Add AtbashCipher.java

Author: Krounosity

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

@@ -0,0 +1,69 @@
+/*
+* The Atbash cipher is a simple substitution cipher that replaces each letter
+* in the alphabet with its reverse.
+* For example, 'A' becomes 'Z', 'B' becomes 'Y', and so on. It works
+* identically for both uppercase and lowercase letters.
+* It's a symmetric cipher, meaning applying it twice returns the original text.
+* Hence, the encrypting and the decrypting functions are identical
+* 
+* @author https://github.com/Krounosity
+* Learn more: https://en.wikipedia.org/wiki/Atbash
+*/
+
+package com.thealgorithms.ciphers;
+
+public class AtbashCipher {
+
+    private String toConvert;
+
+    // Default constructor.
+    AtbashCipher() {
+    }
+
+    // String setting constructor.
+    AtbashCipher(String str) {
+        toConvert = str;
+    }
+
+    // String getter method.
+    public String getString() {
+        return toConvert;
+    }
+
+    // String setter method.
+    public void setString(String str) {
+        toConvert = str;
+    }
+
+    // Checking whether the current character is capital.
+    private boolean isCapital(char ch) {
+        return ch >= 'A' && ch <= 'Z';
+    }
+
+    // Checking whether the current character is smallcased.
+    private boolean isSmall(char ch) {
+        return ch >= 'a' && ch <= 'z';
+    }
+
+    // Converting text to atbash cipher code or vice versa.
+    public String convert() {
+
+        // Using StringBuilder to store new string.
+        StringBuilder convertedString = new StringBuilder();
+
+        // Iterating for each character.
+        for (char ch : toConvert.toCharArray()) {
+
+            // If the character is smallcased.
+            if (isSmall(ch))
+                convertedString.append((char) ('z' - (ch - 'a')));
+            // If the character is capital cased.
+            else if (isCapital(ch))
+                convertedString.append((char) ('Z' - (ch - 'A')));
+            // Non-alphabetical character.
+            else
+                convertedString.append(ch);
+        }
+        return convertedString.toString();
+    }
+}