Change public classes/methods to package-private

exercises/atbash-cipher/.meta/src/reference/java/Atbash.java

 import java.util.ArrayList;
 import java.util.List;
 
-public class Atbash {
+class Atbash {
 
     private static final int GROUP_SIZE = 5;
     private static final String PLAIN = "abcdefghijklmnopqrstuvwxyz";
     private static final String CIPHER = "zyxwvutsrqponmlkjihgfedcba";
 
-    public String encode(String input) {
+    String encode(String input) {
         String encoded = stripInvalidCharacters(input).toLowerCase();
         String cyphered = "";
 
         return splitIntoFiveLetterWords(cyphered);
     }
 
-    public String decode(String input) {
+    String decode(String input) {
         String encoded = stripInvalidCharacters(input).toLowerCase();
         String deciphered = "";
 
         return deciphered;
     }
 
-    private String stripInvalidCharacters(String input) {
+    String stripInvalidCharacters(String input) {
         String filteredValue = "";
 
         for (char c : input.toCharArray()) {