Assignment 2 Solution

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This assignment should help you gain practice with creating and editing basic Java classes based on given speci cations.


Do the following exercises, each in a di erent le. Your lenames should be

Each le should have a comment including your name at the top of the le. Each le should also have appropriate comments throughout the program. When adding to a pre-supplied le, clearly indicate, using comments, which parts are your additions.

Integer Set


Create class IntegerSet in its own le

An IntegerSet object holds integers in the range 0-100

This is represented by an array of booleans. Array element i is set to true if the integer i is in the set and false otherwise.

Create these methods for the class (these should be the only public meth-ods)


public IntegerSet union(IntegerSet iSet)

public IntegerSet intersection(IntegerSet iSet) public IntegerSet insertElement(int data) public IntegerSet deleteElement(int data) public boolean isEqualTo(IntegerSet iSet) public String toString()

The constructor (no arguments) initializes the array to represent the “empty set” (no integers in the set)


Method union creates and returns a new set that is the set-theoretic union of the two existing sets (the calling object and the parameter). An element is in the union if it is in either of the two starting sets

Method intersection creates and returns a new set that is the set-theoretic intersection for he two existing sets. An element is in the inter-section if it’s in both of the starting sets.

Method insertElement adds the argument(an integer) to the set (the calling object) and should also return that set (this allows calls to be cascaded)

Method deleteElement removes the argument from the set and should also return the set, to allow cascading

Method isEqualTo returns true if the two sets are equal (if they have all the same elements) and false otherwise

Method toString returns a string containing the set elements as a list of numbers in ascending order, separated by spaces. Include only the elements present in the set. Use \—” to represent an empty set

Fraction class


Begin with this Fraction class, as discussed in the lecture and add the fol-lowing features:

You will create methods with the following signatures: public Fraction simplify()

public Fraction add(Fraction f) public Fraction subtract(Fraction f) public Fraction multiply(Fraction f) public Fraction divide(Fraction f)

The simplify method will return a simpli ed version of the calling ob-ject. This method should return a new Fraction (simpli ed), but not change the original one. The fractions in the form N0 should have a sim-pli ed form of 01 . Any other fraction has the usual mathematical de nition of “simpli ed form”. This will require nding the GCD of the numerator and denominator. One useful algorithm for doing so is

Euclid’s algorithm/the Euclidean algorithm.

Methods add, subtract, multiply, divide should take in a Fraction as a parameter and perform the given computation between the calling


object and the parameter object (The calling object is always the rst operand). The result of each operation should always be a fraction re-turned in simpli ed form. Example calls: f1.add(f2) means to return the value f1 + f2, f1.divide(f2) means to return the value f1=f2.

In divide, if an attempt is made to divide by a fraction with the numer-ator 0, default the result to 01 . This division is actually unde ned, but we need to return something from the method and this is a \sane” value

Be sure that your new methods enforce the same rules on the data as the original methods do { the denominator must always be non-negative (negative fractions have the negative sign in the numerator) and the de-nominator must never be zero


I’ve provided a le to help you get started with testing. This is not a com-prehensive set of tests (so make sure you do some of your own), but will get you started. Also, you will need to include the HW2Tester class (unchanged) in your jar le when you submit, as indicated at the end of this.

Here is the le which contains some tests for both the IntegerSet and Fraction classes.

Sample Run of HW2Tester

After set1.insertElement(10), set1 = 0 2 8 10 default IntegerSet is = — set1 = 0 2 4 6 8 10 12 95 100

set2 = 0 3 6 9 12

set1.union(set2) = 0 2 3 4 6 8 9 10 12 95 100 set1.intersection(set2) = 0 6 12 set1.deleteElement(2) = 0 4 6 8 10 12 95 100 set1.isEqualTo(set1) = true set1.isEqualTo(set2) = false

Fraction tests:

4/6 simplified = 2/3

75/175 simplified = 3/7

-6/17 simplified = -6/17

f1 = 4/6

f2 = 75/175

f3 = -6/17

4/6 + 75/175 = 23/21


4/6 – 75/175 = 5/21

4/6 * 75/175 = 2/7

4/6 / 75/175 = 14/9

75/175 + -6/17 = 9/119

75/175 – -6/17 = 93/119

75/175 * -6/17 = -18/119

75/175 / -6/17 = -17/14

75/175 / 0/1 = 0/1


Pack all of your les (class les and source code) into a fully runnable JAR le called hw2.jar (this will be discussed in class, see the links on the class website for more details). The main program that the jar le should execute is the unchanged HW2Tester program downloaded above. I should be able to run the HW2Tester main() method from your jar le with the command:

java -jar hw2.jar

Submit your jar le via the Blackboard submission link for assignment 2.