Complete Java Programming Notes: A Comprehensive Guide from Basics to Advanced

Java Programming Notes for IT Students

This guide covers key concepts in Java programming to help you develop into a professional Java developer. The topics are structured progressively, from the basics to advanced concepts, to ensure you have a solid foundation in Java development.

1. Introduction to Java

What is Java?

• Java is a high-level, object-oriented, and platform-independent programming language.
• It follows the Write Once, Run Anywhere principle, meaning code written on one platform can run on any other platform that supports Java.
• Java is widely used for building web applications, mobile applications (Android), enterprise systems, and more.

Key Features of Java

• Object-Oriented: Everything in Java is treated as an object, providing a clear structure to your code.
• Platform Independent: Java code is compiled to bytecode, which can be executed by any platform using the Java Virtual Machine (JVM).
• Robust: Java handles errors gracefully and provides automatic memory management through garbage collection.
• Multithreaded: Java provides built-in support for multithreading, allowing developers to write efficient programs that can handle multiple tasks simultaneously.
• Secure: Java has a built-in security model, ensuring that malicious code does not corrupt the system.

2. Java Basic Syntax

Structure of a Java Program

• Every Java program has at least one class, and inside the class, you define the main() method.

public class Main { public static void main(String[] args) { System.out.println("Hello, World!"); } }

Java Statements

• Statements are the smallest standalone elements in Java code.
• Variables are declared using data types, followed by the variable name.
• Semicolons are used to terminate statements.

3. Data Types and Variables

Primitive Data Types

• int: Stores integers (-2^31 to 2^31-1).
• double: Stores decimal values.
• char: Stores a single character.
• boolean: Stores true or false.
• byte, short, long: Used for small, medium, and large integers respectively.

Non-Primitive Data Types

• String: A sequence of characters.
• Arrays: A collection of elements of the same type.
• Classes: Custom data types defined by the programmer.

Variable Declaration and Initialization

int number = 10; // Integer declaration and initialization String name = "Java"; // String declaration and initialization

4. Control Flow

Conditional Statements

• if: Executes a block of code if the condition is true.

if (x > 10) { System.out.println("x is greater than 10"); }

• else if: Checks multiple conditions.

if (x > 10) { System.out.println("x is greater than 10"); } else if (x == 10) { System.out.println("x is equal to 10"); }

• else: Executes code if the previous conditions are false.

if (x > 10) { System.out.println("x is greater than 10"); } else { System.out.println("x is not greater than 10"); }

Switch Statement

The switch statement is an alternative to multiple if-else statements.

switch (day) { case 1: System.out.println("Monday"); break; case 2: System.out.println("Tuesday"); break; default: System.out.println("Invalid day"); }

Loops

• For Loop: Used when the number of iterations is known.

for (int i = 0; i < 5; i++) { System.out.println(i); }

• While Loop: Used when the number of iterations is not known.

int i = 0; while (i < 5) { System.out.println(i); i++; }

• Do-While Loop: Guarantees at least one iteration.

int i = 0; do { System.out.println(i); i++; } while (i < 5);

5. Object-Oriented Programming (OOP)

Classes and Objects

• Class: A blueprint for creating objects.
• Object: An instance of a class.

public class Car { String model; int year; public void displayInfo() { System.out.println("Model: " + model + ", Year: " + year); } } Car myCar = new Car(); myCar.model = "Toyota"; myCar.year = 2022; myCar.displayInfo();

Encapsulation

Encapsulation refers to bundling the data (variables) and the methods that operate on the data into a single unit (class).

• Use private access modifier for variables and provide public getter and setter methods.

public class Person { private String name; public String getName() { return name; } public void setName(String name) { this.name = name; } }

Inheritance

Inheritance allows a new class to inherit properties and behaviors from an existing class.

class Animal { void sound() { System.out.println("Animal makes a sound"); } } class Dog extends Animal { void sound() { System.out.println("Dog barks"); } }

Polymorphism

Polymorphism allows objects of different classes to be treated as objects of a common superclass.

• Method Overloading: Same method name, different parameter types.

class MathOperations { int add(int a, int b) { return a + b; } double add(double a, double b) { return a + b; } }

• Method Overriding: Subclass provides a specific implementation of a method inherited from the superclass.

Abstraction

Abstraction hides complex implementation details and shows only essential features.

abstract class Shape { abstract void draw(); } class Circle extends Shape { void draw() { System.out.println("Drawing Circle"); } }

6. Arrays

Declaring Arrays

Arrays are used to store multiple values of the same type in a single variable.

int[] arr = new int[5]; // Declares an array of 5 integers arr[0] = 10; // Access array elements

Array Initialization

int[] arr = {1, 2, 3, 4, 5}; // Initialize array with values

7. Exception Handling

Try-Catch Block

Exceptions are errors that occur during the execution of a program. Use try-catch to handle exceptions gracefully.

try { int result = 10 / 0; } catch (ArithmeticException e) { System.out.println("Error: " + e.getMessage()); }

Finally Block

The finally block is executed after try and catch blocks, regardless of whether an exception occurred.

try { // code } finally { // cleanup code }

8. Java Collections Framework

List Interface

• ArrayList: A resizable array implementation.

List list = new ArrayList<>(); list.add("Apple"); list.add("Banana");

Set Interface

• HashSet: A collection that does not allow duplicates.

Set set = new HashSet<>(); set.add("Apple"); set.add("Apple"); // Duplicates are not allowed

Map Interface

• HashMap: A collection of key-value pairs.

Map map = new HashMap<>(); map.put("Apple", 1); map.put("Banana", 2);

9. Multithreading

Thread Creation

In Java, you can create threads using the Thread class or by implementing the Runnable interface.

class MyThread extends Thread { public void run() { System.out.println("Thread is running"); } } MyThread t = new MyThread(); t.start();

10. Java Streams API

The Java Streams API allows you to process sequences of elements (like collections) in a functional style.

Example of Stream

List list = Arrays.asList("a", "b", "c", "d"); list.stream().filter(s -> s.startsWith("a")).forEach(System.out::println);

11. Java File I/O

Reading Files

import java.io.*; public class FileReaderExample { public static void main(String[] args) throws IOException { BufferedReader reader = new BufferedReader(new FileReader("file.txt")); String line; while ((line = reader.readLine()) != null) { System.out.println(line); } reader.close(); } }

Writing Files

import java.io.*; public class FileWriterExample { public static void main(String[] args) throws IOException { BufferedWriter writer = new BufferedWriter(new FileWriter("output.txt")); writer.write("Hello, World!"); writer.close(); } }

12. Java Best Practices

• Code Readability: Follow naming conventions (camelCase for variables, methods, PascalCase for classes).
• Code Documentation: Use comments and JavaDoc to document code for better understanding.
• Error Handling: Always handle exceptions and provide meaningful error messages.
• Use Design Patterns: Familiarize yourself with common design patterns like Singleton, Factory, Observer, etc.

Conclusion

Mastering Java involves understanding its syntax, object-oriented principles, error handling, and frameworks. By practicing consistently and exploring advanced concepts like multithreading and streams, you can become a professional Java developer. Keep building projects, explore libraries, and stay updated with new features in the Java ecosystem.