Outline of Class 12: Tools

Miscellaneous

• A reminder that majors should see Mr. Imig to have your pictures taken for the majors' board.
• The reading on greedy algorithms is almost ready.
• For the first part of assignment four you only have to recreate your fellow student's main routine (although you will do so in a separate class).
• Tony and Omar will be presenting on Monday instead of Friday.
• Anyone who hasn't made their directory readable (Kevin N., ...) better do so asap.
• We'll spend some time today discussing a few Java issues that you seem to be having probems with.
• I've made some fairly significant modifications to the syllabus. We'll be doing algorithms next week, instead of this week; and doing make this week instead of next week.

Java, Revisited

• In helping some of you folks (and hearing from Andrew about some of the more common problems), it seems that there are a few more things that we need to cover in a little more depth.
• Don't initialize non-static fields when you declare them. Initialization (particularly initialization that involves allocation) should be done in your constructor.
• Remember that static (also known as "class") variables and methods are associated with the class as a whole (although they can also be used in conjunction with individual objects).
  • You need not create objects (instantiate the class) to use static variables and methods.
  • All the objects in a class share the static variables, so a change in one will affect all objects.
• Non-static methods and fields can only be used in conjunction with objects.
  • You must create objects to use these methods and fields (even if you're working within the same "class").
  • Within a non-static method, you can refer to other non-static methods and fields.
  • Within a static method, you need to create an object in order to use that object's non-static methods and fields.
  • Your main method is a static method. You can, however, create objects in the current class for use iwthin that method.
• In creating constructors for subclasses, you will often want to call the constructor of the superclass. The constructor for a superclass is called super(...).
• An odd coding tip. Rather than doing comparision with
  var == value
  consider using
  value == var
  (so that it won't compile if you mistakenly use one equal sign instead of two).
• There's a link to the standard Java API in my home directory.

More RCS

RCS fields

• Since RCS keeps track of a number of things, such as the author of the latest version of your code (and even the "number" of the latest version of your code), there's no reason for you to have to hand-code that information.
• RCS permits you to insert a number of keywords of the form $keyword$ in your code, and replaces them with $keywork: value$.
• Particularly useful ones are $Revision$ and $Date$.
• I'd caution against using $Author$ as that only gives you the author of the latest revision.
• Other keywords are documented in the man page for co.

The RCS version tree

• Even with the most modular design, there will be times that more than one programmer will need to work on the same file (but hopefully on different parts of the same file).
• There are also times that you might want to try different extensions to the same piece of code.
• RCS supports version trees to accomodate these and similar instances.
• The tree is given by the numbering hierarchy.
  • The main branch of the tree has versions of the form a.b
  • Primary branches have versions of the form a.b.c.d
• To start a new version tree, use the -r option when you check in a file. If you give three parts (e.g., a.b.c) to the version number, it should start a new branch of the form a.b.c.1
• You can use rcsmerge to merge in changes to a document and rcsdiff to compare two versions.
• Unfortunately, rcsmerge doesn't seem to work with the fields mentioned above (at least in my tests). That is, if you use the fields in comments, rcsmerge chokes.
• The form of rcsmerge is a little odd.
  rcsmerge -rrev1 -rrev2 file
  finds the changes between rev1 and rev2 and then makes those changes to the current version of the file (which should be checked out).
• You can learn more about the rcs version tree by looking at the man page for rcsfile.

An exercise with rcsmerge