Add instruction to use Main class in ug, improve user feedback

docs/UserGuide.adoc

@@ -198,6 +198,8 @@ The help page is where you can get a quick summary of all of the features and co
 
 [[BeforeStart]]
 == Before you start
+. The programe evaluator searches for a class with the class name `Main` as the entry point into your program. Please ensure
+that you declare your *main method* in a class called `Main`.
 
 . The program evaluator uses *stdin* to feed your program inputs and *stdout* to receive your program's outputs. Thus,
 it is important that your program uses the `Scanner` class to read inputs and for you to print your results.

docs/diagrams/NoteSavingSequence.puml

@@ -10,4 +10,4 @@ NotesLogicManager -> UI: getNoteAndSketchPair()
 UI -> NotesLogicManager: Note and Sketch
 NotesLogicManager -> NoteBankStorage: Modify and Save  new note
 NotesLogicManager -> Sketch: saveSketch(sketchId, sketch)
-@enduml
+@enduml

src/main/java/com/dukeacademy/logic/commands/submit/SubmitCommand.java

@@ -70,7 +70,7 @@ public CommandResult execute() throws CommandException {
             resultsOptional = this.programSubmissionLogic.submitUserProgram(userProgram);
         } catch (IncorrectCanonicalNameException e) {
             logger.warning("Main class not detected, command will not be executed");
-            throw new CommandException("Main class needed as entry point.");
+            throw new CommandException("Please write your main method in a class called Main");
         } catch (EmptyUserProgramException e) {
             logger.warning("Program is empty, command will not be executed");
             throw new CommandException("Program must not be empty.");

src/main/java/com/dukeacademy/testexecutor/TestExecutorUtils.java

@@ -60,14 +60,20 @@ private static boolean checkContainsMatchingClass(String canonicalName, String p
         String[] canonicalNameSplit = canonicalName.split("\\.");
         String className = canonicalNameSplit[canonicalNameSplit.length - 1];
 
+        // Remove any class declarations that could be in comments
         String programRemoveComments = program
                 .replaceAll("(?:/\\*(?:[^*]|(?:\\*+[^*/]))*\\*+/)|(?://.*)", "");
+
+        // Split the program by class declaration with the required class name
         String[] programSplit = programRemoveComments.split("class " + className);
 
         if (programSplit.length == 1) {
+            // Class declaration not found
             return false;
         }
 
+        // For each occurrence of the class declaration, check to see if it is an outermost class declaration by
+        // matching the number of opening/closing braces
         for (int i = 1; i < programSplit.length; i++) {
             Stack<Character> braceStack = new Stack<>();
 

src/test/java/com/dukeacademy/logic/commands/submit/SubmitCommandTest.java

@@ -55,7 +55,8 @@ class SubmitCommandTest {
         // Check that an exception is thrown if no appropriate class name is found
         UserProgram invalidClassNameSubmission = new UserProgram("Main", "public class Test {}");
         submissionLogic.setUserProgramSubmissionChannel(() -> invalidClassNameSubmission);
-        assertThrows(CommandException.class, "Main class needed as entry point.", command::execute);
+        assertThrows(CommandException.class, "Please write your main method in a class called Main",
+                command::execute);
 
         // Check that questionsLogic has changed accordingly
         List<Question> expected = TypicalQuestions.getTypicalQuestions();