Update Caesar.java

ciphers/Caesar.java

@@ -1,117 +1,131 @@
-/**
-Author : FAHRI YARDIMCI
+package ciphers;
 
-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. /
-**/
 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 {
-public static String encode (String message,int shift)
-{
-	String encoded = "";
-	for(int i = 0 ; i<message.length() ;i++)
-	{
-		int current = message.charAt(i); //using char to shift characters because ascii is in-order latin alphabet
-		if(current==32)
-		{
-			encoded += " ";
-			continue;
-
-		}
-		else if (current>=65 && current<= 90)
-		{
-			int numAlphabet = message.charAt(i);
-			if(shift + numAlphabet > 90)
-			{
-				int j = 90 - numAlphabet;
-				char nextKey = (char)(65 + (shift - j - 1));
-				encoded += nextKey;
-
-			}
-			else
-			{
-				char nextKey = (char)(current + shift);
-				encoded += nextKey;
-			}
-		}
-		else if (current>=97 && current <= 122)
-		{
-			int numAlphabet = message.charAt(i);
-			if(shift + numAlphabet > 122)
-			{
-				int j = 122 - numAlphabet;
-				char nextKey = (char)(97 + (shift - j - 1));
-				encoded += nextKey;
-			}
-			else
-			{
-				char nextKey = (char)(current + shift);
-				encoded += nextKey;
-			}
-		}
-	}
-	return encoded;
-}
-public static String decode (String message,int shift)
-{
-	String decoded = "";
-	for(int i = 0 ; i<message.length() ;i++)
-	{
-		int current = message.charAt(i);
-		if(current==32)
-		{
-			decoded += " ";
-			continue;
-
-		}
-		else if (current>=65 && current<= 90)
-		{
-			int numAlphabet = message.charAt(i);
-			if(numAlphabet - shift < 65)
-			{
-				int j = numAlphabet - 65;
-				char nextKey = (char)(90 - (shift - j - 1));
-				decoded += nextKey;
-
-			}
-			else
-			{
-				char nextKey = (char)(current - shift);
-				decoded += nextKey;
-			}
-		}
-		else if (current>=97 && current <= 122)
-		{
-			int numAlphabet = message.charAt(i);
-			if(numAlphabet - shift < 97)
-			{
-				int j = numAlphabet - 97;
-				char nextKey = (char)(122 - (shift - j - 1));
-				decoded += nextKey;
-			}
-			else
-			{
-				char nextKey = (char)(current - shift);
-				decoded += nextKey;
-			}
-		}
-	}
-	return decoded;
-}
-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);
-	if(choice == 'E' || choice=='e')
-		System.out.println("ENCODED MESSAGE IS \n" + encode(message,shift)); //send our function to handle
-	if(choice =='D' || choice =='d')
-		System.out.println("DECODED MESSAGE IS \n" + decode(message,shift));
-}
 
-}
+    /**
+     * Encrypt text by shifting every Latin char by add number shift for ASCII
+     * Example : A + 1 -> B
+     *
+     * @param message
+     * @param shift
+     * @return Encrypted message
+     */
+    public static String encode(String message, int shift) {
+        String encoded = "";
+
+        while (shift >= 26) { // 26 = number of latin letters
+            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 += (char) (current > 'Z' ? current - 26 : current); // 26 = number of latin letters
+
+            } else if (IsSmallLatinLetter(current)) {
+
+                current += shift;
+                encoded += (char) (current > 'z' ? current - 26 : current); // 26 = number of latin letters
+
+            } else {
+                encoded += current;
+            }
+        }
+        return encoded;
+    }
+
+    /**
+     * Decrypt message by shifting back every Latin char to previous the ASCII
+     * Example : B - 1 -> A
+     *
+     * @param encryptedMessage
+     * @param shift
+     * @return message
+     */
+    public static String decode(String encryptedMessage, int shift) {
+        String decoded = "";
+
+        while (shift >= 26) { // 26 = number of latin letters
+            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 += (char) (current < 'A' ? current + 26 : current);// 26 = number of latin letters
+
+            } else if (IsSmallLatinLetter(current)) {
+
+                current -= shift;
+                decoded += (char) (current < 'a' ? current + 26 : current);// 26 = number of latin letters
+
+            } else {
+                decoded += current;
+            }
+        }
+        return decoded;
+    }
+
+    /**
+     *
+     * @param c
+     * @return true if character is capital Latin letter or false for others
+     */
+    private static boolean IsCapitalLatinLetter(char c) {
+        return c >= 'A' && c <= 'Z';
+    }
+
+    /**
+     *
+     * @param c
+     * @return true if character is small Latin letter or false for others
+     */
+    private static boolean IsSmallLatinLetter(char c) {
+        return c >= 'a' && c <= 'z';
+    }
+
+    /**
+     *
+     * @deprecated TODO remove main and make JUnit Testing
+     */
+    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));
+        }
+    }
+
+}