COMP3200 Anonymous Questions and Answers

This page lists the various questions and answers. To submit a question, use the anonymous questions page. You may find the keyword index and/or top-level index useful for locating past questions and answers.

We have taken the liberty of making some minor typographical corrections to some of the questions as originally put. Although most of the questions here will have been submitted anonymously, this page also serves to answer some questions of general interest to those on the course.

Question 101:

Submission reference: IN2654

When finding and removing from a collection using while loop. please could you explain further what the line which follows the while condition means and why its needed and what the 2nd word is? i understand the first word is a data type because its starts with a capital letter. e.g from the lecture slides when removing:

Track t = it.next();

Track track = tracks.get(index);

Answer 101:

In both cases, a variable of type Track is being declared and initialised in a single statement. In the first example, the variable is called t and in the second it is called track.

In the first example, the variable is being initialised by calling the next() method on the Iterator object called it. In the second example, the variable is initialised with the Track object returned by a call to the get() method on a tracks ArrayList.

Question 100:

Submission reference: IN2653

For some reason my test class is not testing, so is this method right. Im not sure whether im searching for the right thing in the while loop

code deleted

Answer 100:

The test class should always successfully compile against your code unless you have changed any of the pre-defined method headers so it would be worth trying to fix that.

No, that is quite a long way from being correct. For instance, you aren't using the hasNext method of the Iterator to control the loop or check that there is another Assistant object to consider before calling the next method. Also, your logic is incorrect as it will never set the location or availability of the target assistant.

Keywords: assign2 , method-setAvailability

Question 99:

Submission reference: IN2652

for Question 97 (2022), would this be better as it stops the while loop searching for any more identities?

code deleted

Answer 99:

Unfortunately, what you have implemented doesn't work because it exits the loop if the first assistant in the collection doesn't have a matching identity.

However, that solution is also problematic because it hides the fact that the loop is not actually going to iterate over the collection, as appears to be the case from the loop's condition. In effect, a break statement is equivalent to a goto statement and it has long been considered a bad idea - Edsger Dijkstra wrote an influential rationale for this back in 1968. For a more recent explanation see Every wondered why goto is considered harmful.

It would be much clearer to express the loop's condition as a search as described in the Monday lecture in week 16. That way, it will be clear from the loop's condition that the iteration either stops when the matching assistant has been found or there are no more to check.

Keywords: assign2 , method-setAvailability , break-statement , goto-statement

Question 98:

Submission reference: IN2651

In assignment 2 its not been specified that we need to include error prevention f.e. if inputting an identity that's not in the ArrayList for the setAvailability method. currently my program just does nothing, do we need to be coding checks and error messages for invalid inputs like this?

Answer 98:

Good question. If the spec. doesn't explicitly say that you should print an error message then don't do so. If a matching Assistant cannot be found for a given identity, just do nothing.

Keywords: assign2 , error-messages , method-setAvailability

Question 97:

Submission reference: IN2650

Hello, i believe I've finished this method the correct way, would this achieve full marks?

code deleted

Answer 97:

The logic looks correct. However, there are a couple of improvements you could make in terms of quality:

• Given that identities are unique, once you have found a match, there is no need to examine any more for a match in the collection.
• Since a boolean variable can only be either true or false, if it isn't true it must be false, so there is no need to check for that value.

Keywords: assign2 , method-setAvailability

Referrers: Question 99 (2022)

Question 96:

Submission reference: IN2649

code deleted

Answer 96:

Unfortunately, your overall approach really needs a rethink as it will rarely find a matching assistant. The approach you appear to be trying is to start with a distance of 0 from the target location and then gradually increasing that distance until an available assistant is found. The problem is that that approach would only work if you iterate over the collection multiple times: firstly test everyone with a distance of 0, then of 1/-1, then of 2/-2, etc. However, as you only have one loop, the effect is that you try the different distances with different assistance on the only iteration.

While your approach would work, if you had enough multiple iterations, it's not really a viable way to tackle this method and there are much more efficient approaches that genuinely only require a single iteration.

One way to approach it is to choose the first available assistant but replace them if you find a closer one, and repeat that process until you have checked them all once.

Keywords: assign2 , method-findNearestAvailable

Question 95:

Submission reference: IN2648

I am attempting to finish the challenge question but I could not figure out the last two failures given to me by the test class. The two failures are AssistantCentreTest.findAssistantNeighbours() and AssistantCentreTest.findAssistantMultipleNeighbours()

code deleted

Answer 95:

The source of the problem is what you are doing in the final else-part inside the loop.

Question 94:

Submission reference: IN2647

code deleted

Answer 94:

This is a method in which you will definitely need to consider every Assistant object in the collection. So, a return statement inside the loop will be inappropriate. Therefore, the final statement of the method will be one that returns the Assistant object that was found during the iteration.

At the moment, the logic in the body of your method needs a complete rethink because you should not be altering the value of the location parameter.

Keywords: assign2 , method-findNearestAvailable

Question 93:

Submission reference: IN2646

Good morning, im trying to work through the availability part of this method and im not sure what method to call in the Assistant class as none that involve availability use parameters. This is what ive tried but it gives me an error that this method cannot be applied to given types.

assistant.isAvailable(available);

Answer 93:

In the Assistant class there are three methods related to availability: isAvailable, setAvailable and setOccupied. None take a parameter. That's because the Assistant object has all the information it needs internally to be able to carry out the associated action:

• isAvailable returns the current availability of the Assistant.
• setAvailable sets the availability to true.
• setOccupied sets the availability to false.

So, to complete the setAvailability method, you need to work out which of those need to be called depending on the value of the available parameter to the setAvailability method.

Keywords: assign2 , method-setAvailability

Referrers: Question 142 (2022)

Question 92:

Submission reference: IN2645

Hello, i am starting the setAvailablity method and wondering if it needs to be a for each or while loop?

Answer 92:

A good way to answer that for yourself is to see if you can work out whether you will always need to iterate over the whole collection (for-each loop) or might be able to stop before reaching the end (while-loop). For instance, if you might find the Assistant with matching identity in the first location of the collection then you could stop after the first one and not look at the rest. That would mean that a while-loop rather than a for-each loop would be appropriate.

Keywords: assign2 , method-setAvailablity

Question 91:

Submission reference: IN2644

taking in your feedback from Question 90 (2022), ive got this code, but it gives me the error: method getLocation in class Assistant cannot be applied to given types; required: no arguments found: int reason: actual and formal argument lists differ in length. im not sure what this means

code deleted

Answer 91:

The getLocation method in the Assistant class doesn't take a parameter - note in the source of that class that its parentheses are empty. However, note that if you want to change the location of an Assistant, getLocation is not the method to call. There is a different one - not called setLocation - that you will find if you look in the source of the Assistant class. That method does take a parameter.

Keywords: assign2 , method-setAvailability

Question 90:

Submission reference: IN2643

this is the if statement i have created for the set availability method for just the location bit, not the availability, and im not sure how to set the location to the value entered in the parameter. The setLocation(getLocation()); line gives me an error that getLocation is not a declared method.

code deleted

Answer 90:

Because you need to change the location of the matching individual Assistant object, you need to call the methods on that Assistant object. For instance, along these lines:

assistant.methodName(any-parameters-required);

Keywords: assign2 , method-setAvailability

Referrers: Question 91 (2022)

Question 89:

Submission reference: IN2642

I've written comments prepending some private methods I created for Assignment 2's AssistantCentre class. By default Javadoc doesn't create documentation for comments prepended to a private method. Are my comments necessary? If so, is it necessary to configure Javadoc to also create documentation files for my private methods?

Answer 89:

It is best to include them anyway. Javadoc can be configured to show the comments for private methods but it doesn't by default.

Keywords: assign2 , comment

Question 88:

Submission reference: IN2641

i have started my setAvailability method and not sure if ive started it correct. This is what ive gone with and at the moment have one error on the assistant.getLocation = location; line which says getLocation is undeclared.

code deleted

Answer 88:

Once you have found the matching Assistant object, you need to set its location and availability via method calls rather than assignments. If you look at the source code of the Assistant class you should be able to identify the methods your code needs to call.

Also, have a think about whether you need to continue the iteration once the Assistant has been identified.

Keywords: assign2 , method-setAvailability

Question 87:

Submission reference: IN2640

Would this void list method do what its meant to do?

code deleted

Answer 87:

That looks fine.

Keywords: assign2 , method-list

Question 86:

Submission reference: IN2638

For Question 85 (2022), thank you for your feedback. Would this method now be correct?

code deleted

Answer 86:

Yes, that is much better. Just remember that variable names should always start with a lower-case letter. Only class names should start with an upper-case letter.

Keywords: assign2 , method-getNumberOfAssistants

Question 85:

Submission reference: IN2637

Good afternoon, would it be possible to tell me what i am doing wrong here. I get loads of errors for this. I understand i need to be returning the count that i have attempted to create in this method but im just unsure on how to execute it.

code deleted

Answer 85:

You have a local variable assistants which you are trying to use as an integer variable, but you have given it the type Assistant. So you need to change the type. Also, I would advise against giving the local variable the same name as the collection field ecause that will be confusing and prevent you from accessing the field.

Another issue is the value you are returning at the end of the method. That should be the count of how many assistants were found at the given location but you are returning something related to the size of the collection, which is unrelated to the number found.

Keywords: assign2 , method-getNumberOfAssistants

Referrers: Question 86 (2022)

Question 84:

Submission reference: IN2636

In the brief for assignment 2 a style guide is referenced. The style guide advises to put curly brackets on the end of the line for anything other than methods or classes. e.g.

while(condition) {
     statements
}

while(condition)
{
     statements
}

Answer 84:

You are welcome to use your own style. The only requirement is that you are consistent in how you lay out your code. You won't lose marks if you use a different style.

Keywords: assign2 , style

Question 83:

Submission reference: IN2635

In regard to the last lesson, as you said we would need iterators and while loops for our assignment 2, in my case I have "finished" the assignment (no erros/failures from test class) however I used no iterators/while loops as I just used a combination of everything learned before project week (plus a bit extra learning for things like challenge question). Would this make me lose marks because of this or it is ok to leave my code unchanged?

Answer 83:

As long as your code is functionally correct, then you won't lose marks if you haven't explicitly used while-loops and Iterators. You should thoroughly test your code with data that goes beyond that in the test class to really gain confidence.

While it is possible to complete the assignment accurately without while and Iterator, you have to be really careful and the quality of your code might suffer as a result.

Keywords: assign2 , Iterator

Question 82:

Submission reference: IN2634

    public void listAllFiles(){
	for(String files:files){
	    System.out.println(files);
	}
    }

    public void listAllFiles(){
	for(String shaek:files){
	    System.out.println(files);
	}
    }

Answer 82:

The difference is that you are using the name files for two different things in the first example. In the first example, the local variable, which is the for-loop variable, is what gets used in the body of the loop. So, as it gets set, one after the other, to the filenames in the collection, each different name gets printed out.

In the second version, you are not using the loop variable in the body of the loop, so each time around the loop, your code is printing out the full list.

A better approach is to use different names for the loop variable and the collection and use the local variable name in the body of the loop. For instance

    public void listAllFiles() {
	for(String filename : files){
	    System.out.println(filename);
	}
    }

Keywords: method-listAllFiles