Overview

• Preliminaries.
  • Upcoming work.
  • Admin.
  • Questions.
• Anonymous inner classes - the concept.
• Anonymous inner classes - the implementation.
• Some subtleties.
• Lab.

Preliminaries

Upcoming Work.

• Homework 5 is due next Wednesday (March 5), but you may need two weeks to get it done.
• The exam makeup is due Sunday at 10:30 p.m. There will be no extensions.
• No reading for tomorrow.
• Lab writeup (whoops, coming soon)

Admin

• MathLAN may or may not be acting up again. Yesterday morning was backups left over from the weekend. I'm not sure what last night was, or what today will bring.
• I took off 1/4 point for incorrect tarballs. A few of you talked to me about it and I accept that for the first exam, a bit of carelessness or confusion is possible. I will restore those points if you show me that I took them off.
• Review session tonight at 7pm
• Extra credit:
  • Town hall meeting Today at noon or 7:30pm.
  • Wellness fair, around the JRC, 5:30-8:00 pm
  • CS Extras, Thursday at 4:30 p.m.: The new CS Curriculum.
  • More?

Questions

Anonymous inner classes - the concept

Sometimes you want functions and it's not worth your time/effort to name them.

(set! grades (map (l-s + .25) grades))

vs.

(define fixgrade
  (lambda (x) (+ .25 x)))
(set! grades (map fixgrade grades))

First is shorter

Giving something a name takes mental energy and pollutes the namespace.

In Java, anonymous things are also useful

• When sorting, we need a way to compare values
• When searching, we need a way to determine if we've found the desired value
  • And we may need to build values on the fly.

In Java, anonynous is particularly useful because we have to write a lot when we declare a new class.

Java has anonymous classes

We use them to provide the functions that we need above.

Anonymous inner classes - the implementation

new Interface() { Method implementations }

E.g.,

public interface Checker { public boolean okay(Object o); } // interface Checker

public class Sam { public static Object search(Object[] values, Checker check) { for (v : values) if (check.okay(v)) return v; } // search(Object[], Checker) } // class Sam

Sam.search(students, new Checker() { public boolean okay(Object o) { return o.toString.contains("k"); } // okay } // Checker );

public class SamR { public static Object searchByString(Object[] values, final String str) { Sam.search(students, new Checker() { public boolean okay(Object o) { return o.toString.contains(str); } // okay } // Checker ); } } // class SamR

Some subtleties

• How do you deal with fields?
• How do you deal with fields of the enclosing object?
• How do you deal with parameters of the enclosing method?
• Can we do this with subclassing, too?