java chapter 2

🔹 1. Building Blocks of Java Program

Every Java program is made up of:

• Keywords – Reserved words with special meaning (e.g., int, class, if, for).
• Identifiers – Names for variables, methods, classes, etc.
  ✅ Must start with a letter, _, or $; can’t use spaces or keywords.
• Literals – Constant values (like 10, 'A', "Hello").
• Operators – Symbols to perform operations (like +, -, ==).
• Separators – (), {}, [], ;, ,, . etc.

---

🔹 2. Data Types in Java

Java is a strongly typed language — every variable must have a declared type.

A. Primitive Data Types

Type	Size	Example	Description
byte	1 byte	127	small integers
short	2 bytes	32000	medium integers
int	4 bytes	100000	default integer type
long	8 bytes	10000000000L	large integers
float	4 bytes	10.5f	decimal numbers (less precision)
double	8 bytes	12.345	decimal numbers (more precision)
char	2 bytes	‘A’	single character
boolean	1 bit	true / false	logical value

B. Non-Primitive Data Types

• String, Arrays, Classes, Interfaces, Objects etc.

---

🔹 3. Variables

A variable is a name that refers to a memory location storing data.

Syntax:

int age = 18;

Types of Variables:

1. Local Variable – Declared inside a method.
2. Instance Variable – Declared inside a class but outside any method.
3. Static Variable – Declared using static keyword; shared by all objects.

Rules for Naming:

• Must start with letter, $, or _.
• No spaces or keywords.
• Case-sensitive (Age ≠ age).

---

🔹 4. Constants

• Declared using the final keyword.
  Example:final double PI = 3.14159;
• Once assigned, their value cannot be changed.

---

🔹 5. Type Casting

Changing one data type into another.

Types:

1. Implicit (Automatic) – Smaller → larger type
   Example:int a = 10; double b = a; // int to double
2. Explicit (Manual) – Larger → smaller type
   Example:double x = 9.8; int y = (int) x; // double to int

---

🔹 6. Operators in Java

A. Arithmetic Operators

+, -, *, /, %

B. Relational Operators

==, !=, >, <, >=, <=

C. Logical Operators

&&, ||, !

D. Assignment Operators

=, +=, -=, *=, /=, %=

E. Unary Operators

++ (increment), -- (decrement)

F. Conditional (Ternary) Operator

condition ? value_if_true : value_if_false

Example:

int max = (a > b) ? a : b;

G. Bitwise Operators

Operate on bits: &, |, ^, ~, <<, >>, >>>

---

🔹 7. Expressions and Type Promotion

• If different data types are used in an expression, Java promotes smaller types to a larger type automatically.
  Example:

int a = 5;
float b = 6.2f;
float c = a + b;   // a converted to float

---

🔹 8. Comments in Java

Used to improve readability.

// Single-line comment
/* Multi-line
   comment */

---