CS2340 Homework #1

Setup:

Download and install Cincom Visualworks Smalltalk http://smalltalk.cincom.com/index.ssp

 

Part 1: 

  1. Go to the class swiki and create a page for yourself in the Who’s Who portion of the website.
  2. While Smalltalk is a “pure” OO language (everything is an object), Java is not.  Java has primitives like int and float.  This makes the design of the API non-OO in many areas.  Take a look at the Java API for the Math class with all its static methods.  How would this API be implemented in Smalltalk? Just pick 1 method (like abs) and give an example of how it would be implemented in Smalltalk? (What class would it be in, and give an example of a call, you do not need to write the implementation code)  Hint: think about factorial example we did in class.

 

Part 2:

  1. Let’s play a little with Smalltalk.  Double-click your icon for Visualworks (or use Programs->Visualworks->VisualNC.  For Linux and Mac users, you should see similar startup options after install.
  2. You should have 2 windows: One titled Workspace and one titled Visualworks NonCommercial.  Let’s backup our image first.  Go to the File menu and select Save Image As…  Give your image the name working.  Anytime your image becomes corrupted, simply reload your orginal Visualworks image to “start over”.  Modify your startup icon to use working.im instead of visualnc.im.  This leaves visualnc.im as your original clean image.
  3. Now let’s play with some operations.  Go to the Workspace window.  If you accidentally closed this window, you can launch another by going to the Visualworks main window and select the Tools menu and then Workspace.
  4. You may type the entries in Part 3 by hand into the workspace, or you may load a saved file that has all the entries pre-typed.  To do this, in the workspace window select File->Open.  Then load the Homework1.ws file.  You should see a new tab appear in the workspace with the entries below filled out.

 

Part 3:

For this section, type in (or select the appropriate lines) and select PrintIt to see the actual answer.  For each line, FIRST write out what you think the answer will be, then PrintIt (or DoIt is specified) and record the actual answer.

 

Smalltalk Code

Expected

Actual

5 - 3 * 2

 

 

‘Bob’ class

 

 

2 * 2 - 1 factorial

 

 

10 between: 2 factorial + 3 and: 20

 

 

'cs','2340'

 

 

#(a b c) inspect (Do It)

 

 

|a| a := 5.  a negated.

 

 

a := a + 6.

 

 

Highlight both the above lines and PrintIt (ignore dialog)

 

 

‘’ notNil

 

 

‘burdell’ at: 1

 

 

‘buzz’ size

 

 

|v| v:= #($p $o $c $k) as Array. (v at:1 put: $s). v.

 

 

Transcript show: ‘I like’; cr; show: ‘Smalltalk’.  (DoIt) (Look for result in Transcript Window)

 

 

 

 

 

 

Part 4:

Defining our first class.

  1. In the Visualworks window, select Browse->System.
  2. The System browser will be the main window that you use to create and edit classes and methods.
  3. There are four listviews in the middle of the browser.  From left to right, these are the Package, Class, Protocol and Method views.  Scroll down the Package view until you see the (none)* package.  This should be the last entry in the view.
  4. Click on the (none)* package and the bottom portion of the window should change to 5 tabs: Source, Properties, Comment, Rewrite and Critic.
  5. For now, we will care only about the first 3.  Select the source tab.  In the Source window, you can see a stubbed out dummy class.  You can edit this entry to create your own class if desired.  Otherwise, you can use the wizard.
  6. Let’s use the wizard.  Position the mouse pointer over the second list view from the left (our class list) and right-click select New Class.
  7. In the third box down (labeled name) type in MyFirstClass as the name of your class.  In the fifth box down (labeled instance variables) type in v1.
  8. Now hit OK.  Look in the source window, and you can see the definition of your class.
  9. Click on the Comment tab, and you can enter comments that describe your class.  You can see some are stubbed out already.  Replace the Default Comment (first two sentences) with your own comment.
  10. Click the Hierarchy tab.  You can see a graphical representation of the inheritance structure of your class.  Since we just accepted the default of Core.Object, we see that we inherit from the standard root object.  This is similar to java where everything inherits from java.lang.Object.
  11. Now let’s look at some methods.  Click on the Protocol initialize-release.  Recall that protocols are simply ways to organize our methods into logical groups.  You can see all the methods in this protocol.  In this case, there is one method initialize.  If you select initialize, the Source window will show you the code.  This code was auto-generated by our class creation wizard.  It basically initializes our instance variable to nil.  Change the nil to 1235 and press ctrl-S to accept.  Now click the accessing protocol.  Here we find all the “getters/setters” grouped together.  Again these are auto-generated by the wizard for all our instance variables.
  12. To create a new Protocol, position the mouse cursor in the protocol window and right-click.  Then select New…  In this window, you type any name you wish.  There are some pre-existing names that are somewhat “standard” in the smalltalk world.  These will pop up based upon the letters typed.  You may choose one of these, or continue typing your new name.  Let’s make a protocol named converting.  Since there is already one of these, just type ‘c’ in the listbox and then select converting and click OK.
  13.   To create a method, we first select a Protocol to put the method in.  Select (converting).  It is in italics and surrounded by parens to show that there are no methods currently in the protocol.   When you select the protocol, the Source window will contain a stubbed out version of a method.  Delete the placeholder “message selector and argument names” and type in asInteger.  The next line is comment (since it is between double quotes).  You can replace that comment with anything you like.  We do not need any local variables so delete the temporary variable lines.  Finally, replace the statements line with ^v1.  Press Ctrl-S to accept the changes.  This will commit your code to the image. 
  14. Now return to the Workspace.  In the workspace area type:  |c| c:= MyFirstClass new. c asInteger. And select PrintIt.
  15. Record the answer here:_______________

 

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