Added exception handling for registerUser Method

src/main/java/org/example/Administration.java

@@ -185,8 +185,23 @@ public class Administration {
             }
             else if(findProfessorById(UserId) == null || findAdminById(UserId) == null || findStudentById(UserId) == null)
             {
-                System.out.println("The Id has not been used already!");
-                correctData = true;
+                String substring = UserId.substring(1);
+
+                if(!rightPrefix(UserId, userType))
+                {
+                    correctData = false;
+                }
+                else if(!isNumber(substring))
+                {
+                    System.out.println("Every character besides the first one need to be digits");
+                    correctData = false;
+
+                }
+                else{
+                    System.out.println("The Id has not been used already!");
+                    correctData = true;
+                }
+
             }
 
             switch (userType)