Higher-order Function Filter Assignment

Motivation

In this studio you will be building the first ballot inductee to the Dan Grossman Hall of Fame of Higher Order Functions: filter.

This studio will give us the opportunity to work with the standard Java for-each loop, generics, interfaces, and lambda expressions.

With filter we get to use the for each loop and invoke a method on a generic type interface.

With filterEvens and filterWordsWhichContainAll5Vowels we get to invoke filter with lambda expressions.

Background

• Java for-each loop
• generics
• interfaces
• lambda expressions

Mistakes To Avoid

Warning: In implementing filter, do NOT mutate the list passed in as a parameter. Return a new list with the items which pass the predicate's test.

Warning: Do NOT re-implement the filter functionality in filterWordsWhichContainAllVowels and filterEvens. Invoke the filter method you just wrote.

Code to Implement

filter

class:	FilterUtils.java
methods:	filter
package:	hof.filter.group
source folder:	student/src/main/java

method: public static <E> List<E> filter(Predicate<E> predicate, List<E> list) (sequential implementation only)

This classic high level function returns a list with the elements of list for which predicate's test method returns true. The predicate's test method is applied to each element in order.

clients

class:	FilterClients.java
methods:	filterEvens filterWordsWhichContainAll5Vowels
package:	hof.filter.group
source folder:	student/src/main/java

We created a couple of utility methods which invoke filter with a custom lambda.

filterWordsWhichContainAll5Vowels

method: public static List<String> filterWordsWhichContainAll5Vowels(List<String> words) (sequential implementation only)

Useful method: str.indexOf(ch)

filterEvens

method: public static List<Integer> filterEvens(List<Integer> xs) (sequential implementation only)

Testing Your Solution

Correctness

class:	_FilterTestSuite.java
package:	hof.filter.group
source folder:	testing/src/test/java