EXAM: e03: Final Exam

(15 pts) On handout C there is a class Dog with a main that creates some Dog objects.

Your job: figure out after which line of main() each of the following Dog objects is eligible for garbage collection.

If an object is still not eligible for garbage collection when the last line of main is reached, write “never”. Each answer should be a line number, or the word never.

(10 pts) Given the following program:

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import java.util.ArrayList;
public class BoxUnbox {
    public static void main(String [] args) {
	ArrayList<Integer> mylist = new ArrayList<Integer>();
	mylist.add(1);
	mylist.add(new Integer(4));
	Integer a = mylist.get(0) + mylist.get(1);
	int b = mylist.get(0);
	Integer c = a + b;
	Integer d = b;
	Integer e = mylist.get(mylist.get(0));
	System.out.println("a=" + a + " b= " + b + " c=" + c);
	System.out.println("d=" + d + " e= " + e);
    }
}

What is the output? Indicate by filling in the blanks:

a=____ b= ___ c=____
d=____ e= ____

For this question, you need page 1 of handout A with code for these files: Beverage.java, Edible.java, Food.java, FreeCandy.java and Product.java. These are classes used by a grocery store known as “Trader Bobs”.

Some of these methods will compile and run, while others will not.

Indicate, for each method, whether it compiles or not, and if it does compile, the output when invoked. in context of the classes on handout A and assuming the methods appear inside this class:

public class TraderBobs {
 // methods appear here
}

1. (3 pts)

     public static void TB01 () {
       Edible o = new Beverage(89,"Diet Coke",0,12.0);
       System.out.println("o: " + o.getFluidOunces());
     }
   

2. (3 pts)

     public static void TB02 () {
       Food r = new Food(99,"Almonds",100,0.63);
       System.out.println("r: " + r.getName());
     }
   

3. (3 pts)

     public static void TB03 () {
       Edible t = new FreeCandy(30);
       System.out.println("t: " + t.getPrice());
     }
   

4. (3 pts)

     public static void TB04 () {
       Product u = new Product(299,"Ziploc Bags");
       System.out.println("u: " + u.getName());
     }
   

(4 pts) For this question, and all the remaining ones on this exam, you should refer to page 1 of handout A which shows an excerpt of the javadoc for two classes.

Both solve the same problem in different ways. They both try to represent a set of set of numbers that someone might choose in a lottery drawing.

• LotteryPicks uses inheritance (is-a)
• LottoPicks uses composition (has-a)

Also refer to page 2 of handout B and handout C where you can find unit tests, and both sides of handout D where you can find the full source code, with a few lines left out.

It is those lines that you need to fill in on the remainder of this exam, starting with these lines from LotteryPick.

In all of these problems, if you are stuck, look through the unit tests, the javadoc, and the full listing for clues. Also, consider skipping the problem and coming back to it, after answering an easier one.

YOU MAY ONLY ADD CODE WHERE THERE ARE BLANKS.

YOU MAY NOT ADD ANY EXTRA CODE. ONLY ONE LINE OF CODE PER BLANK.

    public LotteryPick(LotteryPick other) {
	// use superclass constructor
	// in form ArrayList(Collection<? extends E> c) 


        _____________________________
    }

(4 pts) Fill in code for this method from LotteryPick.

DO NOT ADD CODE ANYWHERE EXCEPT IN THE BLANK.

ONLY ONE LINE OF CODE PER BLANK.

    public void sortNumbers() {
	// do it with one line of code,
	// taking advantage of the fact that
	// java.lang.Integer implements Comparable<Integer>


        ___________________________________
    }

(5 pts) Fill in code for this method from LotteryPick.

YOU MIGHT NOT NEED ALL THE BLANKS

DO NOT ADD CODE ANYWHERE EXCEPT IN THE BLANK.

ONLY ONE LINE OF CODE PER BLANK.

    public int numMatched(LotteryPick other) {
	if (!this.unique()) {
	    throw new IllegalArgumentException("this contains duplicates");
	}
	if (!other.unique()) {
	    throw new IllegalArgumentException("other contains duplicates");
	}

	// both now sorted; merge the two together, sort and count duplicates
	LotteryPick merged = new LotteryPick(this);
	merged.addAll(other);
	merged.sortNumbers();
	
        ____________________
	
	for (int i=1; i<merged.size(); i++) {
	    if (merged.get(i)==merged.get(i-1))
		dups ++;
	}

        ___________________
    }
}

(4 pts) NOTE: WE NOW TURN TO THE OTHER CLASS. We are no longer looking at LotteryPick, which uses inheritance.

We are looking at LottoPick, which uses Composition.

In all of these problems, if you are stuck, look through the unit tests, the javadoc, and the full listing for clues. Also, consider skipping the problem and coming back to it, after answering an easier one.

YOU MAY ONLY ADD CODE WHERE THERE ARE BLANKS.

YOU MAY NOT ADD ANY EXTRA CODE. ONLY ONE LINE OF CODE PER BLANK.

Fill in the blank in this constructor

    public LottoPick(LottoPick other) {
	// make sure to do a deep copy, not a shallow one
	// that is, don't make both LottoPicks refer to the same ArrayList
	// use one line of code


        _____________________________________________
    }

(4 pts) Fill in code for this method from LottoPick.

DO NOT ADD CODE ANYWHERE EXCEPT IN THE BLANK.

ONLY ONE LINE OF CODE PER BLANK.

    public void sortNumbers() {
	// do it with one line of code,
	// taking advantage of the fact that
	// java.lang.Integer implements Comparable<Integer>

       ___________________________________________
    }

(6 pts) Fill in code for this method from LottoPick.

YOU MIGHT NOT NEED ALL THE BLANKS

DO NOT ADD CODE ANYWHERE EXCEPT IN THE BLANK.

ONLY ONE LINE OF CODE PER BLANK.

BE CAREFUL: this is a static method, unlike it’s counterpart in LotteryPick.

    public static int numMatched(
    	   LottoPick first,
    	   LottoPick second) {
	if (!first.unique()) {
	    throw new IllegalArgumentException
	    	  ("this contains duplicates");
	}
	if (!second.unique()) {
	    throw new IllegalArgumentException
	    	  ("other contains duplicates");
	}

	// both now sorted; merge the two together, sort and count duplicates
	// HINT: LOOK AT THE IMPLEMENTATION in LotteryPick


	LottoPick merged = ______________


        _________________________________;

	merged.sortNumbers();


        __________________
	for (int i=1; i<merged.picks.size(); i++) {
	    if (merged.picks.get(i)==merged.picks.get(i-1))
		dups ++;
	}


        ____________________
    }