Basic Java Program Examples with Explanation

Here are some simple Java program examples with explanations:

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1. Hello, World Program

This is the most basic Java program that prints "Hello, World!" to the console.

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

Explanation:

• public class HelloWorld: Defines the class named HelloWorld.
• public static void main(String[] args): This is the entry point of the program. The main method is executed when the program runs.
• System.out.println("Hello, World!");: Prints the text to the console.

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2. Sum of Two Numbers

This program takes two numbers and calculates their sum.

import java.util.Scanner;

public class SumTwoNumbers {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter the first number: ");
        int num1 = scanner.nextInt();

        System.out.print("Enter the second number: ");
        int num2 = scanner.nextInt();

        int sum = num1 + num2;
        System.out.println("The sum is: " + sum);

        scanner.close();
    }
}

Explanation:

• Scanner scanner = new Scanner(System.in);: Creates an Scanner object to read input from the user.
• nextInt(): Reads an integer input.
• int sum = num1 + num2;: Adds the two numbers.
• scanner.close();: Closes the scanner to free resources.

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3. Check if a Number is Even or Odd

This program determines if a given number is even or odd.

import java.util.Scanner;

public class EvenOdd {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a number: ");
        int num = scanner.nextInt();

        if (num % 2 == 0) {
            System.out.println(num + " is Even.");
        } else {
            System.out.println(num + " is Odd.");
        }

        scanner.close();
    }
}

Explanation:

• if (num % 2 == 0): Checks if the number is divisible by 2 (even).
• else: Executes if the number is not even, indicating it is odd.

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4. Factorial of a Number

This program calculates the factorial of a number using a loop.

import java.util.Scanner;

public class Factorial {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a number: ");
        int num = scanner.nextInt();

        int factorial = 1;
        for (int i = 1; i <= num; i++) {
            factorial *= i;
        }

        System.out.println("The factorial of " + num + " is " + factorial);

        scanner.close();
    }
}

Explanation:

• for (int i = 1; i <= num; i++): Loops from 1 to the input number.
• factorial *= i;: Multiplies factorial by the current value of i in each iteration.

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5. Prime Number Check

This program checks if a number is prime.

import java.util.Scanner;

public class PrimeCheck {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a number: ");
        int num = scanner.nextInt();

        boolean isPrime = true;

        if (num <= 1) {
            isPrime = false;
        } else {
            for (int i = 2; i <= Math.sqrt(num); i++) {
                if (num % i == 0) {
                    isPrime = false;
                    break;
                }
            }
        }

        if (isPrime) {
            System.out.println(num + " is a prime number.");
        } else {
            System.out.println(num + " is not a prime number.");
        }

        scanner.close();
    }
}

Explanation:

• if (num % i == 0): Checks if num is divisible by i, indicating it's not prime.
• Math.sqrt(num): Optimizes the loop to run only up to the square root of num.

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6. Reverse a String

This program reverses an input string.

import java.util.Scanner;

public class ReverseString {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a string: ");
        String input = scanner.nextLine();

        String reversed = "";
        for (int i = input.length() - 1; i >= 0; i--) {
            reversed += input.charAt(i);
        }

        System.out.println("Reversed string: " + reversed);

        scanner.close();
    }
}

Explanation:

• input.length(): Gets the length of the string.
• input.charAt(i): Accesses the character at the ith position in the string.
• The loop iterates in reverse to build the reversed string.

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7. Fibonacci Sequence

This program generates the Fibonacci sequence up to n terms.

import java.util.Scanner;

public class Fibonacci {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter the number of terms: ");
        int n = scanner.nextInt();

        int a = 0, b = 1;
        System.out.print("Fibonacci Sequence: " + a + " " + b);

        for (int i = 3; i <= n; i++) {
            int next = a + b;
            System.out.print(" " + next);
            a = b;
            b = next;
        }

        scanner.close();
    }
}

Explanation:

• The first two terms of the Fibonacci sequence are 0 and 1.
• The next term is calculated by adding the previous two terms.

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These examples cover a range of common Java programming tasks. Let me know if you'd like more advanced examples! 😊