Programming Assignment 5 – Arrays and Main

In this assignment, you will get practice with writing methods that calculate values from arrays using loops.

You’ll also practice making a screencast in preparation for the take-home screencast exam.

Different assignments in this course have different collaboration policies. On this assignment, you can collaborate with anyone in the course, including sharing code. In your submission, give credit to all students and course staff who helped you with this assignment by noting their name and how you used their ideas or work. Note that using someone’s work without giving credit to them is a violation of academic integrity.

We’ve added a CREDITS.txt to note others you worked with.

The starter code is available at:

https://github.com/ucsd-cse11-s20/pa5-starter

Note that we also added some new methods after lecture Thursday, you may find some useful ideas here:

https://github.com/ucsd-cse11-s20/10-Variable-Update-Loops

FAQ

In your CREDITS.txt file, give credit to all students and course staff who helped you with this assignment by noting their name and how you used their ideas or work.
Can we use in this PA instead of loops?
- Piazza @475 “In general in this course I try to avoid saying you strictly can’t use something in the programming assignments. That’s a bit artificial. Rather, I try to design assignments where using the things we learned most recently would be the best and most natural choice for the implementation. That said, if you know something you want to try, that’s fine. Just be warned that it might be more work to not use the stuff we just learned – it was definitely the case that there were submissions to PA4 that did much more complex things than necessary for Fraction and WholeNumber using features we didn’t discuss in class.” - Joe
I wrote test methods with the Tester, but ./run is telling me that no tests ran.
- Tester methods have to start with “test” at the beginning! For example, boolean testAdd(Tester t) { …. }. In ArrayExamples.java, all tests should be in class ArrayExamples, not Pair.
I failed some tests on Gradescope, but it is not showing me any error message, so I don’t know what is wrong.
- We did something slightly different with this autograder. For each method we wrote several tests but only publicly show you some of their results in detail. The goal is to give you a nudge to think more about detailed tests you could write for your own methods. So you can see where you failed and all you know (for now) is that you should try testing and understanding those methods more.
My earliest method’s tests on Gradescope are not passing.
- Double check your understanding of compareTo method. Try using compareTo with longer strings and seeing the result. Does the method always return 0, -1, or 1?
I am receiving an array index out of bounds error in Longest.java.
- Unlike some of the previous method, you can not make the assumption that string argument(s) will be given. Hence, args[0] will throw the index out of bounds error. What is a possible way to check if any arguments are given?
Help! I did the conditional checking and Longest.java is still throwing index out of bounds!

Consider the following: if (...){ // inside for loop } // after for loop Recall that regardless if the if statement runs or not, the code beneath the if statement will run if not wrapped in an else statement. An else statement may be useful in avoiding the index out of bounds error.

Array Methods

In a file called ArrayExamples.java, write the following methods in a class called ArrayExamples. For each, write three tests (a test is a use of checkExpect) where each of the three has a different length of array used in the input.

Write a method called joinWith that takes an array of String and a String separator, and returns a new String that contains the strings from the array separated by that separator. For example, for an array containing "a", "b", and "c" with separator ":", the result would be "a:b:c" (note that there’s no colon at the end, just in between the elements). If the input array is empty, produces the empty string.
Write a method called allTrue that takes an array of boolean and returns true if all the elements in the array are true. If the array is empty, produces true.

“Inclusive” is another way of saying to use ≤ instead of < and ≥ instead of >

Write a method called allWithinRange that takes an array of double and two other doubles called low and high, and returns true if all of the numbers in the array are between low and high (inclusive). If the array is empty, this should produce true. You can assume that low ≤ high
Write a class called Pair with two int fields, a and b, and include a default constructor. (Add Pair at the top level, outside the ArrayExamples class). Then write a method (in ArrayExamples, not in Pair) called maxmin that takes an array of int and returns a Pair where the a field is set to the smallest integer in the array and the b is set to the largest. Assume the array has at least one element.

Computer scientists have a fancy name for alphabetical: lexicographic. You will need the compareTo method on Strings here. Try it out on a few examples if you're not sure what it will do!

Write a method called earliest that takes an array of Strings and returns the String that is the earliest alphabetically. You can assume that the array has at least one element.
Write a method called lookup that takes an array of String called keys, an array of int called values, and a String called key (three total parameters). It should find the index in keys where the argument key appears, and then return the int stored in values at that index. If the key is not found, the method should return -1. You can assume that lookup will always be given two arrays of the same length, and that there are no duplicate strings in keys.

Example: keys contains "UCSD", "UCLA", "UCI" and values contains 36000, 44900, and 33467. For key "UCI", it should return 33467. For key "Stanford", it should return -1.

Using Main and Command-line Arguments

In a file called Longest.java, write a class called Longest. It should have a main method which prints out the longest string in the command line arguments. If no arguments were given, it should print nothing. Example:
```
$ javac Longest.java
$ java Longest which argument is the longest
argument
$ java Longest one two three four
three
$ java Longest
$
```
You can assume that there is not a tie for the longest string’s length.
In a file called Stats.java, write a class called Stats. It should have a main method which has a different effect depending on the first command line argument. In all cases, it can assume that there will be at least two command-line arguments, and all the arguments after the first are appropriate arguments to Double.parseDouble. If the first argument is …

When comparing Strings, the == operator can be unreliable. Instead use .equals or .compareTo, which are in the Java String documentation.

"--product", print the product of the provided numbers
"--mean", print the average (mean) of the provided numbers
"--total", print the sum of the provided numbers
"--max", print the maximum of the provided numbers
"--min", print the minimum of the provided numbers
any other string, print "Bad option <arg>" where you will replace "<arg>" with the first argument

Examples:

  $ javac Stats.java
  $ java Stats --product 2 3 4
  24.0
  $ java Stats --mean 5 9 7
  7.0
  $ java Stats --total 1 9 4
  14.0
  $ java Stats --max 9 1 4 0
  9.0
  $ java Stats --min 9 1 4 0
  0.0
  $ java Stats --mix 3 4 5
  Bad option --mix

Practice Screencast

For the take-home exams, you’ll be recording a screencast that demonstrates your programs. The last part of this PA has you practice with this.

You will record a short video (no more than 2 minutes). Include:

Your face and your student ID for a few seconds at the beginning. You don’t have to be on camera the whole time, though it’s fine if you are. Just a brief confirmation that it’s you creating the video and doing the work attached to the video.
A capture of your screen running your Longest program. Make sure the code of Longest.java AND your terminal output are shown in the video
Show running the two examples of Longest above, with their results clearly visible in the terminal

We’ve made a short tutorial demonstrating how to make a screencast with Zoom:

Screencast Tutorial

The associated video that was created is here:

Example Result

You don’t have to make your screencast with Zoom, but Zoom is UCSD-licensed software that you have access to, so we offer the tutorials with that in mind.

Please do reach out if you run into issues with this, and try something out early so you know if it will work or not for you – you’ll need it for the exam!

Submission

You will upload your video file to this link:

Upload Form

All of your Java files you will upload to Gradescope as usual.