Java Virtual Machine (JVM)

Java Virtual Machine (JVM)

• Converts compiled byte code into machine code.

• Allows Java programs to run on any platform (Write once, run anywhere).

• Byte code is OS-independent.

Parts of a Java Program:

1. Documentation Section:

• Comments about the program, author, date, purpose, etc.

2. Package Declaration:

• Organizes classes and avoids name conflicts.

• Example: package com.example.app;

3. Import Statements:

• Imports external classes.

• Example: import java.util.Scanner;

4. Class Definition:

• Contains class name, variables, and methods.

• Example: public class Rectangle { ... }

5. Variables:

• Class/Static Variables – shared by all objects.

• Instance/Object Variables – unique to each object.

• Local Variables – declared inside methods.

6. Main Method:

• Entry point of every Java program.

• Syntax: public static void main(String[] args) { ... }

7. Methods/Behaviors:

• Define actions the object can perform.

• Syntax: public int calculateArea(int width, int height) { ... }

Naming Conventions in Java

• Class Names: PascalCase → MyClass, StudentRecord

• Interfaces: PascalCase, often ends with Interface

• Methods: camelCase, verbs → getName(), calculateTotal()

• Variables: camelCase, nouns → userName, price

Constants: UPPERCASE_WITH_UNDERSCORES → PI, MAX_SIZE