diff --git a/Test/Aufgabe2_KellerautomatTest.java b/Test/Aufgabe2_KellerautomatTest.java
index b3dedea..d4a393c 100644
--- a/Test/Aufgabe2_KellerautomatTest.java
+++ b/Test/Aufgabe2_KellerautomatTest.java
@@ -12,5 +12,6 @@ class Aufgabe2_KellerautomatTest {
         assertThrows(IllegalArgumentException.class,()->Aufgabe2_Kellerautomat.calculate("34+34+"));
         assertThrows(IllegalArgumentException.class,()->Aufgabe2_Kellerautomat.calculate("34+*"));
         assertThrows(IllegalArgumentException.class,()->Aufgabe2_Kellerautomat.calculate("8+9+7*2*"));
+        assertThrows(IllegalArgumentException.class,()->Aufgabe2_Kellerautomat.calculate("57-"));
     }
 }
\ No newline at end of file
diff --git a/doc/uebung_2 Schenk, Brandenberger, Fassbind.pdf b/doc/uebung_2 Schenk, Brandenberger, Fassbind.pdf
deleted file mode 100644
index 0c3f969..0000000
Binary files a/doc/uebung_2 Schenk, Brandenberger, Fassbind.pdf and /dev/null differ
diff --git a/src/Aufgabe2_Kellerautomat.java b/src/Aufgabe2_Kellerautomat.java
index 4807cc1..314d372 100644
--- a/src/Aufgabe2_Kellerautomat.java
+++ b/src/Aufgabe2_Kellerautomat.java
@@ -4,8 +4,16 @@ import java.util.Collections;
 import java.util.List;
 
 public class Aufgabe2_Kellerautomat {
-    private static String[] words = {"34+62+89+43+***", "31+78+987+1214++7++++++", "34+34+", "34+*", "8+9+7*2*"};
 
+    /**
+     * List of Words which will be calculated by Main Method
+     */
+    private static String[] words = {"34+62+89+43+***", "31+78+987+1214++7++++++", "34+34+", "34+*", "8+9+7*2*", "57-"};
+
+    /**
+     * Calculates all words in Array words
+     * @param args no args needed
+     */
     public static void main(String[] args) {
         for (String word : words) {
             try {
@@ -16,6 +24,12 @@ public class Aufgabe2_Kellerautomat {
         }
     }
 
+    /**
+     * Calculates the given Word
+     * @param word the word to calculate
+     * @return returns the result of the calculation
+     * @throws IllegalArgumentException if the word is invalid and can not be caluclated (not accepted words)
+     */
     public static int calculate(String word) throws IllegalArgumentException {
         List<Character> wordChars = new ArrayList<>();
         for (char symbol : word.toCharArray()) {
@@ -122,25 +136,47 @@ public class Aufgabe2_Kellerautomat {
         return -1;
     }
 
-    private static void dontAccept(String word) {
+    /**
+     * Called if word is invalid, throws exception with errormessage
+     * @param word the invalid word
+     */
+    private static void dontAccept(String word) throws IllegalArgumentException{
         throw new IllegalArgumentException("Word: " + word  + "\nnot accepted");
     }
 
+    /**
+     * Called if end state is reached, prints the accepted word and result (word is accepted)
+     * @param word the accepted word
+     * @param result the result
+     */
     private static void accept(String word, int result) {
         System.out.println("Word: " + word  + "\naccepted\nResult " + result);
     }
 
+    /**
+     * checks if a character is a operator
+     * @param symbol character to check
+     * @return true if character is a operator, false if not
+     */
     private static boolean isOperator(char symbol){
         return symbol == '+' || symbol == '*';
     }
 
-    private static int doOperation(char operator, int firstNumber, int secondNumber){
+    /**
+     * Calculates the result of a operation
+     * @param operator the operator
+     * @param firstNumber the first number of caluclation
+     * @param secondNumber the second number of calculation
+     * @return the result of the operation
+     * @throws IllegalArgumentException if the operator is invalid and can not be caluclated
+     */
+    private static int doOperation(char operator, int firstNumber, int secondNumber) {
         if(operator == '+'){
             return firstNumber + secondNumber;
         } else if(operator == '*'){
             return firstNumber * secondNumber;
         }
-        return -1;
+        throw new IllegalArgumentException("Invalid Operator: " + operator + "\n");
     }
 
 }