Identifiers and Literals ICSE Class 9: Tokens, Data Types and Type Conversion

What Identifiers and Literals is about

Weightage: CISCE publishes no chapter weightage and no question-paper layout for ICSE Class 9 Computer Applications. Class IX is examined by your school: one 100-mark theory paper of 2 hours, plus 100 marks of internal assessment (at least 15 programming assignments and a written project on ethical computing). This is topic 3 of the 2028 syllabus.Source: CISCE ICSE 2028 Computer Applications syllabus, Class IX

Key concepts

Character set, ASCII and Unicode

Character set: the characters Java accepts in a program:

• Letters: A-Z and a-z.
• Digits: 0-9.
• Special characters: + - * / % = < > ! & | ^ ~ ? : ; , . ' " ( ) { } [ ] _ @ # and others (including the dollar sign).
• White space: blank space, tab, new line.

ASCII (American Standard Code for Information Interchange): a code that gives each character a number from 0 to 127.

• A-Z: 65 to 90 (A = 65, Z = 90).
• a-z: 97 to 122 (a = 97, z = 122).
• 0-9: 48 to 57 (the digit '0' = 48, '9' = 57).
• Space: 32.

A lowercase letter's code is 32 more than its uppercase letter's code ('a' − 'A' = 32).

Unicode: a universal coding system that gives a unique number to every character of virtually every writing system in the world (Latin, Devanagari, Bengali, Tamil, Chinese, Arabic and more), as well as symbols. Java stores characters (char) in Unicode, using 16 bits (2 bytes). The first 128 Unicode characters are the same as ASCII.
Importance of Unicode in Java: globalisation and localisation (one program can show text in Hindi, Tamil or Japanese); reliable data exchange between computers and countries; consistent character handling (sorting, comparing) in any language.

Worked example

(2 marks) Give the output: System.out.println((int) 'A' + " " + (int) 'a' + " " + (int) '0' + " " + (int) ' ');

Try it first, then show the solutionSolution

1. Codes: 'A' = 65, 'a' = 97 - 1 mark.
2. '0' = 48, space = 32; joined with spaces - 1 mark.

Answer: 65 97 48 32

Escape sequences

An escape sequence is a backslash (\) followed by a character, used inside character or string literals to represent characters that cannot be typed directly or have a special meaning. It counts as a single character.

The five in the syllabus:

• \n: new line (moves the cursor to the next line).
• \t: horizontal tab (moves to the next tab stop).
• \\: prints a backslash.
• \": prints a double quote inside a string.
• \': prints a single quote (needed inside a char literal: '\'').

As run in this study guide:
System.out.println("Name\tClass\nRiya\tIX");
System.out.println("He said, \"Java\'s fun\"");
System.out.println("C:\\BlueJ\\Projects");
Output:
Name Class
Riya IX
He said, "Java's fun"
C:\BlueJ\Projects
(The gaps are tab characters.)

Worked example

(2 marks) Write a single println() statement to print:
Teacher said "Well done"
and then the next line.

Try it first, then show the solutionSolution

1. Use \" for each double quote inside the string - 1 mark.
2. Statement: System.out.println("Teacher said \"Well done\""); - 1 mark.

Answer: System.out.println("Teacher said \"Well done\"");

Tokens: keywords, identifiers, literals, punctuators, operators

A token is the smallest individual unit of a program that the compiler recognises.

1. Keywords (reserved words): words with a fixed meaning in Java that cannot be used as names. Examples: class, int, double, char, boolean, if, else, for, while, do, switch, case, break, new, void, public, static, import, return.

2. Identifiers: names given by the programmer to variables, classes, methods and objects. Rules:

• may contain letters, digits, underscore (_) and the dollar sign;
• must not begin with a digit;
• must not contain spaces or other special characters;
• must not be a keyword (or the literals true, false, null);
• are case sensitive (marks and Marks are different);
• can be of any length.

Valid: totalMarks, _rate, area2, rollNo. Invalid: 2area (starts with a digit), total marks (space), class (keyword), net-pay (hyphen).
Conventions: class names start with a capital letter (Student); variables and methods start with a small letter (rollNo, findArea).

3. Literals (constants): fixed values written in the program:

• integer literals: 25, -7, 0, 100L (long);
• floating-point (real) literals: 3.14, -0.5, 2.5f (float), 1.2e3;
• character literals: one character in single quotes: 'A', '7', '\n';
• string literals: characters in double quotes: "ICSE", "" (empty);
• boolean literals: true, false;
• null literal: null.

4. Punctuators (separators): ; , . ( ) { } [ ]

5. Operators: symbols that perform operations: + - * / % = == < > && || ! ++ --

Worked example

(2 marks) State whether each identifier is valid; give a reason if invalid: (i) _total (ii) 3rdTerm (iii) net pay (iv) price_2

Try it first, then show the solutionSolution

1. (i) valid; (ii) invalid: begins with a digit - 1 mark.
2. (iii) invalid: contains a space; (iv) valid - 1 mark.

Answer: (i) Valid. (ii) Invalid: cannot begin with a digit. (iii) Invalid: contains a space. (iv) Valid (letters, underscore and digit, not first).

Variables, constants and data types

Variable: a named memory location that stores a value which can change while the program runs. Declared with a type: int marks = 85;
Constant: a named value that cannot be changed once assigned, declared with the keyword final: final double RATE = 8.5; Trying to change RATE gives a compile-time error. Literals are also constants.

Primitive data types (built into Java; size fixed):

• byte: 8 bits (1 byte); −128 to 127.
• short: 16 bits (2 bytes); −32,768 to 32,767.
• int: 32 bits (4 bytes); about −2.1 billion to 2.1 billion (2,147,483,647 maximum).
• long: 64 bits (8 bytes); very large whole numbers.
• float: 32 bits (4 bytes); decimal numbers, about 6-7 significant digits; literal needs f (2.5f).
• double: 64 bits (8 bytes); decimal numbers, about 15 significant digits; the default for decimal literals.
• char: 16 bits (2 bytes); one Unicode character.
• boolean: true or false; Java does not fix its size (textbooks often describe it as 1 bit).

Non-primitive (reference) data types: built from primitives, store a reference to an object: classes (including String and Scanner), arrays and interfaces. Example: String name = "Riya";

Default values of data members: 0 for numeric types, 0.0 for float and double, '\u0000' for char, false for boolean, null for references.

Worked example

(2 marks) State the size in bits and bytes of: (i) char (ii) long (iii) float (iv) short.

Try it first, then show the solutionSolution

1. char 16 bits = 2 bytes; long 64 bits = 8 bytes - 1 mark.
2. float 32 bits = 4 bytes; short 16 bits = 2 bytes - 1 mark.

Answer: (i) char: 16 bits (2 bytes). (ii) long: 64 bits (8 bytes). (iii) float: 32 bits (4 bytes). (iv) short: 16 bits (2 bytes).

Implicit type conversion (type promotion)

Implicit (automatic, widening) conversion is done by Java itself when a value of a smaller type is used where a larger type is expected. The value is not cut down (the one exception: a very large int or long converted to float may lose its last digits of precision, e.g. 123456789 becomes 1.23456792E8).
Order: byte → short → int → long → float → double; and char → int.

Examples (as run in this study guide):

• int i = 7; double d = i; prints 7.0
• 'A' + 1 → char promoted to int: 66
• char ch = 'M'; int code = ch + 0; prints 77
• 'A' + 'B' → both promoted to int: 65 + 66 = 131 (not "AB")
• "" + 'A' + 'B' → string joining: AB

In an expression with mixed types, every operand is promoted to the largest type present before the operation: 5 / 2.0 gives 2.5 because 5 is promoted to double.
Integer division: when both operands are integers, the result is an integer and the fraction is dropped: 5 / 2 gives 2.

Worked example

(2 marks) Give the output: System.out.println('A' + 'B'); System.out.println("" + 'A' + 'B');

Try it first, then show the solutionSolution

1. 'A' + 'B': both chars promoted to int: 65 + 66 = 131 - 1 mark.
2. "" + 'A' makes a String, then 'B' is joined: AB - 1 mark.

Answer: 131
AB

Explicit type conversion (type casting)

Explicit conversion (type casting, narrowing) is requested by the programmer by writing the target type in brackets before the value: (type) value. It is needed to convert a larger type into a smaller one, and data may be lost.

Examples (as run in this study guide):

• (int) 7.9 gives 7 (the fraction is cut off, not rounded).
• (char) 98 gives 'b'.
• (char) ('A' + 2) gives 'C'.
• (double) 5 / 2 gives 2.5 (5 becomes 5.0 before dividing).
• (double) (5 / 2) gives 2.0 (5 / 2 is 2 first, then converted).
• (byte) 130 gives −126, because 130 does not fit in a byte (range −128 to 127) and wraps around.

Overflow without a cast: if int over = 2147483647; over = over + 1; then over becomes −2147483648, because int cannot hold a larger value. Using long avoids this: a long holding 2147483647 plus 1 gives 2147483648.

Implicit vs explicit:
1. Implicit is done automatically; explicit is written by the programmer.
2. Implicit converts smaller to larger (widening); explicit usually larger to smaller (narrowing).
3. Implicit loses no data; explicit may lose data.

Worked example

(2 marks) Give the output: System.out.println(5 / 2 + " " + 5 / 2.0 + " " + (double) 5 / 2 + " " + (double) (5 / 2));

Try it first, then show the solutionSolution

1. 5 / 2 = 2 (integer division); 5 / 2.0 = 2.5 - 1 mark.
2. (double) 5 / 2 = 2.5; (double) (5 / 2) = 2.0 - 1 mark.

Answer: 2 2.5 2.5 2.0

Identifiers and Literals in real life

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

Topics in this chapter

• Character Set, ASCII, Unicode, Escape Sequences and Tokens in Java
• Variables, Constants, Primitive Data Types and Type Conversion

Identifiers and Literals: syntax and key facts

ASCII ranges

A-Z: 65-90; a-z: 97-122; 0-9: 48-57; space: 32

lowercase = uppercase + 32.

Escape sequences

\n new line; \t tab; \\ backslash; \" double quote; \' single quote

Each counts as one character.

Sizes

byte 8 bits (1 B); short 16 (2 B); int 32 (4 B); long 64 (8 B); float 32 (4 B); double 64 (8 B); char 16 (2 B)

boolean: true/false.

Widening order

1. 1.byte
2. 2.short
3. 3.int
4. 4.long
5. 5.float
6. 6.double; char
7. 7.int

Implicit; no data lost.

Cast

(type) value, e.g. (int) 7.9 = 7; (char) 98 = 'b'

Explicit; may lose data.

How the school exam asks Identifiers and Literals

The question patterns to expect, and the method that works for each.

Tricks to remember Identifiers and Literals

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

• 65, 97, 48, 32

  Capital A sits at 65, small a is 32 places later at 97, the digit 0 is at 48, and the space is at 32 (the same gap as between cases).

  Use it when: ASCII anchors.

• KILPO

  Tokens: Keywords, Identifiers, Literals, Punctuators, Operators.

  Use it when: Five token types.

• 1-2-4-8 and 2-4-8

  byte 1, short 2, int 4, long 8 bytes; char 2, float 4, double 8 bytes.

  Use it when: Sizes.

Identifiers and Literals: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section B style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 7-mark question split into 2 + 2 + 3 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Identifiers and Literals

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

• ✗Mistake: Treating 'A' + 'B' as "AB"

  Thinking + always joins text.

  Wrong working

  System.out.println('A' + 'B'); prints AB

  Right working

  Two chars are added as numbers: 131. Only if a String is involved does + join.

  ✓Do this: Check from left to right whether a String has appeared yet.

  Usually costs: 1 mark.

• ✗Mistake: Rounding when casting

  Everyday rounding habit.

  Wrong working

  (int) 7.9 = 8

  Right working

  (int) 7.9 = 7 (fraction dropped).

  ✓Do this: Casting to int truncates towards zero.

  Usually costs: 1 mark.

• ✗Mistake: Wrong ASCII values

  Ranges not memorised.

  ✓Do this: A 65, a 97, 0 48, space 32; count on from these.

  Usually costs: 1 mark per value.

• ✗Mistake: Integer division in averages

  Forgetting both operands are int.

  Wrong working

  double avg = (18 + 17) / 2; gives 17.0

  Right working

  double avg = (18 + 17) / 2.0; gives 17.5

  ✓Do this: Make one operand double before dividing.

  Usually costs: 1 to 2 marks.

Practice questions on Identifiers and Literals

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 · MCQExam level

   The ASCII value of 'z' is:
   (a) 90
   (b) 122
   (c) 97
   (d) 126

   Hint

   a = 97.

   Answer

   (b) 122

2. Q2 · 1 mark · MCQExam level

   Which of these is NOT a primitive data type?
   (a) char
   (b) boolean
   (c) String
   (d) long

   Hint

   It is a class.

   Answer

   (c) String

3. Q3 · 1 mark · MCQHarder exam level

   Which of these is a valid identifier?
   (a) final
   (b) roll-no
   (c) _roll2
   (d) 2roll

   Hint

   Keyword, hyphen, digit first.

   Answer

   (c) _roll2

4. Q4 · 2 marks · Very short answerHOTS / competency

   Give the output: System.out.println((byte) 130);

   Hint

   byte range −128 to 127.

   Answer

   -126 (130 is outside the byte range and wraps: 130 − 256 = −126).

5. Q5 · 2 marks · Very short answerExam level

   State two differences between primitive and non-primitive data types.

   Hint

   Built-in; value vs reference.

   Answer

   (1) Primitive types are built into Java (int, char); non-primitive types are created from them (classes, arrays). (2) A primitive variable stores the value itself with a fixed size; a non-primitive variable stores a reference to an object.

6. Q6 · 2 marks · Very short answerHarder exam level

   Why is Unicode essential in Java? Give two reasons.

   Hint

   Global use.

   Answer

   (1) It can represent characters of virtually every language, so programs can be localised for users worldwide. (2) It gives every character one standard code, so text is exchanged and handled consistently between computers.

7. Q7 · 2 marks · Very short answerHarder exam level

   Give the output: char ch = 'M'; int code = ch + 0; System.out.println(code); final double RATE = 8.5; System.out.println(RATE * 2);

   Hint

   M = 65 + 12.

   Answer

   77
   17.0

8. Q8 · 2 marks · Very short answerHarder exam level

   Write statements to (i) print the character whose ASCII code is 100, and (ii) print the ASCII code of '#' (do not work it out; let Java do it).

   Hint

   Cast both ways.

   Answer

   (i) System.out.println((char) 100); (prints d)
   (ii) System.out.println((int) '#');

9. Q9 · 15 marks · Long answerHarder exam level

   Write a program that stores a lowercase letter 'k', converts it to uppercase using its code, and prints both letters with their ASCII codes, separated by tabs.

   Hint

   Subtract 32 and cast.

   Answer

   class ToUpper
   {
   public static void main(String args[])
   {
   char low = 'k';
   char up = (char) (low - 32);
   System.out.println(low + "\t" + (int) low);
   System.out.println(up + "\t" + (int) up);
   }
   }
   Output (as run; gaps are tabs):
   k 107
   K 75

10. Q10 · 2 marks · Short answerHOTS / competency

    A student writes float price = 49.99; and gets a compile-time error. Explain why and give two ways to fix it.

    Hint

    Default type of decimal literals.

    Answer

    A decimal literal such as 49.99 is a double by default, and Java will not implicitly narrow double to float because data could be lost. Fix: float price = 49.99f; or float price = (float) 49.99; (or declare price as double).

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 value of '0'?Show answer

   48

2. 2.Escape sequence for a tab?Show answer

   \t

3. 3.Size of double in bytes?Show answer

   8 bytes (64 bits).

4. 4.Keyword used to declare a constant?Show answer

   final

5. 5.Another name for explicit conversion?Show answer

   Type casting.

6. 6.Can an identifier begin with an underscore?Show answer

   Yes (for example _total); it cannot begin with a digit.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐ASCII: A-Z 65-90, a-z 97-122, 0-9 48-57, space 32; Java char uses 16-bit Unicode.
• ☐Escapes: \n \t \\ \" \'.
• ☐Tokens: keywords, identifiers, literals, punctuators, operators.
• ☐Identifiers: letters, digits, underscore and dollar sign; no digit first, no space, no keyword; case sensitive.
• ☐byte 1, short 2, int 4, long 8, float 4, double 8, char 2 bytes; String is non-primitive.
• ☐Implicit: widening, automatic; explicit: (type) cast, may lose data; 5 / 2 = 2.

Identifiers and Literals: frequently asked questions