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csis10a-lab-11

Part A - Creating a Classes

Prerequisite: Lecture or Reading on Chapter 11

Clone or download csis10a-lab-11.

Exercise 1

The point of this exercise is to practice the mechanical part of creating a new class definition and code that tests it.

In the board game Scrabble, each tile contains a letter, which is used to spell words, and a score, which is used to determine the value of words. Refer to the Time class as a model for this exercise, or bring up sections 11.2 – 11.6 of your text.

  1. A starting Tile class that represents Scrabble tiles has been provided for you. Start by declaring the instance variables for class Tile. The instance variables should be a character named letter and an integer named value.
  2. Write a no-arg constructor that initializes a Tile to the letter ‘A’ with a value of 1.
  3. Write a constructor that takes parameters named letter and value and initializes the instance variables.
  4. Write a method named printTile that takes a Tile object as a parameter and prints the instance variables in a reader-friendly format.
  5. Verify your new class works by running main and observing the output.
  6. Finally,add code in main to creates a Tile object with the letter Z and the value 10, and then use printTile to print the state of (all the information in side) the object.

Exercise 2

Now create a new class called Date. Write the class definition for Date, as an object type that contains three integers, year, month and day. This class should provide two constructors. The first should take no parameters. The second should take parameters named year, month and day, and use them to initialize the instance variables.

Finally, write a main method that creates a new Date object named birthday. The new object should contain your birthdate. You can use either constructor.

Part B - Introduction to Unit Testing

What is a unit test?

In computer programming, unit testing is a method by which individual units of source code, sets of one or more computer program modules together with associated control data, usage procedures, and operating procedures are tested to determine if they are fit for use. [1]

Unit Testing Frameworks

Java has a number of excellent unit test frameworks to use. For this lab, we will be using JUnit which is probably the most commonly used one.

In order to simplify the execution of unit tests, we will create our unit tests in a Maven project. If you follow a few conventions Maven will execute your unit tests for you on request or with every build.

Your Tasks

Create a project using Maven

  1. Create a new Maven project named unittest with the command below. When prompted, the groupId should be csis10a, the artifactId should be unittest.:
cd ~/csis10a
mvn archetype:generate
  1. You should now have a directory named ~/csis10a/unittest. Open this project using IntelliJ or Visual Studio Code

MathUtil

MathUtil will illustrate using static methods like functions.

  1. Create the class csis10a.MathUtil. To do this in your editor, expand the src directory in your editor's sidebar until you see the csis10a package. Right-click on csis10a and select new Java class and name it MathUtil.
  2. Create 2 static methods in MathUtil and implement them:
  • add which will add 2 double values together and returns the result
  • subtract which will subtract 2 double values and returns the result.

Now you will create a corresponding unit test named MathUtilTest. It is a convention (but not a rule) that a unit test is the name of the class being tested with Test appended to the end. A Test is just a regular old class but used in a specific way.

  1. Create the test csis10a.MathUtilTest. To do this, expand the test directory in your editor's sidebar until you see the csis10a package. Right click on csis1a and select new Java Test and name it MathUtilTest
  2. Create 2 method stubs in MathUtilTest. Don't worry about the implementation yet:
  • public void addTest(). Inside this method you will test the add method of MathUtil.
  • public void subtractTest(). Inside this method will test the subtract method of MathUtil.
  1. Add the following import: import org.junit.Assert. Here's the javadoc for Assert. Asserts are the bread-and-butter of unit testing and control whether a test passes or fails. Here's some example assertions:
Assert.assertEquals("foo", "bar"); // Fails

double a = 1;
double b = 2;
double epsilon = 0.00000000001; // Remember don't uses == with floating point numbers
Assert.assertEquals(a, b, epsilon); // Fails
Assert.assertTrue(a < b);           // Passes

Time t = new Time(1, 2, 3);
Time u = t
Assert.assertNotNull(t);            // Passes
Assert.assertSame(t, t);            // Passes
  1. Import org.junit.Test and add the @Test annotation to your testing methods:
@Test
public void addTest() { ... }
  1. Implement your tests

BetterTime

  1. Copy the file BetterTime.java into your maven project at src/main/java/csisi10a You'll need to make sure that the first line in BetterTime is the package name: package csis10a;.
  2. Following a similar procedure as above, create a unit test for BetterTime and implemen some tests to verify it's methods.