Java OOP Lab Manual

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• Identifier

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• Literal

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• Comment

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• Separator

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• Keyword

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• Whitespace

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Worked Examples

Example 1: Valid and invalid identifiers

• studentName is valid because it starts with a letter.

• marks2 is valid because digits may follow the first character.

• 2marks is invalid because an identifier cannot begin with a digit.

• class is invalid because it is a keyword.

• total_marks is valid; underscore is allowed.

Now you try: Classify value, 7value, static, and value$.

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Example 2: Reading literals and separators

int count = 10; char grade = 'A'; String subject = "Java"; System.out.println(subject + ": " + grade); • 10 is an integer literal.

• 'A' is a character literal; character values use single quotes.

• "Java" is a string literal; strings use double quotes.

•; ends each statement.

• () contains method arguments, and. accesses a member.

Now you try: Identify the literals and separators in double rate = 2.5;.

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Example 3: Comments and keywords

public class Demo { // Program entry point public static void main(String[] args) { int number = 5; /* integer literal */ System.out.println(number); } } • public, class, static, void, and int are keywords.

• Demo, main, String, args, and number are identifiers.

• The two comments are ignored during compilation.

• Braces define blocks; brackets define an array type.

Now you try: List the keywords and identifiers in private int total = 20;.

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Practice Questions

• (Easy) Define whitespace and give two examples.

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• (Easy) State whether firstName, 9items, and while are valid identifiers.

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• (Medium) Identify the literal types in boolean ready = true; char symbol = '#';.

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• (Medium) Explain the difference between // and /... / comments.

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• (Hard) Identify the keywords, identifiers, literals, and separators in public static int sum = 25;.

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Answer Key

• Whitespace includes spaces, tabs, and line breaks; it separates tokens.

• firstName valid; 9items invalid; while invalid because it is a keyword.

• true is a boolean literal; '#' is a character literal.

• // ends at the line break; /... / may span multiple lines.

• Keywords: public, static, int; identifiers: sum; literal: 25; separators: =,;.

Exam Tips & Common Mistakes

• Do not confuse character literals ( 'A' ) with string literals ( "A" ).

• Do not use keywords such as class, int, or return as identifiers.

• Check the first character of every identifier; digits may not appear first.

• Remember that Java

ignores comments, but comments cannot occur inside a token such as an identifier or keyword.

• Use indentation and line breaks to improve readability; they do not normally change program meaning.

• In an exam answer, classify each item precisely: token, identifier, literal, comment, separator, or keyword.

• Check spelling and capitalization because Java keywords and identifiers are case-sensitive.

• Remember that Java keywords are lowercase and cannot be used as names.

Examiner-focused tips:

• When asked to identify lexical elements, quote the exact source text and label each item.

• For code-tracing questions, first remove comments and whitespace mentally, then locate separators and keywords.

• In a definition question, include both the rule and a short Java example.

Quick Reference

Element

Rule

Example

Whitespace

Separates tokens; usually ignored

int n;

Identifier

Name; cannot start with a digit or be a keyword

studentCount

Integer literal

Whole-number value

42

Floating-point literal

Decimal value; f may mark float

3.14, 2.5f

Character literal

One character in single quotes

'A'

String literal

Text in double quotes

"Java"

Boolean literal

true or false

boolean ok = true;

Comment

Documentation ignored by compiler

// note

Separator

Marks structure or boundaries

;, {}, (), [],,,.

Keyword

Reserved Java word

class, if, return

Rules to remember:

• Identifiers: letters, digits, _, and $; the first character cannot be a digit.

• Java is case-sensitive: Count and count are different.

• Statements usually end with;.

• Blocks use { and }.

• Array declarations use [].

• Method calls use (); member access uses..

• Comments: // for one line, /... / for a block, and /*... / for documentation.

Mnemonic: WILCSK - W hitespace, I dentifiers, L iterals, C omments, S eparators, K eywords.

• Whitespace separates source-code tokens.

• Identifiers name program elements; keywords are reserved.

• Literals are fixed values written directly in code.

• Comments are ignored by the compiler.

• Separators show structure and boundaries.

Confidence Check

• I can explain why whitespace is used in Java source code. [ ] 1 [ ] 2 [ ] 3 [ ] 4 [ ] 5

• I can test whether an identifier

End of chapter one. 4 more chapters in the full book.