production use.
  • Prints control characters (0–31), which may not be visible.

ASCII vs Unicode

Feature ASCII Unicode
Character Count 128 Over 1.1 Million Code Points
English Support ✅ ✅
International Languages ❌ ✅
Emoji Support ❌ ✅
Used by Java Partially ✅

Example

ASCII

A

↓

65

Unicode

😊

↓

128522 (U+1F60A)

Important: Java char is a UTF-16 code unit. Characters outside the Basic Multilingual Plane (such as many emojis) require two char values (a surrogate pair). Use Unicode code point APIs when working with such characters.

UTF-8 vs UTF-16 Overview

Feature UTF-8 UTF-16
Encoding Size 1–4 Bytes 2 or 4 Bytes
ASCII Compatible ✅ No
Storage Efficiency Better for English Better for many Asian languages
Java String Storage Internally uses UTF-16 code units ✅

Edge Cases

Input Output
'A' 65
'a' 97
'0' 48
'@' 64
' ' 32
'\n' 10
'é' 233 (Unicode code point; also part of extended Latin, not standard ASCII)
'😊' Requires Unicode code point handling (cannot be represented by a single char)

Time & Space Complexity

Approach Time Extra Space
Type Casting O(1) O(1)
codePointAt() O(1) O(1)
Integer.valueOf() O(1) O(1)
Unicode APIs O(1) O(1)
ASCII Table Generation O(128) O(1)

Since 128 is a constant, printing the ASCII table is also considered O(1) with respect to input size.

Comparison of All Approaches

Approach Interview Friendly Performance Unicode Support Best Use Case
Type Casting ⭐⭐⭐⭐⭐ ⭐⭐⭐⭐⭐ ✅ Recommended interview solution
codePointAt() ⭐⭐⭐⭐ ⭐⭐⭐⭐⭐ ✅ Working with strings
Integer.valueOf() ⭐⭐⭐ ⭐⭐⭐⭐ ✅ Wrapper class demonstration
Unicode APIs ⭐⭐⭐⭐⭐ ⭐⭐⭐⭐⭐ ✅ International applications
ASCII Table Program ⭐⭐⭐⭐ ⭐⭐⭐⭐ N/A Learning and debugging

Common Interview Mistakes

Mistake 1

Thinking Java stores characters using ASCII.

Java stores characters using Unicode (UTF-16 code units).

ASCII values match Unicode only for characters in the range 0–127.

Mistake 2

Forgetting type casting.

Wrong

char ch = 'A';
System.out.println(ch);

Correct

System.out.println((int) ch);

Mistake 3

Confusing digits with numbers.

'5'

ASCII

53

Numeric value

5

They are different.

Mistake 4

Assuming every Unicode character fits in one char.

Many emojis require two UTF-16 code units (a surrogate pair).

Mistake 5

Using ASCII ranges for all languages.

ASCII range checks work only for English characters.

Interview Follow-up Questions

Q1. What is ASCII?

Q2. What is Unicode?

Q3. Why does Java use Unicode instead of ASCII?

Q4. What is the ASCII value of 'A'?

Q5. What is the difference between '5' and 5?

Q6. How do you convert an ASCII value back into a character?

Q7. What is UTF-8?

Q8. What is UTF-16?

Q9. Can Java store emojis in a single char?

Q10. How do you print the complete ASCII table?

Related Problems

  • Toggle Case
  • Character Frequency
  • Count Uppercase and Lowercase Characters
  • Count Digits and Special Characters
  • Check Unique Characters
  • Caesar Cipher
  • Reverse a String
  • Character Classification
  • Unicode Code Point Handling

Key Takeaways

  • ASCII assigns numeric values to the first 128 characters.
  • Java stores characters using Unicode (UTF-16 code units).
  • Type Casting is the simplest and most recommended interview solution.
  • codePointAt() and Unicode APIs are useful for multilingual applications.
  • Integer.valueOf() is mainly useful for demonstrating wrapper classes.
  • Understanding ASCII is essential for many String and Character interview questions.

Frequently Asked Interview Questions

Q1. Which solution is best for interviews?

Simple type casting is the preferred approach because it is concise, fast, and demonstrates an understanding of Java's char type.

Q2. Is Java based on ASCII?

No.

Java uses Unicode. ASCII is simply a subset of Unicode covering characters 0–127.

Q3. Why does (int) 'A' return 65?

The character 'A' has the Unicode code point 65, which is identical to its ASCII value.

Q4. What is the difference between 'A' and 65?

  • 'A' is a character.
  • 65 is an integer.
  • Casting converts the character to its numeric code point.

Q5. How do you convert an ASCII value into a character?

int value = 65;

char ch = (char) value;

System.out.println(ch);

Output

A

Interview Tip

If an interviewer asks:

"How do you find the ASCII value of a character in Java?"

Start with the type casting approach because it is the simplest and most commonly expected answer.

Then explain that Java actually uses Unicode, so for ASCII characters the Unicode code point and ASCII value are the same.

You can further impress the interviewer by discussing:

  1. Type Casting (recommended)
  2. codePointAt() for strings
  3. Unicode APIs for multilingual applications
  4. Printing the ASCII table programmatically
  5. The differences between ASCII, Unicode, UTF-8, and UTF-16

This demonstrates not only Java programming skills but also a solid understanding of character encoding, which is valuable for text processing and internationalization.