Java for Beginners
Tags: java, beginners, tutorial, programming
Published: 2023-09-27 11:07:23

Java is a versatile and widely-used programming language known for its portability and platform independence. In this Markdown document, we will explore various Java concepts with a plethora of real-world examples to help you understand the language better.

## Table of Contents

1. [Hello, World!](#hello-world)
2. [Variables and Data Types](#variables-and-data-types)
3. [Conditional Statements](#conditional-statements)
4. [Loops](#loops)
5. [Arrays](#arrays)
6. [Functions (Methods)](#functions-methods)
7. [Object-Oriented Programming](#object-oriented-programming)
8. [File Handling](#file-handling)

---

## Hello, World!

```java
public class HelloWorld {
    public static void main(String[] args) {
        // This is a simple Java program that prints "Hello, World!" to the console.
        System.out.println("Hello, World!");
    }
}
```

In this example, we have a Java program that consists of a class named `HelloWorld`. The `main` method is the entry point for the program, and it prints "Hello, World!" to the console using `System.out.println`.

## Variables and Data Types

```java
public class VariablesExample {
    public static void main(String[] args) {
        // Declare and initialize variables
        int age = 25;
        double salary = 50000.50;
        String name = "John Doe";

        // Print variable values
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Salary: " + salary);
    }
}
```

In this example, we declare and initialize variables of different data types (`int`, `double`, and `String`). Then, we print the values of these variables to the console.

## Conditional Statements (If-Else Statement)

```java
public class IfElseExample {
    public static void main(String[] args) {
        // Define an age
        int age = 18;
        
        // Check if the age is greater than or equal to 18
        if (age >= 18) {
            System.out.println("You are an adult.");
        } else {
            System.out.println("You are not yet an adult.");
        }
    }
}
```

In this example, we use an `if-else` statement to check whether a person is an adult based on their age. If the `age` is greater than or equal to 18, it prints "You are an adult"; otherwise, it prints "You are not yet an adult."

## Loops (For Loop)

```java
public class ForLoopExample {
    public static void main(String[] args) {
        // Use a for loop to count from 1 to 5
        for (int i = 1; i <= 5; i++) {
            System.out.println("Count: " + i);
        }
    }
}
```

This example demonstrates a `for` loop that counts from 1 to 5 and prints the count at each iteration. The loop initializes `i` to 1, continues as long as `i` is less than or equal to 5, and increments `i` by 1 in each iteration.

## Loops (While Loop)

```java
public class WhileLoopExample {
    public static void main(String[] args) {
        // Use a while loop to count from 1 to 5
        int i = 1;
        while (i <= 5) {
            System.out.println("Count: " + i);
            i++;
        }
    }
}
```

This example uses a `while` loop to achieve the same counting from 1 to 5 as the previous example. It initializes `i` to 1, and the loop continues as long as `i` is less than or equal to 5. In each iteration, it prints the count and increments `i`.

## Arrays

```java
public class ArrayExample {
    public static void main(String[] args) {
        // Declare and initialize an integer array
        int[] numbers = {1, 2, 3, 4, 5};

        // Access and print array elements
        System.out.println("Element at index 0: " + numbers[0]);
        System.out.println("Element at index 2: " + numbers[2]);
        
        // Calculate and print the length of the array
        int length = numbers.length;
        System.out.println("Array length: " + length);
    }
}
```

In this example, we declare and initialize an integer array called `numbers`. We access and print specific elements of the array using their indices (e.g., `numbers[0]` and `numbers[2]`). We also calculate and print the length of the array using `numbers.length`.

## Functions (Methods)

```java
public class MethodsExample {
    // Define a method to calculate the sum of two numbers
    public static int add(int a, int b) {
        return a + b;
    }

    public static void main(String[] args) {
        // Call the 'add' method and print the result
        int result = add(5, 3);
        System.out.println("Sum: " + result);
    }
}
```

In this example, we define a method (`add`) that takes two integer parameters and returns their sum. In the `main` method, we call the `add` method with values `5` and `3`, and then we print the result.

## Object-Oriented Programming (Classes and Objects)

```java
// Define a class named 'Person'
class Person {
    String name;
    int age;

    // Constructor to initialize 'name' and 'age'
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // Method to display person information
    public void displayInfo() {
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
    }
}

public class OOPExample {
    public static void main(String[] args) {
        // Create objects of the 'Person' class
        Person person1 = new Person("Alice", 25);
        Person person2 = new Person("Bob", 30);

        // Call the 'displayInfo' method for each person
        person1.displayInfo();
        person2.displayInfo();
    }
}
```

In this example, we define a class called `Person` with attributes (`name` and `age`) and a constructor to initialize them. We also define a method (`displayInfo`) to display the person's information. In the `main` method, we create two `Person` objects, set their attributes, and call the `displayInfo` method for each object.

## File Handling (Reading and Writing)

```java
import java.io.*;
public class FileHandlingExample {
    public static void main(String[] args) {
        try {
            // Create a FileWriter to write to a file
            FileWriter writer = new FileWriter("sample.txt");
            writer.write("Hello, File Handling!");
            writer.close();

            // Create a FileReader to read from the file
            FileReader reader = new FileReader("sample.txt");
            int character;
            while ((character = reader.read()) != -1) {
                System.out.print((char) character);
            }
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
```

In this example, we demonstrate basic file handling in Java. We use a `FileWriter` to write the string "Hello, File Handling!" to a file named "sample.txt" and a `FileReader` to read and print the contents of the same file.

These additional examples cover arrays, methods, object-oriented programming (classes and objects), and file handling in Java. If you have any specific questions or if you'd like to see more examples related to a particular topic, please feel free to ask.