a. Review the documentation for the Predicate interface, available
at https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/function/Predicate.html.
b. Review the documentation for the Function interface, available
at https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/function/Function.html.
c. Review the documentation for the Comparator interface, available
at https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/Comparator.html.
d. Open the Java Tutorials page on lambda expressions.
e. Fork and clone the repository at https://github.com/Grinnell-CSC207/lab-anonymous-procedures.
f. Review the code in the repository.
e. Create a new class, ListUtils, that you will use for some of the exercises.
Driver: Alternating
In the section entitled “Ideal Use Case for Lambda Expressions” in
the reading, the authors present nine different approaches to
filtering a list. Write a program that experimentally verifies
that each of the nine approaches works as described. You will do
this in JTLambdaExperiments.
You will likely need to
Person class associated with the reading, which is available at https://docs.oracle.com/javase/tutorial/java/javaOO/examples/Person.java.main method of JTLambdaExperiments, create a list of Person objects. (We’d recommend an ArrayList.)
You can see the createRoster method in Person for an example.JTLambdaExperiment and then add a call to that method to main to see that the method behaves as expected.Note: If you are adding interfaces and classes, you should do so outside
the body of JTLambdaExperiments.
Note: I apologize for the sex binary in the Person class.
Driver: B
a. In ListUtils, write a static generic method, select(List<T>
vals, Predicate<T> pred), that creates a new ArrayList<T> that contains
only the elements of vals for which the predicate holds.
b. In the main method of LambdaExperiments, select and print
the values in strings whose length is at least five. Make sure
to define your predicate using a lambda.
c. In the main method of LambdaExperiments, select the values
in strings which contain two vowels in a row. Once again, make
sure to define your predicate anonymously.
Driver: A
Rather than building a new list by selecting values, as in the previous problem, we could also write a method that mutates an existing list by removing values.
a. In ListUtils, write a static generic method, remove(List<T>
vals, Predicate<T>), that removes from vals any values for which
the predicate holds. You may not use any existing methods in the
List class other than iterator. You can assume that the remove
method is implemented in the given iterator.
b. Extend your program to remove the values in strings whose length is
at least five.
c. Extend your program to instead remove the values in strings which contain two vowels in a row.
Driver: B
Another common generic task is to find the largest (or smallest) value in a list.
a. Write a static generic method, largest(List<T> vals, Comparator<T>
compare), that finds the largest element in the list, using compare
to compare values.
b. Extend your program to find the shortest string in strings. (If
there are multiple shortest strings, you can return any of them.)
c. Extend your program to find the longest string in strings. (If
there are multiple longest strings, you can return any of them.)
d. Extend your program to find the string in strings whose sum of
ASCII values is the smallest.
e. Extend your program to find the string in strings whose sum of
ASCII values is the largest.
In the unexpected situation that you find that you have extra time, you might attempt one or more of the following exercises.
a. Implement a static generic method, map(Function<T,R> fun, List<T>
vals) that builds a new ArrayList<R> by applying fun to each element
of list.
b. Using map, build a new version of strings in which every string is converted to uppercase.
c. Using map, build a new version of strings in which the first letter in each string is converted to uppercase.
d. Using map, build a new list that contains the lengths of all of the
strings in strings.
The Java Tutorials page for lambdas notes that
The Java Tutorials have been written for JDK 8. Examples and practices described in this page don’t take advantage of improvements introduced in later releases.
Determine what improvements have been added in later releases.
Find at least two other functional interfaces and describe use cases for those interfaces.
Lambda provide a nice alternative to anonymous inner classes, with a bit less syntax. Can we use lambda to implement iterators? Why or why not?
Some problems on this lab were inspired by a lab on anonymous procedures from the Fall 2014 iteration of CSC 207.