Skip to content

Java ASCII, Unicode, Escape Sequences, Tokens: ICSE 9

questionbuddy.in/icse/class-9/computer-applications/identifiers-and-literals/character-set-ascii-unicode-escape-sequences-and-tokens

Computer ApplicationsICSE Class 9 · Identifiers and Literals

Character Set, ASCII, Unicode, Escape Sequences and Tokens in Java (ICSE Class 9)

Updated 18 October 2026 · Fact-checked

Java programs are made of characters (letters, digits, special characters, white space) coded by ASCII (A-Z 65 to 90, a-z 97 to 122, 0-9 48 to 57, space 32) and, more widely, by Unicode. Escape sequences such as \n \t \\ \" \' represent special characters. A token is the smallest unit the compiler recognises: keywords, identifiers, literals, punctuators and operators; identifiers follow naming rules.

Notice that one short statement breaks into five tokens, and each token belongs to exactly one type.

Illustration drawn for QuestionBuddy.

Understand Character Set, ASCII, Unicode, Escape Sequences and Tokens in Java

Character set. Letters A-Z and a-z, digits 0-9, special characters (such as + - * / % = < > ! & | ( ) { } [ ] ; , . and the underscore) and white space (blank, tab, new line).

ASCII. A code that gives each character a number from 0 to 127. A-Z are 65 to 90, a-z are 97 to 122, the digits 0-9 are 48 to 57 and the space is 32. A small letter's code is 32 more than its capital's ('a' - 'A' is 32). When a char is used in arithmetic, its code is used: 'A' + 1 is 66.

Unicode. A universal coding system that gives a unique number to the characters of virtually every writing system and to symbols. Java stores a char in 16 bits using Unicode, and its first 128 characters are the same as ASCII. Importance: one program can show text in many languages, data can be exchanged reliably between computers, and characters are handled in a consistent way.

Escape sequences. A backslash followed by a character, counted as a single character: \n new line, \t tab, \\ backslash, \" double quote, \' single quote.
Example: System.out.println("He said \"Hi\""); prints He said "Hi".

Tokens. The smallest units a compiler recognises.
1. Keywords: reserved words with a fixed meaning (class, int, double, if, else, for, while, new, void, public, static, import, return, final) that cannot be used as names.
2. Identifiers: names chosen by the programmer for variables, classes, methods and objects.
3. Literals: fixed values written in the program: integer (25), floating-point (3.14), character ('A'), string ("ICSE"), boolean (true, false) and null.
4. Punctuators (separators): ; , . ( ) { } [ ]
5. Operators: + - * / % = == < > && || ! ++ --

Rules for identifiers. Letters, digits, underscore and the dollar sign are allowed; the first character must not be a digit; no spaces or other special characters; it must not be a keyword; it is case sensitive and can be of any length. Conventionally class names begin with a capital letter and variables and methods with a small letter.

Neighbouring topics: variables, constants, data types and type conversion are on the next page of this chapter.

Character Set, ASCII, Unicode, Escape Sequences and Tokens in Java: key facts

ASCII ranges
A-Z65 to 90
a-z97 to 122
0-948 to 57
space32
Small letter = capital + 32.
Escape sequences
new linebackslash n
tabbackslash t
backslashtwo backslashes
double quotebackslash then quote
Each counts as one character.
Five tokens
  • Keywords
  • identifiers
  • literals
  • punctuators
  • operators
Smallest units of a program.
Identifier rules
  • Letters, digits, underscore, dollar
  • not starting with a digit
  • no spaces
  • not a keyword
  • case sensitive
Class name starts with a capital.

Character Set, ASCII, Unicode, Escape Sequences and Tokens in Java in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Unicode on a school certificate

Suppose a school prints each student's name on a certificate in English and also in the student's home language, such as Bengali or Marathi.

Why does the certificate program need Unicode and not only ASCII?

Try it first, then show the solutionSolution
  1. ASCII has only 128 codes, enough for English letters but not for Bengali or Marathi letters.
  2. Unicode gives a code to the characters of these scripts.
  3. So the same program can print every name correctly.

Answer: Unicode lets one program store and show text in many scripts with consistent codes.

Memory hook: One code system for all scripts.

Tricks to remember Character Set, ASCII, Unicode, Escape Sequences and Tokens in Java

Short memory aids. Say each one aloud once, then use it on a question the same day.

  • 65, 97, 48, 32

    A is 65, a is 97, 0 is 48, space is 32.

    Use it when: ASCII values.

  • Backslash starts the magic

    Every escape sequence starts with a backslash and counts as one character.

    Use it when: Escape sequences.

  • KILPO

    Keywords, Identifiers, Literals, Punctuators, Operators.

    Use it when: Five kinds of tokens.

Character Set, ASCII, Unicode, Escape Sequences and Tokens in Java: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: ASCII value · 1 mark · MCQBoard level

The ASCII code of the capital letter A is:
(a) 97 (b) 65 (c) 48 (d) 32

Try it first, then show the solutionSolution
  1. Capital letters start at 65; 97 is a small a, 48 is the digit 0, 32 is space.

Answer: (b) 65

Example 2: Characters and codes · 3 marks · Short answerHarder board level

Find the output:

System.out.println((char) ('a' + 3) + " " + (int) 'Z' + " " + (char) 101);
Try it first, then show the solutionSolution
  1. (char) ('a' + 3): 97 + 3 = 100, which is the character d. (1 mark)
  2. (int) 'Z' is 90. (1 mark)
  3. (char) 101 is e. The parts are joined with spaces: d 90 e. (1 mark)

Answer: d 90 e

Example 3: Escape sequences in one statement · 3 marks · Short answerHarder board level

Show the output of:

System.out.println("Name:\tRia\nClass:\t\"IX\"\nPath: C:\\data");
Try it first, then show the solutionSolution
  1. \n starts a new line and \t gives a tab gap, so there are three lines. (1 mark)
  2. \" prints a double quote inside the text. (1 mark)
  3. \\ prints one backslash. Output: Name: (tab) Ria; Class: (tab) "IX"; Path: C:\data. (1 mark)

Answer: Name:<tab>Ria
Class:<tab>"IX"
Path: C:\data

Example 4: Case study: classify the tokens · 4 marks · Case-basedHOTS / competency

Consider the statement final int MAX = 100;
(i) List all the tokens and name the kind of each. (3)
(ii) What does final do to MAX? (1)

Try it first, then show the solutionSolution
  1. (i) final: keyword; int: keyword; MAX: identifier; =: operator; 100: integer literal; ;: punctuator.
  2. (ii) final makes MAX a constant, so its value cannot be changed after assignment.

Answer: (i) final (keyword), int (keyword), MAX (identifier), = (operator), 100 (literal), ; (punctuator) (ii) MAX becomes a constant

Example 5: Character arithmetic · 3 marks · Short answerHarder board level

Find the output:

char c = 'M';
c = (char) (c + 2);
int d = c - 'A';
System.out.println(c + " " + d);
Try it first, then show the solutionSolution
  1. 'M' is 77, so c + 2 = 79, which is the character O. (1 mark)
  2. d = 79 - 65 = 14. (1 mark)
  3. Output: O 14. (1 mark)

Answer: O 14

Where students lose marks in Character Set, ASCII, Unicode, Escape Sequences and Tokens in Java

The slips examiners see most often, and what to write instead.

  • Mistake: Writing 0 for the code of the digit 0

    The digit and the number are mixed.

    Wrong working

    ASCII of '0' is 0

    Right working

    ASCII of '0' is 48

    Do this: Digits start at 48.

    Usually costs: 1 mark

  • Mistake: Calling a hyphen valid in a name

    Hyphens look like underscores.

    Wrong working

    net-pay is valid

    Right working

    net-pay is invalid; net_pay is valid

    Do this: Only letters, digits, underscore and dollar.

    Usually costs: 1 mark

  • Mistake: Single backslash in a path

    Escape sequences are ignored.

    Wrong working

    "C:\data" written with a single backslash

    Right working

    Use two backslashes

    Do this: A backslash must be escaped.

    Usually costs: 1 mark

Exam tips

  • Memorise 65, 97, 48 and 32.
  • Count each escape sequence as one character.
  • List all five kinds of tokens when asked.
  • When a char appears in arithmetic, convert it to its code first.

Practice questions on Character Set, ASCII, Unicode, Escape Sequences and Tokens in Java

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

  1. Q1 · 1 mark · MCQBoard level

    Which of these is a valid identifier?
    (a) 2nd_rank (b) rank_2 (c) rank 2 (d) rank-2

    Hint

    No digit first, no space, no hyphen.

    Answer

    (b) rank_2

  2. Q2 · 2 marks · Very short answerBoard level

    Give the ASCII range of (i) small letters (ii) digits.

    Hint

    Remember the starting values.

    Answer

    (i) 97 to 122 (ii) 48 to 57

  3. Q3 · 2 marks · Short answerHarder board level

    Find the output:

    System.out.println('a' + 1 + " " + (char) ('a' + 1));
    Hint

    The char becomes an int in arithmetic.

    Answer

    98 b ('a' + 1 = 98 as numbers; the second part is the character with code 98)

  4. Q4 · 3 marks · Short answerHarder board level

    Write one println() statement that prints exactly: He said "Hi" and the path D:\files

    Hint

    Escape the quotes and the backslash.

    Answer

    System.out.println("He said \"Hi\" and the path D:\\files");

  5. Q5 · 3 marks · Short answerHOTS / competency

    Explain with an example why Unicode is needed even though ASCII already has codes for letters.

    Hint

    What does ASCII not cover?

    Answer

    ASCII has only 128 codes, enough for English letters, digits and common symbols but not for scripts such as Devanagari or Tamil. Unicode gives a unique number to the characters of virtually every script, so a program can store a name written in Hindi or Tamil and show it correctly.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

  1. 1.ASCII code of a?Show answer

    97

  2. 2.ASCII code of the space?Show answer

    32

  3. 3.Which escape sequence is the tab?Show answer

    Backslash t.

  4. 4.How many bits does a char take?Show answer

    16 bits.

  5. 5.Is true a keyword or a literal?Show answer

    A boolean literal.

  6. 6.Can an identifier start with a digit?Show answer

    No.

Character Set, ASCII, Unicode, Escape Sequences and Tokens in Java: frequently asked questions

Is the dollar sign allowed in an identifier?

Yes, but it is rarely used.

Is Java case sensitive?

Yes. Marks and marks are different identifiers.

Are Unicode and ASCII the same?

The first 128 Unicode characters are the same as ASCII; Unicode has many more.