EECS2030E Test 3

Version C

You have 80 minutes to complete this test. This is a closed book test.

GETTING STARTED

  1. Start eclipse.
  2. Download this project file.
  3. Import the test project by doing the following:
    1. Under the File menu choose Import...
    2. Under General choose Existing Projects into Workspace and press Next
    3. Click the Select archive file radio button, and click the Browse... button.
    4. Navigate to your home directory (the file chooser is probably in the workspace directory).
    5. Select the file test3C.zip and click OK
    6. Click Finish.
  4. All of the files you need for this test should now appear in eclipse.
  5. Open a terminal. You will use this terminal to submit your work.
  6. Copy and paste the command cd workspace/Test3C/src/test3 into the terminal and press enter.

Resources

Question 1 (18 marks total)

IMPORTANT NOTE: You are not given the fields needed to implement the class in this question. You must analyze the API of the class, decide what fields are required, and add the fields to the class.

Implement the class described by this API. You do not have to include javadoc comments.

submit 2030L secEtest3C PiggyBank.java

SOLUTION using a list
SOLUTION using a map

Question 2 (12 marks total)

A. (6 marks)

Consider the following list: 

List<String> t = new ArrayList<>();
/* some code not shown that adds many strings to t */

(a): Show how to make a shallow copy of the list t using Java. 

List<String> copy = new ArrayList<>(t);

// OR 

List<String> copy = new ArrayList<>();
for (String s : t) {
  copy.add(s);
}

(b): Show how to make a deep copy of the list t using Java. 

List<String> copy = new ArrayList<>();
for (String s : t) {
  copy.add(new String(s));
}

(c): Does the method showCoins from the programming question have to return a deep copy? Explain your answer.

No, a deep copy is not required because the elements of the collection are Coins and Coins are immutable.


B. (3 marks)

When a class has fields that are not of primitive type, we often need to consider using composition instead of aggregation.

(a) What is the main disadvantage of using composition instead of aggregation?

The main disadvantage is the cost of time and memory in making defensive copies of the field.

(b) Under what circumstances is composition required? Your answer should be more detailed than "composition implies ownership".

Composition is required when there are class invariants that depend on the state of non-primitive fields.


C. (3 marks)

Examine the Coin API. Which field, constructor, or method could be removed that would cause the least amount of inconvenience for clients of the class? Explain your answer. (Hint: The correct answer is not toString).

The constructor can be removed (made private) because clients don't need to create new Coin objects. References to all of the possible Coin objects are available as public static final fields (Coin.PENNY, Coin.NICKEL, etc), and coins are immutable so references to Coin objects can be shared freely without worrying that the value of the coin might change.

All of the other public methods are very useful: compareTo is useful for sorting collections of coins, equals is useful (if there is a public constructor) for comparing coins for equality, hashCode is required if equals is overridden, getValue is useful for getting the numeric value of a coin, and toString is useful for printing coins.

If the constructor is removed (made private), then both equals and hashCode can be safely removed; why?


submit 2030L secEtest3C answers.txt