Basic JAVA tutorial with code examples

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 Certainly! Below is a comprehensive tutorial on Java, covering key concepts, examples, and code snippets to help you understand Java programming in detail. I will break this tutorial into several sections, starting from the basics and moving into more advanced topics.

1. Introduction to Java

Java is a high-level, object-oriented programming language designed for portability, performance, and security. It was created by James Gosling and Mike Sheridan at Sun Microsystems in 1995.

Key Features:

  • Object-Oriented: Everything in Java is an object.
  • Platform Independent: Write once, run anywhere (thanks to the Java Virtual Machine, JVM).
  • Simple and Robust: Java is designed to be easy to learn and provides automatic memory management (garbage collection).
  • Secure: Java is designed with security in mind, especially for online applications.

2. Setting Up the Java Environment

To get started with Java, you need to install the following:

  1. JDK (Java Development Kit): Contains tools necessary to write Java programs.
  2. IDE (Integrated Development Environment): Examples include Eclipse, IntelliJ IDEA, and NetBeans.

You can download the JDK from the official Oracle website: JDK Downloads.

3. Java Basic Syntax and Structure

3.1 Hello World Program

The simplest Java program is the "Hello World" program. Here is how it looks:

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

Explanation:

  • public class HelloWorld: Defines a class named HelloWorld.
  • public static void main(String[] args): The main method, where the program starts execution.
  • System.out.println(): A method that prints output to the console.

3.2 Data Types

Java has a rich set of data types, both primitive and reference types.

Primitive Data Types:

  • int: Integer numbers
  • float: Floating-point numbers
  • double: Double precision floating-point numbers
  • char: Single character
  • boolean: True or false values

Example:

int x = 10;
double y = 5.5;
char letter = 'A';
boolean isJavaFun = true;

Reference Data Types:

  • String: A sequence of characters.
  • Arrays, Classes, Interfaces, etc.

Example:

String name = "Java";

4. Variables and Operators

4.1 Variables

In Java, a variable is a container for storing data values. It must be declared with a type before use.

Example:


int age = 25; // Declaring and initializing an integer variable
String name = "John"; // Declaring and initializing a string variable

4.2 Operators

Java supports a variety of operators like arithmetic, relational, logical, etc.

  • Arithmetic Operators: +, -, *, /, %
  • Relational Operators: ==, !=, <, >, <=, >=
  • Logical Operators: &&, ||, !
  • Assignment Operator: =

Example:

int a = 5;
int b = 2;
int sum = a + b; // Arithmetic operator
boolean isEqual = (a == b); // Relational operator
boolean result = (a > b && b > 0); // Logical operator

5. Control Flow Statements

5.1 Conditional Statements

Java uses if, else if, and else for conditional execution.

Example:

int age = 20;

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

5.2 Switch-Case

The switch statement evaluates an expression and executes the corresponding case block.

Example:

int day = 3;
switch (day) {
    case 1:
        System.out.println("Monday");
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    case 3:
        System.out.println("Wednesday");
        break;
    default:
        System.out.println("Invalid day");
}

5.3 Loops

Java supports several types of loops: for, while, and do-while.

For Loop Example:

for (int i = 1; i <= 5; i++) {
    System.out.println(i);
}

While Loop Example:


int i = 1;
while (i <= 5) {
    System.out.println(i);
    i++;
}

Do-While Loop Example:

int i = 1;
do {
    System.out.println(i);
    i++;
} while (i <= 5);

6. Functions (Methods)

A method in Java is a block of code that performs a specific task. It is defined within a class and can be called to execute the task.

6.1 Method Definition

public class Calculator {

    public static int add(int a, int b) {
        return a + b;
    }

    public static void main(String[] args) {
        int result = add(5, 3); // Calling the add method
        System.out.println("Result: " + result);
    }
}

Explanation:

  • public static int add(int a, int b): A method that takes two integers and returns their sum.
  • main: The entry point of the program.

6.2 Method Overloading

Java allows methods with the same name but different parameters.

class Display {

    public void show(int num) {
        System.out.println("Integer: " + num);
    }

    public void show(String str) {
        System.out.println("String: " + str);
    }

    public static void main(String[] args) {
        Display display = new Display();
        display.show(10);  // Calls show(int)
        display.show("Hello");  // Calls show(String)
    }
}

7. Object-Oriented Programming (OOP) Concepts

7.1 Classes and Objects

Java is object-oriented, meaning it revolves around classes and objects. A class is a blueprint, and an object is an instance of that class.

class Car {
    String model;
    int year;

    public void displayInfo() {
        System.out.println("Model: " + model + ", Year: " + year);
    }
}

public class Main {
    public static void main(String[] args) {
        Car car = new Car();  // Creating an object
        car.model = "Toyota";
        car.year = 2020;
        car.displayInfo();  // Calling a method of the object
    }
}

7.2 Inheritance

Inheritance allows one class to inherit properties and behaviors 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();  // Calls Dog's overridden method
    }
}

7.3 Polymorphism

Polymorphism allows methods to have the same name but behave differently based on the object type.

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

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

class Cat extends Animal {
    void sound() {
        System.out.println("Cat meows");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal myDog = new Dog();  // Animal reference but Dog object
        Animal myCat = new Cat();  // Animal reference but Cat object

        myDog.sound();  // Calls Dog's sound
        myCat.sound();  // Calls Cat's sound
    }
}

8. Exception Handling

In Java, exceptions are used to handle errors or other exceptional conditions.

8.1 Try-Catch Block

public class Main {
    public static void main(String[] args) {
        try {
            int result = 10 / 0;  // This will throw an exception
        } catch (ArithmeticException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

8.2 Throw and Throws

You can use throw to throw an exception manually and throws to declare exceptions in a method.

class CustomException extends Exception {
    public CustomException(String message) {
        super(message);
    }
}

public class Main {
    public static void checkAge(int age) throws CustomException {
        if (age < 18) {
            throw new CustomException("Age must be 18 or older");
        }
    }

    public static void main(String[] args) {
        try {
            checkAge(16);
        } catch (CustomException e) {
            System.out.println("Caught exception: " + e.getMessage());
        }
    }
}

9. Java Collections

The Java Collections Framework provides classes and interfaces for working with data groups, such as ArrayList, HashSet, HashMap, etc.

9.1 ArrayList

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("Apple");
        list.add("Banana");
        list.add("Orange");

        for (String fruit : list) {
            System.out.println(fruit);
        }
    }
}

9.2 HashMap

import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        HashMap<String, String> map = new HashMap<>();
        map.put("1", "Apple");
        map.put("2", "Banana");
        map.put("3", "Orange");

        System.out.println("Fruit with key 2: " + map.get("2"));
    }
}

10. Conclusion

Java is a powerful and versatile language with vast capabilities, from basic syntax to advanced concepts such as object-oriented programming, exception handling, and collections. This tutorial has covered key areas, but Java is a deep language with endless possibilities.

Feel free to experiment with these examples and continue learning by exploring more advanced topics such as threads, file I/O, GUI programming, and networking. Happy coding!

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