Homework 08 (Due 11:00am Friday, March 13, 2009)

Preliminaries

This homework on manipulating Java lists must be done using the Intermediate language level of DrJava. We are providing skeleton classes for each problem with unimplemented methods for you to write. Each such class includes a method with a name like listString() that converts lists to more readable String notation similar to that used in Scheme.

Composite Design Pattern for List

1. Write the arrangements (permutations) function from problem HTDP problem 12.4.2 in HW2 as a Java method for a Word class provided in the file Word.dj1. This file includes definitions of the composite pattern classes Word and WordList. Decompose the problem in exactly the same form as the posted solution to problem 12.4.2 (see the HW2 entry in the course calendar on the main wiki page). We are providing skeletons for the classes Word and WordList in the file WordList.dj1; use them.

2. Write the mergesort function from the last problem in HW4 (using exactly the same top-down approach described in HW4) as a Java method in the composite pattern class ComparableList provided in the file ComparableList.dj1.

3. Do Exercise 21.2.3 from HTDP using the Java composite pattern class ObjectList provided in the file ObjectList.dj1. This file includes the interface Predicate, which is the type of Java function arguments passed to the filter method, and abstract method stubs for filter, eliminateExp, recall, and selection. Exercise 21.2.3 provides Scheme code for the filter function which you should directly translate to the corresponding Java method code in ObjectList. Note that your filter method should work for arbitrary ObjectLists. In coding the methods eliminateExp, recall, and selection, use the Java type Number (compared using method doubleValue) in place of the Scheme number type and the Java type Object in place of the Scheme symbol type. The method doubleValue() in Number returns the value of this converted to a double. You will need to cast the Object input of the test method to type Number when filtering lists of numbers.

4. Do Problem 2 from Homework 5 in Java using the composite hierarchy of classes provided in the file ArithExpr.dj1. (Make sure that download the current version of ArithExpr.dj1; an early version declared Env as an interface rather than an abstract class.)