Outline of Class 6: Lab: Building Classes

Held: Tuesday, January 27, 1998

Administrivia

• The Grinnell Review is seeking submissions of academic papers (research, essays, etc.) for publication in the 1997-98 edition of the magazine. The papers can be about any topic, so long as they are of general interest. All members of the Grinnell community are invited to submit their work. Send submissions to box 09-26 by February 20th. Vax [REVIEW] with any questions.
• It was good to see a few of you at the brown bag lunch yesterday. I hope to see more of you next week.
• This Thursday, the department is showing some interesting mathematical movies. See the signs around the department for more information.
• Don't forget that the exotic programming languages discussion groups starts meeting today at 4:15 pm.
• Any questions on assignment 1?
• Any questions on assignment 2?

Standard Methods

• Many Java programs assume that your classes include a particular set of commonly needed operations. These include
  • public boolean equals(Object obj) -- determine whether another object is the same as the current object.
  • public int hashCode() -- convert the object to an integer (the conversion does not need to be undoable) so that different objects tend to convert to different integers and equal objects always convert to the same integer.
  • public String toString() -- convert the object to a printable representation. This is used whenever (more or less) you try to use the object as a string (e.g., when you concatenate it to a string or print it).
• There is also an optional method that most classes include. If you include this, you note that your class implements Cloneable.
  • public Object clone() -- make a copy of the current object.
• We'll look at how to write these different methods for a sample class.

Laboratory Exercise

Do lab 2.