Programming Assignment 5 – Arrays and Main

Due Tuesday November 2 10:00pm Pacific Time

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

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.

The starter code is available at:

The check-off instructions (with some new updates) are here:


Submit the following files to Gradescope in the PA5 assignment:


  1. Can we use a library or built-in method in this PA instead of loops, even if we haven’t seen it in class?
    • In general in this course we try to avoid saying you strictly can’t use something in the programming assignments. That’s a bit artificial. Rather, we 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.
  2. 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, all tests should be in class ArrayExamples, not Pair.
  3. I am receiving an array index out of bounds error in
    • Unlike some of the previous methods, 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?
  4. Help! I did the conditional checking and 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, 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, one of which tests an empty array (if it is allowed as an input). All of these methods should be static.

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

Below are a few tests to get you started. We designed these to work on their own in a separate class. You must include them all in your final submission (it helps us check that basic things work when reviewing your code). But these tests don’t cover all cases, which is why you must write your own as well.

To confirm that all the tests (yours and ours) are passing, include a file array-transcript.txt showing the result of running the run commands for both sets of tests.

import tester.*;
class ProvidedArrayExamples {
  void testJoinWith(Tester t){
    String[] example1 = {"a", "b","c"};
    t.checkExpect(ArrayExamples.joinWith(example1, ":"), "a:b:c");

  void testSomethingFalse(Tester t){
    boolean[] example1 = {true, false};
    t.checkExpect(ArrayExamples.somethingFalse(example1), true);

  void testCountWithinRange(Tester t){
    double[] example = {0.1, 1.3, 2.6};
    t.checkExpect(ArrayExamples.countWithinRange(example, 1.1, 2.2), 1);

  void testNumsWithinRange(Tester t){
    double[] example = {0.0, 3.0, 1.4, 1.5, 2.7, 9.1, 2.1};
    double[] expected = {1.4, 1.5, 2.1};
    t.checkExpect(ArrayExamples.numsWithinRange(example, 1.1, 2.2), expected);

  void testMaxmin(Tester t){
    int[] example = {4, 5, 2, 3, 1};
    t.checkExpect(ArrayExamples.maxmin(example), new Pair(1, 5));

  void testEarliest(Tester t){
    String[] example = {"aa", "aab", "abcd", "a"};
    t.checkExpect(ArrayExamples.earliest(example), "a");

Using Main and Command-line Arguments

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


  $ javac
  $ java Stats --product 2 3 4
  $ java Stats --mean 5 9 7
  $ java Stats --total 1 9 4
  $ java Stats --max 9 1 4 0
  $ java Stats --min 9 1 4 0
  $ java Stats --mix 3 4 5
  Bad option --mix

Also create a file called stats-transcript.txt that shows your Stats program called with the examples above and, for each one of the operations, threee uses of that operator with inputs of your own design where one use has only a single number provided. Copy/paste the output from your terminal to make this file.

Extra Challenges (Not for Credit)