Held: Wednesday, 1 October 2014

Back to Outline 19 - Java Generics. On to Outline 21 - Anonymous Inner Classes.

Summary

We consider the ways in which you build and use anonymous functions in Java (or at least Java 8).

Related Pages

• Lab: Anonymous Functions
• Github Repo: https://github.com/Grinnell-CSC207/lab-anonymous-functions
• Java Tutorial on Lambdas: http://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html
• Documentation for Predicate interface: http://docs.oracle.com/javase/8/docs/api/java/util/function/Predicate.html

• Documentation for Function interface: http://docs.oracle.com/javase/8/docs/api/java/util/function/Function.html

• EBoard 20 (Source 20) (HTML 20)

Overview

• Anonymous Functions
• Anonymous Functions in Java
• More About Functional Interfaces
• Useful Functional Interfaces

Administrivia

• Continue lab partners.
• Office hours this week (modified due to meetings):
  • Thursday 8:00-9:45, 2:30-3:15
  • Friday 2:15-3:15
• A note from yesterday evening's tutor: "In Java, one student's procedure was throwing an exception, and then apparently continuing on to run the rest of his code anyway. We couldn't figure out why this was happening." Anyone want to talk to me about this?
• I appreciate that I'm teaching anonymous procedures in both 151 and 207 today. I hope that you do, too.

Upcoming Work

• HW 7 assigned.
• Readings for Friday:
  • Anonymous Inner Classes
  • Java Tutorial/Inner Classes: http://docs.oracle.com/javase/tutorial/java/javaOO/innerclasses.html
  • Java Tutorial/Local Classes: http://docs.oracle.com/javase/tutorial/java/javaOO/localclasses.html
  • Java Tutorial/Anonymous Classes: http://docs.oracle.com/javase/tutorial/java/javaOO/anonymousclasses.html

Extra Credit Opportunities

Academic

• CS extras Thursday: Alumni
• CS table Friday: Serendipity and Computing (with Grinnell's Artist in Residence)
• Grinnell Prize Events the following week

Peer Support

Miscellaneous

Anonymous Functions

• Context: We have operations that naturally take a function as input.
  • map often takes a unary function and a list.
  • reduce often takes a binary function and a list.
  • sort often takes a comparator and an array.
• Basic idea: Sometimes it pointless to name to function (particularly in an OO language, in which the function may be modeled as a class).
• Expanded idea: Sometimes you need a function that uses a local resource, and it's a PITN to do the extra work. (Scheme does this better than Java.)
• It's an idea as old as Lisp (so 1958), but just added to Java.

Anonymous Functions in Java

• Introduced in Java 8.
• Typically implement a "functional interface".
  • An interface with only one method.
  • Should include the annotation @FunctionalInterface
• Syntax
  • (PARAMS) -> EXPRESSION
  • (PARAMS) -> { BLOCK }
  • PARAM -> EXPRESSION
  • PARAM -> { BLOCK }

More About Functional Interfaces

• Functional interfaces can also include default methods. These methods are implemented in the interface (thereby changing how we think of interfaces).
  • We now have some issues with multiple inheritance, but that's life.
• Functional interfaces can also include static methods.

Useful Functional Interfaces

• java.util.function.Predicate
• java.util.function.Function