Change project structure to a Maven Java project + Refactor (#2816)

src/main/java/com/thealgorithms/ciphers/Caesar.java

@@ -0,0 +1,118 @@
+package com.thealgorithms.ciphers;
+
+import java.util.Scanner;
+
+/**
+ * A Java implementation of Caesar Cipher. /It is a type of substitution cipher
+ * in which each letter in the plaintext is replaced by a letter some fixed
+ * number of positions down the alphabet. /
+ *
+ * @author FAHRI YARDIMCI
+ * @author khalil2535
+ */
+public class Caesar {
+
+    /**
+     * Encrypt text by shifting every Latin char by add number shift for ASCII
+     * Example : A + 1 -> B
+     *
+     * @return Encrypted message
+     */
+    public static String encode(String message, int shift) {
+        StringBuilder encoded = new StringBuilder();
+
+        shift %= 26;
+
+        final int length = message.length();
+        for (int i = 0; i < length; i++) {
+
+            //            int current = message.charAt(i); //using char to shift characters because ascii
+            // is in-order latin alphabet
+            char current = message.charAt(i); // Java law : char + int = char
+
+            if (IsCapitalLatinLetter(current)) {
+
+                current += shift;
+                encoded.append((char) (current > 'Z' ? current - 26 : current)); // 26 = number of latin letters
+
+            } else if (IsSmallLatinLetter(current)) {
+
+                current += shift;
+                encoded.append((char) (current > 'z' ? current - 26 : current)); // 26 = number of latin letters
+
+            } else {
+                encoded.append(current);
+            }
+        }
+        return encoded.toString();
+    }
+
+    /**
+     * Decrypt message by shifting back every Latin char to previous the ASCII
+     * Example : B - 1 -> A
+     *
+     * @return message
+     */
+    public static String decode(String encryptedMessage, int shift) {
+        StringBuilder decoded = new StringBuilder();
+
+        shift %= 26;
+
+        final int length = encryptedMessage.length();
+        for (int i = 0; i < length; i++) {
+            char current = encryptedMessage.charAt(i);
+            if (IsCapitalLatinLetter(current)) {
+
+                current -= shift;
+                decoded.append((char) (current < 'A' ? current + 26 : current)); // 26 = number of latin letters
+
+            } else if (IsSmallLatinLetter(current)) {
+
+                current -= shift;
+                decoded.append((char) (current < 'a' ? current + 26 : current)); // 26 = number of latin letters
+
+            } else {
+                decoded.append(current);
+            }
+        }
+        return decoded.toString();
+    }
+
+    /**
+     * @return true if character is capital Latin letter or false for others
+     */
+    private static boolean IsCapitalLatinLetter(char c) {
+        return c >= 'A' && c <= 'Z';
+    }
+
+    /**
+     * @return true if character is small Latin letter or false for others
+     */
+    private static boolean IsSmallLatinLetter(char c) {
+        return c >= 'a' && c <= 'z';
+    }
+
+    public static void main(String[] args) {
+        Scanner input = new Scanner(System.in);
+        System.out.println("Please enter the message (Latin Alphabet)");
+        String message = input.nextLine();
+        System.out.println(message);
+        System.out.println("Please enter the shift number");
+        int shift = input.nextInt() % 26;
+        System.out.println("(E)ncode or (D)ecode ?");
+        char choice = input.next().charAt(0);
+        switch (choice) {
+            case 'E':
+            case 'e':
+                System.out.println(
+                        "ENCODED MESSAGE IS \n" + encode(message, shift)); // send our function to handle
+                break;
+            case 'D':
+            case 'd':
+                System.out.println("DECODED MESSAGE IS \n" + decode(message, shift));
+            default:
+                System.out.println("default case");
+        }
+        input.close();
+    }
+}