SE450: Homework 2

The basics.

• Download the homework files from D2L, as explained here.
• Complete the files in the src directory correctly.
• Upload the homework files to D2L, as explained here.
• You can view the source code online here [source].

Notes

• Not that much has changed from hw-01.
  • There are three packages:
    • myhw2.data holds the inventory (Public javadoc) (Private javadoc)
    • myhw2.command holds the command interface -- more here next week. (Public javadoc) (Private javadoc)
    • myhw2.main holds the integration test -- more here next week.
  • There are interfaces for Video, Inventory and Record.
  • The inventory object classes are all package-private.
  • The static factory Data provides access to inventory objects.
  • The inventory interface has changed substantially:
    • toCollection has been replaced with two iterator methods: one is an unsorted iterator, the other uses the strategy pattern to return a sorted iterator.
    • The mutator methods of the inventory are all package-private.
    • To modify the inventory from outside the package, one must invoke the run method, passing in a Command object. See the example in file:myhw2/main/TEST1.java [source] [doc-public] [doc-private].
  • RecordObj is a nested class, emphasizing its dependence on InventorySet.
  • Since record objects are protected behind the public interface Record, it is no longer necessary to copy them -- they canot be modified outside the myhw2.data package.
• Complete the incomplete classes (you may wish to paste in some of your hw-01 solution).
• Modify your unit tests so that they pass. (There is no longer any need to test Record).
• Write the integration test myhw2.main.TEST1.

A nice way to generate an integration test (like myhw2.main.TEST1):

+ write a driver with some print statements, like this:

    System.out.println(Data.inventory().get(v1));

  which may output something like

    Title1 (2000) : Director1 [10,0,0]

+ read the output to check it and make sure it's okay

+ then replace the System.output with an assert:

    Assert.assertEquals("Title1 (2000) : Director1 [10,0,0]",
                        Data.inventory().get(v1).toString());

Now you can run the test over and over and it will make sure that the
output is always what you got the time you checked it.

For InventorySet.iterator(), it's easy just return
Collections.unmodifiableCollection(_data.values()).iterator();

For InventorySet.iterator(Comparator c), it is a bit more delicate.
Here's one way:

 + Create a separate copy in a list, for example
   List l = new ArrayList(_data.values())
 + Sort the list using Collections.sort(List,Comparator)
 + Return an iterator over the sorted list

How to test
InventorySet.iterator(), where we don't know the order...

 + Create a local HashSet<Video> and an InventorySet.
 + Put some videos in the InventorySet.
 + Put corresponding Videos in the HashSet.  Use Video, not Record,
   since you cannot create records directly.  You could also use
   strings such as "Title1 (2000) : Director1 [10,0,0]"
 + Now call InventorySet.iterator() and go through the elements.
   For each record returned do the following:
     ++ Make sure an equivalent video is in the local HashSet
     ++ Remove the equivalent video from the HashSet
 + Once you're done with the iterator, make sure the local HashSet is
   empty.

To test InventorySet.iterator(), where we do know the order ...

 + Create class that implements Comparator.  When called, the
   arguments will be Records.  For example, the following class will
   compare Records based on the number owned:

   Class NumOwnedComparator implements java.util.Comparator {
     public int compare (Object o1, Object o2) {
       Record r1 = (Record)o1;
       Record r2 = (Record)o2;
       return r2.numOwned() - r1.numOwned();
     }
   }

   or use the following in Java 1.5 to get rid of "unchecked
   conversion" warnings:

   class NumOwnedComparator implements java.util.Comparator<Record> {
     public int compare (Record r1, Record r2) {
       return r2.numOwned() - r1.numOwned();
     }
   }

 + Continue as before, but this time use a List to keep the videos in
   expected order.

If you want some more reading about Comparators/Comparable see:
Making Java Objects Comparable
by Budi Kurniawan
http://www.onjava.com/pub/a/onjava/2003/03/12/java_comp.html

Here is one scenario --- running an add command --- from line 31 of
myhw2.main.TEST1:

00029:     Video v1 = Data.newVideo("Title1", 2000, "Director1");
00031:     Assert.assertTrue(Data.newAddCmd(_inventory, v1, 5).run());

The objects involved are:

  +-----------+  +----------------+  +------------------+  +--------------+
  | t : TEST1 |  | c : CmdAdd     |  | i : InventorySet |  | v : VideoObj |
  | --------- |  | ----------     |  | ---------------- |  | ------------ |
  +-----------+  +----------------+  +------------------+  +--------------+
                 | inventory = i  |   
                 | video = v      |   
                 | change = 5     |
                 +----------------+

Execution proceeds as follows:

  t calls c.run();
  c calls i.addNumOwned(v,5)

Revised: 2008/01/22 15:43