🧭 Module 2 – Java Language

Author: Srinivas DandeSource: Java Learning Center – Study Guide

2.1 Character Sets

Java recognizes three types of character elements:

• Alphabets – A–Z, a–z
• Digits – 0–9
• Special Characters – + - * & % $ ! < > { } = ~ ^ etc.

TIP

Java uses Unicode to represent all characters, allowing it to support multiple languages and symbols.

2.2 Keywords

Keywords are predefined reserved words in Java with special meaning that cannot be redefined or used as identifiers.

INFO

All Java keywords are lowercase and have fixed meaning.

Key Points

• There were 49 keywords up to Java 2.
• enum was added in Java 5 → total 50 keywords.
• const and goto are reserved but not implemented.
• true, false, and null are literals, not keywords.

📜 List of Keywords

Category	Keywords
Data Types (8)	boolean, byte, char, short, int, long, float, double
Class & Object (9)	class, interface, enum, extends, implements, this, super, new, instanceof
Access Modifiers (3)	private, protected, public
Other Modifiers (9)	final, native, abstract, synchronized, transient, volatile, static, const*, strictfp
Package (2)	package, import
Control Statements (12)	if, else, switch, case, default, do, while, break, for, continue, return, goto*
Exception Handling (6)	try, catch, finally, throw, throws, assert
Other (1)	void

2.3 Identifiers

Identifiers are names used to identify programming elements (classes, methods, variables, etc.). They are also known as user-defined names.

✅ Rules for Identifiers

• May contain letters, digits, $, and _
• Must start with a letter, $, or _
• Cannot use Java keywords or reserved words
• Case-sensitive

✅ Valid	❌ Invalid
Hello	1stClass
Int	true
getClassName	student number
studentEmail	student-email
TOTAL_FEE	int

2.4 Data Types

Data types specify:

• Type of data to store
• Memory allocation required

Two major categories:

1. Primitive Data Types
2. User Defined Data Types

2.4.1 Primitive Data Types

There are 8 primitive data types in Java, each with a keyword.

Category	Data Types
Boolean Type	boolean
Integral Types	byte, short, int, long, char
Floating Point Types	float, double

2.4.2 User Defined Data Types

Four types of User-Defined Data Types:

1. class
2. interface
3. enum (added in Java 5)
4. @annotation (added in Java 5)

2.4.3 Primitive Type Summary

Type	Size (Bytes)	Bits	Default Value	Min	Max
boolean	N/A	N/A	false	true/false	—
byte	1	8	0	-128	127
char	2	16	\u0000	0	65535
short	2	16	0	-32768	32767
int	4	32	0	-2³¹	2³¹-1
long	8	64	0	-2⁶³	2⁶³-1
float	4	32	0.0	1.4E-45	3.4E38
double	8	64	0.0	4.9E-324	1.79E308
Reference	8	64	null	—	—

2.5 Variables

Variables are containers that hold user data.

int a;
String str;
int a = 99;
String str = "SRI";

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Memory for variables is allocated at runtime, not compile-time.

2.5.1 Primitive Variables

Declared with primitive data types:

int a = 99;
double d = 9.9;
boolean b = true;

2.5.2 Reference Variables

Declared using user-defined data types (like classes, interfaces, arrays):

String str = "JLC";
Hello h = new Hello();

🧪 Lab Example

class Hello {
  boolean b1;
  byte b2;
  short s;
  int a;
  long b;
  float f;
  double d;
  String str;
  Hello h;

  void show() {
    System.out.println(b1);
    System.out.println(b2);
    System.out.println(s);
    System.out.println(a);
    System.out.println(b);
    System.out.println(f);
    System.out.println(d);
    System.out.println(str);
    System.out.println(h);
  }
}

class Lab1 {
  public static void main(String[] as) {
    Hello h = new Hello();
    h.show();
  }
}

⚖️ Primitive vs Reference Variables

Primitive Variables	Reference Variables
Declared with primitive types	Declared with user-defined/reference types
Memory depends on type	Always 8 bytes (reference to object)
Hold literal value	Hold object reference or null
Default depends on data type	Default is always null

2.5.3 Variables by Scope

1. Instance Variables: Declared in class, without static.

2. Static Variables: Declared with static.

3. Local Variables: Declared inside a method or block.

class Hello {
  int a;           // Instance
  static int b;    // Static
  void show() {
    int c;         // Local
  }
}

2.6 Constants

A constant is a special variable whose value cannot be modified after initialization.

final int A = 99;
final String STR = "JLC";
final double D1 = 999.99;

INFO

Constants are declared using the final keyword.

Syntax

[modifier] final <dataType> <varName> = <value>;

Blank Final Variable

A blank final is a variable declared as final but initialized later.

final int A;
A = 98;

TIP

Once initialized, the value of a final variable cannot be changed.

Examples

✅ Valid Final Declaration

final int A = 99;
System.out.println(A);

❌ Invalid Reassignment

final int A = 99;
A = 88; // Compilation Error

✅ Blank Final Example

final int A;
A = 99;
System.out.println(A);

🧠 Notes Summary

1. const keyword exists but is not implemented in Java. Use final instead.
2. Final variables are replaced by literal values in compiled class files.
3. Value of a final variable cannot be reassigned.
4. Final variables must be initialized before use.

2.7 Literals

Literals are the actual fixed values assigned to variables or constants in a program.

Classification

2.7.1 Boolean Literals

A boolean literal can have only two values:

boolean b1 = true;
boolean b2 = false;

WARNING

Boolean variables cannot hold numeric values like 1 or 0.

Invalid:

boolean b = 1; // ❌ Compilation Error

2.7.2 Character Literals

Character literals represent a single character enclosed in single quotes 'A'.

A char can hold:

1. A single character
2. An escape sequence
3. An ASCII value
4. A Unicode character
5. An Octal value

Example

char ch1 = 'A';
char ch2 = '\u0041'; // Unicode
char ch3 = '\101';   // Octal
char ch4 = 65;       // ASCII

2.7.2.1 Escape Sequences

Escape sequences represent special characters that cannot be typed directly.

Escape	Description
\t	Tab space
\b	Backspace
\n	New line
\r	Carriage return
\f	Form feed
\'	Single quote
\"	Double quote
\\	Backslash

char singleQuote = '\'';
char doubleQuote = '\"';
char backslash = '\\';

2.7.2.2 ASCII Character Set

ASCII (American Standard Code for Information Interchange) represents characters as integers from 0–255.

char ch1 = 65; // 'A'
char ch2 = 97; // 'a'
System.out.println(ch1 + " " + ch2);

Character	ASCII	Octal	Unicode
A	65	101	\u0041
a	97	141	\u0061
0	48	060	\u0030
9	57	071	\u0039

2.7.2.3 Unicode Characters

Unicode is used for internationalization, representing characters from all languages.

• Range: \u0000 → \uFFFF
• Always written as: \u + 4 hexadecimal digits

char ch = '\u0061'; // 'a'
System.out.println(ch);

2.7.2.4 Octal Values

Characters can also be represented using octal notation.

• Syntax: \DDD (D = octal digit)
• Range: \0 → \377 (0–255 decimal)

char ch = '\101'; // 'A'

TIP

When you print a char assigned with ASCII, Unicode, or Octal, it shows the corresponding character.

2.7.3 String Literals

A string literal is a sequence of zero or more characters enclosed in double quotes.

String str1 = "";
String str2 = "JLCINDIA";
String str3 = "JLC99@india";

Type	Example	Length	Description
Null String	String s = null;	N/A	No object reference
Empty String	String s = "";	0	Valid object with no characters

WARNING

Accessing members (s.length()) on a null string causes NullPointerException.

Example

String str1 = null;
System.out.println(str1.length()); // ❌ Exception

String str2 = "";
System.out.println(str2.length()); // ✅ 0

2.7.4 Integer Literals

Integer literals represent whole numbers.

Types:

1. Decimal (Base 10)
2. Octal (Base 8)
3. Hexadecimal (Base 16)
4. Binary (Base 2 – from Java 7)

Decimal Literals

• Use digits 0–9
• Must not start with 0

int num = 12345;
long big = 2147483648L; // ‘L’ suffix for long

Octal Literals

• Must start with 0
• Digits allowed: 0–7

int num = 0101; // octal for 65

Hexadecimal Literals

• Must start with 0x or 0X
• Digits allowed: 0–9, A–F, a–f

int hex = 0xA;
int val = 0xFACE;

Binary Literals (Java 7+)

• Must start with 0b or 0B
• Digits allowed: 0 or 1

int a = 0b1010;
System.out.println(a); // 10

INFO

If invalid digits are used (like 0b102), you’ll get a compilation error.

2.7.5 Floating Point Literals

Floating literals represent decimal numbers. Default type: double.

Standard Notation

double d = 123.456;
float f = 12.34F; // ‘F’ or ‘f’ required for float

Scientific Notation

double d1 = 1.23e2;  // 1.23 × 10² = 123.0
float f1 = 9.8e-3F;  // 9.8 × 10⁻³ = 0.0098

Hexadecimal Floating (Java 5+)

double d1 = 0xAp0;  // 10.0
double d2 = 0xAp1;  // 20.0
double d3 = 0xAp2;  // 40.0

2.7.6 Null Literal

• null is a literal representing no object reference.
• Default value for all reference variables.

String name = null;
System.out.println(name); // prints null

2.7.7 Underscore in Numeric Literals (Java 7+)

Underscores improve readability in numbers.

int a = 2_45_12_452;
double d = 1_234.56;
long card = 9_876_543_210L;

WARNING

Underscores cannot appear:

• At the beginning or end
• Next to a decimal point
• Immediately after 0x, 0b, or 0

💡 Literals Summary

Category	Notes
Boolean	Only true or false, lowercase only
Character	Single quote, can use escape, ASCII, Unicode, or Octal
String	Double quotes, supports escape sequences
Integer	Decimal, Octal, Hexadecimal, Binary
Floating	Standard, Scientific, Hexadecimal
Null	Represents no reference
Underscore	Improves readability (Java 7+)

📘 Assignment #1 – Variables and Constants

1. How many keywords are available prior to Java 5?
2. What keyword was added newly in Java 5?
3. Which keywords cannot be used in a Java program?
4. What is an identifier and what rules apply?
5. What is the default value of char?
6. What is a variable and how many types exist?
7. What is a constant?
8. Can you use const to declare constants?
9. When is memory allocated for a variable?
10. What’s the difference between instance, static, and local variables?

📗 Assignment #2 – Literals

1. What is a literal and how many types are available?
2. What happens if 1 is assigned to a boolean?
3. What is the escape sequence for a double quote?
4. What are the ranges of ASCII and Unicode?
5. What’s the difference between a null string and an empty string?
6. What happens when you use Unicode inside a string literal?
7. Can underscore appear after 0x in hexadecimal?
8. Can underscore be used after a decimal point?

2.8 Operators

Operators are symbols used to perform operations on operands. Each operator has a defined operation type and number of operands.

🧩 Operator Types by Operand Count

Type	Example	Description
Unary	++a, --b, !a	Operates on a single operand
Binary	a + b, x > y	Operates on two operands
Ternary	a ? b : c	Operates on three operands

🔢 Operator Categories by Function

2.8.1 Arithmetic Operators

Arithmetic operators perform mathematical operations.

Operator	Description
+	Addition
-	Subtraction
*	Multiplication
/	Division
%	Modulus (Remainder)

INFO

Operands can be numeric or char type. Result is always int or wider than int.

2.8.1.1 Unary Arithmetic Operators

Operator	Description
+	Returns the same value
-	Returns the same value with opposite sign

int a = 19;
int b = +a;  // 19
int c = -a;  // -19

2.8.1.2 Binary Arithmetic Operators

int a = 10;
int b = 3;
System.out.println(a + b); // 13
System.out.println(a - b); // 7
System.out.println(a * b); // 30
System.out.println(a / b); // 3
System.out.println(a % b); // 1

Operator Result Rules

Operand 1	Operand 2	Result Type
byte	byte	int
char	char	int
short	byte	int
int	long	long
byte	double	double
float	int	float
float	long	float
char	double	double

🔍 Examples

Example 1

byte a = 10, b = 20;
byte c = (byte)(a + b); // must cast, since result is int

Example 2

char ch1 = 'A';
int val = ch1 + 1; // 'A' (65) + 1 = 66
System.out.println(val); // prints 66

Example 3

System.out.println(10 / 3);  // 3
System.out.println(10.0 / 3); // 3.3333333

TIP

When integer division occurs, fractional part is truncated. Use double or float for precise division.

2.8.2 String Concatenation Operator

+ is also used for string concatenation in Java.

String name = "Java";
String version = "17";
System.out.println(name + " " + version);

Output:

Java 17

INFO

If any operand in an expression is a String, the rest are converted to String automatically.

Example

System.out.println("Sum: " + 10 + 20);   // Sum: 1020
System.out.println(10 + 20 + " is sum"); // 30 is sum

2.8.3 Assignment Operators

Assignment operators assign values to variables.

Operator	Example	Equivalent
=	a = b	Assign b to a
+=	a += b	a = a + b
-=	a -= b	a = a - b
*=	a *= b	a = a * b
/=	a /= b	a = a / b
%=	a %= b	a = a % b

int x = 10;
x += 5;  // 15
x *= 2;  // 30

2.8.4 Increment & Decrement Operators

Operator	Description
++	Increment by 1
--	Decrement by 1

These can be prefix or postfix:

int a = 5;
System.out.println(++a); // 6 (increment, then print)
System.out.println(a++); // 6 (print, then increment)
System.out.println(a);   // 7

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++ and -- can only be applied to variables, not constants or expressions.

2.8.5 Relational Operators

Used to compare two values and return a boolean result.

Operator	Description
==	Equal to
!=	Not equal to
>	Greater than
<	Less than
>=	Greater or equal
<=	Less or equal

int a = 5, b = 10;
System.out.println(a < b); // true
System.out.println(a == b); // false

2.8.6 Logical Operators

Used to combine or invert boolean expressions.

Operator	Description
&&	Logical AND
`		`	Logical OR
!	Logical NOT

boolean x = true, y = false;
System.out.println(x && y); // false
System.out.println(x || y); // true
System.out.println(!x);     // false

WARNING

Logical AND (&&) and OR (||) short-circuit — meaning the second operand may not be evaluated if the result is already determined.

2.8.7 new Operator

The new operator is used to create objects in Java.

String s = new String("Hello");
Hello h = new Hello();

• Allocates memory for the object.
• Returns the reference (address) to the variable.

2.8.8 instanceof Operator

Checks whether an object is an instance of a specific class or subclass.

String s = "Hello";
System.out.println(s instanceof String); // true

2.8.9 Conditional (Ternary) Operator

Ternary operator ?: is a shorthand for if-else.

int a = 10, b = 20;
int max = (a > b) ? a : b;
System.out.println(max);

Equivalent to:

if (a > b)
  max = a;
else
  max = b;

2.8.10 Bitwise Operators

Operate at the bit level for integral data types.

Operator	Description
&	Bitwise AND
`	`	Bitwise OR
^	Bitwise XOR
~	Bitwise Complement
<<	Left Shift
>>	Right Shift
>>>	Unsigned Right Shift

int a = 5, b = 3;
System.out.println(a & b);  // 1
System.out.println(a | b);  // 7
System.out.println(a ^ b);  // 6
System.out.println(~a);     // -6

Shift Operators Example

int a = 8;
System.out.println(a << 1); // 16 (multiply by 2)
System.out.println(a >> 1); // 4  (divide by 2)

⚙️ Operator Precedence (Highest → Lowest)

Precedence	Operators	Description
1	()	Parentheses
2	++, --, !, ~	Unary
3	*, /, %	Multiplicative
4	+, -	Additive
5	<<, >>, >>>	Shift
6	<, >, <=, >=, instanceof	Relational
7	==, !=	Equality
8	&	Bitwise AND
9	^	Bitwise XOR
10	`	`	Bitwise OR
11	&&	Logical AND
12	`		`	Logical OR
13	?:	Conditional
14	=, +=, -=, *=, /=, %=	Assignment

💡 Summary – Operators

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Key Takeaways

1. Operators are categorized by operation and number of operands.
2. Arithmetic operations result in int or wider type.
3. String concatenation uses +.
4. Compound assignment automatically performs type conversion.
5. ++ and -- work only on variables.
6. == compares values; equals() compares content (for objects).
7. Logical operators short-circuit.
8. Bitwise operators manipulate individual bits.
9. instanceof checks runtime type.
10. Use parentheses () to control precedence.

📘 Practice Questions

1. What are the different types of operators in Java?
2. What is the difference between unary and binary operators?
3. How does Java handle division between two integers?
4. What is the result of "A" + 10 + 20 vs 10 + 20 + "A"?
5. What’s the purpose of compound assignment operators?
6. How do pre- and post-increment differ?
7. What is short-circuit evaluation?
8. How does the instanceof operator work?
9. How do bitwise and logical operators differ?
10. Arrange the operators in decreasing order of precedence.

✅ Module Summary

• Character sets, identifiers, and data types define Java’s core syntax.
• Variables and constants control data storage.
• Literals represent values directly in code.
• Operators enable all mathematical, logical, and object-based operations.