Java Tutorial

Java is a widely-used, object-oriented programming language that is designed to be platform-independent, robust, and secure. In this tutorial, we'll cover the essential concepts and features of Java, providing you with a solid foundation to start programming in Java.

1. Introduction to Java

Java was created by James Gosling and Mike Sheridan at Sun Microsystems (which is now owned by Oracle). It is based on the idea of "write once, run anywhere," meaning that Java programs can run on any device that supports the Java Virtual Machine (JVM).

Key Features of Java:

• Object-Oriented: Everything in Java is an object, making the language more modular and flexible.

• Platform-Independent: Java programs can run on any operating system with the JVM.

• Automatic Memory Management: Java has a built-in garbage collector that automatically manages memory.

• Multithreaded: Java supports multithreading, allowing you to perform multiple tasks at once.

• Robust and Secure: Java has built-in mechanisms for error handling and security.

2. Setting Up Java

To start writing and running Java code, you need to set up the Java Development Kit (JDK). Here's how to set up Java:

1. Download JDK:

   • Go to the Oracle website and download the appropriate version of JDK for your operating system.

2. Install JDK:

   • Follow the installation instructions for your operating system.

3. Set Up Environment Variables (for command-line use):

   • Set the JAVA_HOME environment variable to the JDK installation directory.

   • Add the bin directory of JDK to your PATH.

4. Verify Installation:

   • Open a command prompt or terminal and type:

     java -version

     This should display the installed version of Java.

3. Writing Your First Java Program

Your first Java program is typically a simple "Hello, World!" program. This program outputs the text "Hello, World!" to the console.

Code Example:

public class HelloWorld {    public static void main(String[] args) {        // Print Hello, World! to the console        System.out.println("Hello, World!");    }}

• public class HelloWorld: This defines a class named HelloWorld.

• public static void main(String[] args): This is the main method, which serves as the entry point of any Java program.

• System.out.println("Hello, World!"): This prints "Hello, World!" to the console.

Steps to Run the Program:

1. Save the code in a file called HelloWorld.java.

2. Open a command prompt or terminal, navigate to the directory where the file is saved, and compile the program:

   javac HelloWorld.java

3. After successful compilation, run the program using the command:

   java HelloWorld

4. Java Syntax

Java has a very specific syntax that must be followed. Here's an overview of some fundamental syntax rules:

• Class and Method Names: Java class names typically start with an uppercase letter (CamelCase). Method names begin with a lowercase letter.

  Example:

  public class MyClass {    public void myMethod() {        // Method logic    }}

• Statements: Every statement in Java ends with a semicolon ;.

• Braces: Blocks of code are enclosed in curly braces { }.

• Variables: Variables must be declared with a specific type (e.g., int, String, boolean).

  Example:

  int number = 10;String message = "Hello!";

5. Variables and Data Types

Java has two types of data types:

1. Primitive Data Types: These are basic types.

   • int: Integer values (e.g., 5, -10)

   • double: Decimal numbers (e.g., 10.5, -3.14)

   • char: Single characters (e.g., 'A', 'b')

   • boolean: True or false values (true, false)

   • byte, short, long, float are also primitive types.

2. Reference Data Types: These hold references to objects or arrays.

   • String: A sequence of characters (e.g., "Hello")

   • Arrays, Classes, Interfaces

Example:

int age = 30;double price = 15.75;char grade = 'A';boolean isStudent = true;String name = "Alice";

6. Control Flow in Java

Control flow statements allow you to control the flow of execution in your program.

If-Else Statement

int age = 18;if (age >= 18) {    System.out.println("You are an adult.");} else {    System.out.println("You are a minor.");}

Switch Statement

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

For Loop

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

While Loop

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

7. Functions (Methods) in Java

In Java, functions are called methods. Methods are blocks of code that perform a specific task.

Method Declaration:

public returnType methodName(parameters) {    // Method body}

• public: Access modifier (can be private, protected, or default).

• returnType: The data type of the return value (e.g., int, String).

• methodName: The name of the method.

• parameters: The inputs that the method takes (optional).

Example:

public class Calculator {    public int add(int a, int b) {        return a + b;    }    public static void main(String[] args) {        Calculator calc = new Calculator();        System.out.println(calc.add(10, 5));  // Output: 15    }}

8. Object-Oriented Programming (OOP) Concepts

Java is an object-oriented programming language, which means that it is centered around objects that have both state (attributes) and behavior (methods).

Classes and Objects

• Class: A blueprint for creating objects.

• Object: An instance of a class.

Example:

class Car {    String brand;    int year;    void displayInfo() {        System.out.println("Brand: " + brand + ", Year: " + year);    }}public class Main {    public static void main(String[] args) {        Car myCar = new Car();        myCar.brand = "Toyota";        myCar.year = 2020;        myCar.displayInfo();  // Output: Brand: Toyota, Year: 2020    }}

Encapsulation

Encapsulation is the technique of bundling the data (attributes) and the methods that operate on the data into a single unit (class). It also helps in restricting access to certain components of the object.

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

9. Inheritance in Java

Inheritance allows one class to inherit fields and methods from another class.

class Animal {    void sound() {        System.out.println("Animal makes a sound");    }}class Dog extends Animal {    void sound() {        System.out.println("Dog barks");    }}public class Main {    public static void main(String[] args) {        Dog dog = new Dog();        dog.sound();  // Output: Dog barks    }}

10. Java Collections Framework

Java provides a set of classes and interfaces for storing and manipulating data. These classes are part of the Collections Framework, which includes:

• List (e.g., ArrayList, LinkedList)

• Set (e.g., HashSet, TreeSet)

• Map (e.g., HashMap, TreeMap)

Example using ArrayList:

import java.util.ArrayList;public class Main {    public static void main(String[] args) {        ArrayList<String> fruits = new ArrayList<>();        fruits.add("Apple");        fruits.add("Banana");        fruits.add("Orange");        System.out.println(fruits);  // Output: [Apple, Banana, Orange]    }}

11. Exception Handling

Java provides a robust exception-handling mechanism using try, catch, and finally blocks to handle runtime errors.

public class Main {    public static void main(String[] args) {        try {            int result = 10 / 0;  // Will throw an ArithmeticException        } catch (ArithmeticException e) {            System.out.println("Error: Division by zero");        } finally {            System.out.println("This block is always executed");        }    }}

12. Multithreading in Java

Java provides built-in support for multithreading, allowing multiple threads to run concurrently.

class MyThread extends Thread {    public void run() {        System.out.println(Thread.currentThread().getName() + " is running");    }}public class Main {    public static void main(String[] args) {        MyThread t1 = new MyThread();        MyThread t2 = new MyThread();        t1.start();  // Starts t1 thread        t2.start();  // Starts t2 thread    }}

Conclusion

This Java tutorial has covered the basics of Java programming, including setting up Java, writing a simple program, and understanding key concepts such as variables, control flow, methods, object-oriented programming, and multithreading. Java is a vast language, and as you gain experience, you'll be able to explore more advanced topics and libraries.

Let me know if you'd like to dive deeper into any specific topic!