ITI 1121. Introduction to Computer Science II Laboratory 2


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Part I
Prerequisite material
Manipulating arrays and references
Understanding when to use “==” or “equals”
1 FindAndReplace
Complete the implementation of the (static) class method String[] findAndReplace(String[] in, String[]
what, String[] with) of the class Utils ( The method returns a copy of the array in where each
word occurring in the array what has been replaced by the word occurring at the corresponding position in
the array with. The array designated by in must remain unchanged.
Later in the semester, we will learn about exceptions. Exceptions provide tools for handling error
situations. In the meantime, the method findAndReplace returns null whenever the preconditions of the
methods are violated. In particular, the formal parameters cannot be null. For all three arrays, none of the
elements can be null. The query and replacement arrays must be of the same length.
Part II
Unit testing: JUnit
Introduction to unit testing
Although “testing shows the presence, not the absence of bugs”1 , testing is never the less an important
activity of software development. JUnit is a Java framework to assist you with this important task.
Your teaching assistant will now present a brief introduction and tour of JUnit. She/he will lead a
discussion around each test case found in what is the test case testing, what are
the strengths and weaknesses of the test set, what cases are missing, etc.
ITI 1121. Introduction to Computer Science II 2015-05-19, 11:30 Page 2 of 4
Ah, you are back! Make all the necessary changes to your method findAndReplace so that it passes all
the tests.
Part III
More objects
Further understanding of object-oriented programming
Problem solving using Java
2 Rational
Implement a class to represent rational numbers. Each rational number consists of a numerator and a
denominator, both of type int. Since each rational number has its own numerator and denominator, these
must be instance variables. Furthermore, good object-oriented programming suggests that the visibility of the
variables should be private.
3 Constructors
The class Rational has two constructors. One of them has two formal parameters, which provide the initial
values for both instance variables. The other constructor has a single parameter, which provides the initial
value for the numerator; the denominator is assumed to be 1.
4 getters
Implement access methods that return the numerator and denominator of this rational, but no setter methods.
An object that has no setter methods, and no other methods for transforming the state of the object, is said to
be immutable. Immutable is a great property. Do you see why? Discuss this with your neighbors and TA.
5 plus
Implement the instance method plus. The method has a single formal parameter, of type Rational. The
method returns a new Rational number that is the sum of this number and that of the parameter.
6 plus
Implement a class method plus. The method has two formal parameters, both of type Rational. The method
returns a new Rational number that is the sum of the two numbers.
ITI 1121. Introduction to Computer Science II 2015-05-19, 11:30 Page 3 of 4
7 gcd
Implement a private class method for calculating the greatest common divisor of two integers, which are the
formal parameters of the method.
8 reduce
Implement a private instance method called reduce that transforms this number into its reduced form.
9 reduce
Make all the necessary changes so that a rational number is always stored in reduced form.
10 equals
Implement the instance method public boolean equals(Rational o) that returns true if this fraction and the
one designated by o represent the same fraction (content equality).
11 toString
Add a method public String toString() that returns a String representation of this fraction with the
numerator followed by the symbol “/”, followed by the denominator. If the denominator is 1 then the method
returns a String consisting of the numerator only.
12 compareTo
Implements the instance method int compareTo( Rational o ). It compares this object with the specified
object for order. Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or
greater than the specified object.
Part IV
Documentation: JavaDoc
Introduction to JavaDoc
Another important aspect of software development is the documentation. JavaDoc is a format for your Java
comments, and a set of tools for producing Web pages automatically. In ITI1121, we are asking you to
document your code (variables, methods, etc.) using JavaDoc. Your teaching assistant will now present a
brief introduction of JavaDoc.
You must add JavaDoc comments for the class Rational.
ITI 1121. Introduction to Computer Science II 2015-05-19, 11:30 Page 4 of 4
1. Add JavaDoc comments for all the methods. Each comment should include a brief description of what
the method does and descriptions of the parameters and the return value using JavaDoc format.
2. Add a brief description of the class Rational, using the JavaDoc syntax, make sure to include the name
of the author of the class (you).
You can now produce HTML files automatically, either using your favorite IDE (DrJava, Eclipse, Netbeans,
etc.) or by running the javadoc command in a shell, the parameters are -d doc, followed by the name(s) of the
Java file(s) to be processed
> javadoc -d doc
When several files need to be processed simultaneously, use * in place of the names of the files.
> javadoc -d doc *
Part V
Quiz (1 mark)
Referring to the class Counter below, the keyword this can be omitted without affecting the
compilation or execution of the program.
True or False
public class Counter {
private int value = 0;
public Counter( int initialValue ) {
this.value = initialValue;
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