not working correctly

Crypto/src/main/java/ROT13.java

@@ -1,3 +1,7 @@
+import javax.security.sasl.SaslServer;
+import java.io.*;
+import java.nio.file.Files;
+
 import static java.lang.Character.isLowerCase;
 import static java.lang.Character.isUpperCase;
 import static java.lang.Character.toLowerCase;
@@ -11,7 +15,7 @@ public class ROT13  {
 
     ROT13(Character cs, Character cf) {
         rotateBy = numbersByCount(cs, cf);
-        rotatedAlphbet = rotate("abcdefghijklmnopqrstuvwxyz", cf).toCharArray();
+        rotatedAlphbet = rotate("abcdefghijklmnopqrstuvwxyz").toCharArray();
     }
 
     ROT13() {}
@@ -37,7 +41,9 @@ public class ROT13  {
     }
 
     public static void main(String[] args){
-        new ROT13('a','n');
+        ROT13 rot13 = new ROT13('a','n');
+        rot13.encryptFile("sonnet18.txt");
+        rot13.decryptFile("sonnet18.enc");
         //System.out.println(new ROT13().crypt("Gb trg gb gur bgure fvqr!"));
     }
 
@@ -55,7 +61,6 @@ public class ROT13  {
             } else{
                 sb.append(car);
             }
-
         }
         return sb.toString();
 
@@ -78,7 +83,40 @@ public class ROT13  {
 
     public String decrypt(String text) {
 
-        return this.crypt(text);
+        char[] cars = text.toCharArray();
+
+        StringBuilder sb =  new StringBuilder();
+
+        for(int i = 0; i < cars.length; i++){
+            if(Character.isLetter(cars[i])){
+                sb.append(cars[i]);
+                if(rotateBy - i < 0){
+                    System.out.println(rotateBy -1);
+                    sb.append(rotatedAlphbet[(rotateBy - i) + (rotatedAlphbet.length -1)]);
+                } else {
+                    sb.append(rotatedAlphbet[rotateBy - i]);
+                }
+            } else {
+                sb.append(cars[i]);
+            }
+        }
+        return sb.toString();
+    }
+
+    public String rotate(String s) {
+        char[] cars = s.toCharArray();
+
+        int looper = rotateBy;
+        char temp;
+        while(looper != 0){
+            temp = cars[0];
+            for(int i = 0; i < cars.length -1; i++){
+                cars[i] = cars[i +1];
+            }
+            cars[cars.length -1] = temp;
+            looper--;
+        }
+        return new String(cars);
     }
 
     public static String rotate(String s, Character c) {
@@ -96,6 +134,66 @@ public class ROT13  {
         return new String(cars);
     }
 
+    public void encryptFile(String fileName){
+        try{
+            BufferedReader br = new BufferedReader(new FileReader(fileName));
+            StringBuilder sb = new StringBuilder();
+            String line = br.readLine();
+
+            while(line != null){
+                sb.append(line);
+                sb.append("\n");
+                line = br.readLine();
+            }
+
+            String encryptedFile = this.crypt(sb.toString());
+
+            try {
+                File file = new File("sonnet18.enc");
+                FileWriter fileWriter = new FileWriter(file);
+                fileWriter.write(encryptedFile);
+                fileWriter.flush();
+                fileWriter.close();
+            } catch (IOException e) {
+                e.printStackTrace();
+            }
+
+            System.out.println(encryptedFile);
+
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    public void decryptFile(String fileName){
+        try{
+            BufferedReader br = new BufferedReader(new FileReader(fileName));
+            StringBuilder sb = new StringBuilder();
+            String line = br.readLine();
+
+            while(line != null){
+                sb.append(line);
+                sb.append("\n");
+                line = br.readLine();
+            }
+
+            String decryptFile = this.decrypt(sb.toString());
 
+            try {
+                File file = new File("sonnet18dec.txt");
+                FileWriter fileWriter = new FileWriter(file);
+                fileWriter.write(decryptFile);
+                fileWriter.flush();
+                fileWriter.close();
+            } catch (IOException e) {
+                e.printStackTrace();
+            }
+
+            System.out.println(decryptFile);
+
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
 
 }

sonnet18.enc

@@ -0,0 +1,14 @@
+Funyy V pbzcner gurr gb n fhzzre’f qnl?
+Gubh neg zber ybiryl naq zber grzcrengr:
+Ebhtu jvaqf qb funxr gur qneyvat ohqf bs Znl,
+Naq fhzzre’f yrnfr ungu nyy gbb fubeg n qngr;
+Fbzrgvzr gbb ubg gur rlr bs urnira fuvarf,
+Naq bsgra vf uvf tbyq pbzcyrkvba qvzz'q;
+Naq rirel snve sebz snve fbzrgvzr qrpyvarf,
+Ol punapr be angher’f punatvat pbhefr hagevzz'q;
+Ohg gul rgreany fhzzre funyy abg snqr,
+Abe ybfr cbffrffvba bs gung snve gubh bj’fg;
+Abe funyy qrngu oent gubh jnaqre’fg va uvf funqr,
+Jura va rgreany yvarf gb gvzr gubh tebj’fg:
+   Fb ybat nf zra pna oerngur be rlrf pna frr,
+   Fb ybat yvirf guvf, naq guvf tvirf yvsr gb gurr.

sonnet18dec.txt

@@ -0,0 +1 @@
+enczb  yynuF