©2006 Felleisen, Proulx, et. al.

8  Designing Tests for State Change Abstracting with Function Objects

Goals

In the first part of this lab you will learn how to correctly design tests for the methods that change the state of an object.

In the second part of the lab you will learn to abstract over the functional behavior.

8.1  Designing Tests for State Change

For this part download the files in Lab8Part1.zip. The folder contains the files ImageFile.java and Examples.java.

Starting with partially defined classes and examples will give you the opportunity to focus on the new material and eliminate typing in what you already know. However, make sure you understand how the class is defined, what does the data represent, and how the examples were constructed.

Create a new Project Lab8Part1 and import into it the files ImageFile.java and Examples.java. Also import the TestHarness.jar files and jpt.jar from the previous lab.

• Design the method crop that changes the dimensions of an ImageFile object to the given width and height. The Examples class contains comments on what needs to be done to design the tests. Follow the outline given by the comments to design the needed tests.

• Design the method changeName that allows us to change the name field of an ImageFile object. Design the tests.

8.2  Abstracting with Function Objects

For this part download the files in Lab8Part2.zip. The folder contains the files ISelect.java, LoIF.java, MtIF.java, ConsLoIF.java, and Examples.java.

Create a new Project Lab8Part1 and import into it the file ImageFile.java from the Part 1 and the files \ISelect.java, LoIF.java, MtIF.java, ConsLoIF.java, and Examples.java from the Lab8Part2 folder. Again, import the test harness files and jpt.jar from the previous lab.

1. Design the method smallerThan40000 in the class ImageFile that determines whether the file size is smaller that 40000 pixels. The size is computed as a product of the image file's width and height.

2. Design the method allSmallerThan40000 that determines whether all items in a list are smaller that 40000 pixels. The size is computed as a product of the image file's width and height.

3. Design the method nameShorterThan4 that determines whether the name in this ImageFile object is shorter than 4.

4. Design the method allNamesShorterThan4 that determines whether all items in a list have a name that is shorter than 4 characters.

5. Design the class SmallerThan40000 that implements the ISelect interface with a method that determines whether the size of the given ImageFile is less than 40000.

   Make sure in the class Examples you define an instance of this class and test the method.

6. Design the class NameShorterThan4 that implements the ISelect interface with a method that determines whether the name in the given ImageFile object is shorter than 4.

   Make sure in the class Examples you define an instance of this class and test the method.

7. Design the method allSuch that that determines whether all items in a list satisfy the predicate defined by the select method of a given instance of the type ISelect. In the Examples class test this method by abstracting over the method allSmallerThan40000 and the method allNamesShorterThan4.

8. If you have time left, follow the same steps as above to design the method anySuch that that determines whether there is an item a list that satisfies the predicate defined by the select method of a given instance of the type ISelect.