Java Basics: Encryption and Multiplication Table Examples for Beginners

1. Translation Cipher (shift by 4)

The program implements a simple substitution cipher that shifts each alphabetic character forward by four positions in the English alphabet, wrapping around at the end. Non‑alphabetic characters are left unchanged. Example: A → E, a → e, 1 → 1.

public class Encryption {
    public static void main(String[] args) {
        char[] arr = {'I',' ','l','o','v','e',' ','y','o','u','!'};
        System.out.println("Before encryption:");
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i]);
        }
        System.out.println();
        System.out.println("After encryption:");
        for (int i = 0; i < arr.length; i++) {
            int val = arr[i];
            if ((val >= 'a' && val <= 'z') || (val >= 'A' && val <= 'Z')) {
                val = val + 4;
                // wrap around if past 'Z' or 'z'
                if ((val > 'Z' && val <= 'Z' + 4) || val > 'z') {
                    val = val - 26;
                }
                System.out.print((char) val);
            } else {
                System.out.print(arr[i]);
            }
        }
        System.out.println();
    }
}

Running the program prints the original string I love you! and the encrypted result M pszi csy!. The logic distinguishes uppercase and lowercase letters because their ASCII ranges differ, adds 4 to the code point, and subtracts 26 when the result exceeds the alphabet range.

public class Decryption {
    public static void main(String[] args) {
        char[] arr = {'M',' ','p','s','z','i',' ','c','s','y','!'};
        System.out.println("Before decryption:");
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i]);
        }
        System.out.println();
        System.out.println("After decryption:");
        for (int i = 0; i < arr.length; i++) {
            int val = arr[i];
            if ((val >= 'a' && val <= 'z') || (val >= 'A' && val <= 'Z')) {
                val = val - 4;
                // wrap around if before 'A' or 'a'
                if ((val < 'a' && val >= 'a' - 4) || val < 'A') {
                    val = val + 26;
                }
                System.out.print((char) val);
            } else {
                System.out.print(arr[i]);
            }
        }
        System.out.println();
    }
}

The decryption restores the original text I love you! by reversing the shift and applying the same wrap‑around logic.

2. 9×9 Multiplication Table

A double for loop prints the classic multiplication table in a triangular layout. The outer loop iterates rows from 1 to 9; the inner loop iterates columns from 1 up to the current row index, ensuring j <= i so that each row contains only the products up to its diagonal.

public class MultiplicationTable {
    public static void main(String[] args) {
        for (int i = 1; i <= 9; i++) { // rows
            for (int j = 1; j <= i; j++) { // columns up to current row
                System.out.print(j + "*" + i + "=" + (i * j));
                // add a space for alignment; single‑digit results get an extra space
                if (i * j < 10) {
                    System.out.print("  ");
                } else {
                    System.out.print(" ");
                }
            }
            System.out.println();
        }
    }
}

Sample output (first three rows) demonstrates the triangular shape:

1*1=1  
1*2=2  2*2=4  
1*3=3  2*3=6  3*3=9  
...

The condition j <= i is essential for producing the near‑triangular format of the 9×9 table.