CSE 331 - HW Setup Homework 2: Environment Setup, Reasoning and Debugging Due: Wednesday, April 13 at 11:00 PM Contents: Part 1: Verifying Correctness Part 2: Choose a Development Environment Part 3: Obtaining files from GitLab Part 4: Fix Buggy Code—HolaWorld Editing and Compiling Source Files Fixing HolaWorld Part 5: A new Java class—RandomHello No Need to Reinvent the Wheel Using java.util.Random Part 6: Testing Java Code with JUnit Part 7: Answering Questions About the Code Part 8: Debugger Tutorial Part 9: Implementing Code with Invariants— Finder and Evaluator Implementing Variants of Finder Implementing Variants of Evaluator How to Turn In Your Homework The purpose of this homework is to help you set up your development environment, get reacquainted with Java, and start getting familiar with tools you will use for the rest of the course. Although the homework description is long, we expect the step-by-step instructions will make doing the homework less overwhelming than reading it may be. This homework links to (the middle of) some other handouts at many points. For convenience, here is the list of these handouts: Project Software Setup Editing, Compiling, Running, and Testing Java Programs Version Control Reference Assignment Submission Google Java Style Guide (It also links to various Java files and API documentation files that are not listed above.) Part 1: Verifying Correctness We start the assignment with another code reasoning problem given in this worksheet. Note that this part of the homework is completely separate from the rest, so you are free to work on other parts before finishing this one. Feel free to rewrite the problems on a separate sheet. You do not have to turn in these exact pages with the blanks filled in (though you can do that as well). It is okay to submit a scanned copy of a hand-written document as long as it is legible, so you can also print the worksheet, write your answers on that, and scan it when done. After finishing, submit your solution as a PDF in Gradescope. Be sure to indicate in Gradescope which pages of your PDF solved which parts of the worksheet problem. The rest of the homework will have a different submission method; your PDF solution to part 1 should be the only file you submit in Gradescope. Part 2: Choose a Development Environment Read the Project Software Setup document and decide where you will do your work. Also choose what Java development tools you will use. We recommend using the IntelliJ IDE in CSE 331, but the choice is up to you. We also provide instructions for working from the Linux command line. If you choose a different IDE, you will need to figure out how to do the operations from it, or use the command line. IntelliJ is the most popular Java IDE. If IntelliJ is new to you, allocate some time to learn its features. That time will pay off — probably this quarter, and definitely in the future. Once you have chosen and prepared a development environment, you should set it up for CSE 331 use. See Configuring IntelliJ for 331 and follow any instructions that are applicable. (Note: if you switch development environments later in the quarter, revisit these instructions.) Part 3: Obtaining files from GitLab Your homework for this quarter will all be stored and tracked in a Git repository. Since this is the first time you're using this repository, you'll need to "clone" it to get a copy on your local computer. Follow the cloning instructions in the Project Software Setup handout. Also familiarize yourself with the other tools and commands listed in that document, and the concepts of Git in general. Note that, if you attended section, you've already done this with the group. Part 4: Fix Buggy Code—HolaWorld For this problem, you will fix some buggy code we provide. Editing and Compiling Source Files See Editing and Compiling Source Files to help learn how to perform the following basic tasks: adding new files to your directory structure, compiling Java code, and reading the Java compiler's output (which may indicate errors). Also read the Google Java Style Guide, which describes some standards for Java style used by Google. We expect you to have consistent, readable style throughout the quarter. This style guide may be a reasonable place to start if you're not sure how to achieve that, but we're not requiring that you exactly follow any specific part of that guide. The most important thing to have is consistent style, including style that is consistent with the starter code you may be modifying. Fixing HolaWorld Try to compile the provided code in HolaWorld.java. You should see compilation errors for this file. (And possibly in RandomHelloTest.java too; if so, ignore these for now since we will fix them in the next part.) In particular, the lines: System.out.println(world.); and: return SPANISH_GREE; are problematic. (You might see the second error only after you've fixed the first one.) If you are using IntelliJ, these errors will be marked with red squiggly lines in HolaWorld.java. Fix these errors and run HolaWorld by running the setup:runHolaWorld gradle target. See the Editing and Compiling Source Files handout for more information on running gradle targets. After you've fixed the errors and run the code, it would be a good time to commit your changes to your repository and push them to GitLab. Part 5: A new Java class—RandomHello Create a Java class with a main method that will randomly choose, and then print to the console, one of five possible greetings. Create the file RandomHello.java, which will define a Java class RandomHello that will reside in the Java package setup; that is, its file name is .../cse331-QUARTER-YourCSENetID/hw-setup/src/main/java/setup/RandomHello.java. Java requires every runnable class to contain a main method whose signature is public static void main(String[] args) (for example, see the main methods in HelloWorld and in HolaWorld). A code skeleton for the RandomHello class is shown below. IntelliJ will generate an empty class skeleton for you if you use it to create the new RandomHello class. You're welcome to use that and fill in the entire class yourself, or just copy/paste the skeleton we provide below and work from there. RandomHello.java:
package setup;
/** RandomHello selects and prints a random greeting. */
public class RandomHello {
/**
* Prints a random greeting to the console.
*
* @param args command-line arguments (ignored)
*/
public static void main(String[] args) {
RandomHello randomHello = new RandomHello();
System.out.println(randomHello.getGreeting());
}
/** @return a greeting, randomly chosen from five possibilities */
public String getGreeting() {
// YOUR CODE GOES HERE
}
}
This skeleton is meant only to serve as a starting point; you are free to organize your code as you see fit. No Need to Reinvent the Wheel Don't write your own random number generator to decide which greeting to select. Instead, take advantage of Java's Random class. (This is a good example of the adage “Know and Use the Libraries” as described in Chapter 9 of Joshua Bloch's Effective Java, 3rd edition. Learning the libraries will take some time, but it's worth it!) Add the following to the body of your getGreeting() method:
Random randomGenerator = new Random();
This line creates a random number generator (not a random number, but a Java object that can generate random numbers). In IntelliJ, your code may be marked as an error by a red underline. This is because the Random class is defined in a setup that has not yet been imported (java.lang and setup are the only packages that are implicitly imported). Java libraries are organized as packages and you can only access Java classes in packages that are imported. To import java.util.Random, add the following line under the package setup; declaration):
import java.util.Random;
This will import the class Random into your file. In IntelliJ, to automatically add all necessary imports and remove unused imports, either choose "Code | Optimize Imports" on the main menu, or type Ctrl+Alt+O to optimize your imports (documentation for optimizing imports). Because there is only one class named Random, IntelliJ will figure out that you mean to import java.util.Random and will add the above line of code automatically. (If the name of the class that needs to be imported is ambiguous — for example, there is a java.util.List as well as a java.awt.List — then IntelliJ will prompt you to choose the one to import.) Using java.util.Random Read the documentation for Random's nextInt(int n) method by going to the Java API and searching for Random using the search bar in the top right-hand corner. In IntelliJ, you can hover over the class or method name and press a hotkey to view documentation (check your IntelliJ settings/preferences, under "Keymap" to find your specific hotkey for "Quick Documentation"). Use the nextInt(int n) method to choose your greeting. You don't have to understand all the details of its behavior specification, only that it returns a random number from 0 to n-1. One way to choose a random greeting is using an array. This approach might look something like:
String[] greetings = new String[5];
greetings[0] = "Hello World";
greetings[1] = "Hola Mundo";
greetings[2] = "Bonjour Monde";
greetings[3] = "Hallo Welt";
greetings[4] = "Ciao Mondo";
The main method in the skeleton code above prints the value returned by getGreeting. So after you complete getGreeting, when the class is run the main method will print that greeting. When you are finished writing your code and it compiles, run it using the runRandomHello target several times to ensure that all five greetings can be displayed. Again, now would be a good idea to add your new class to version control, commit it, and push it. Part 6: Testing Java Code with JUnit Testing is essential for writing quality software. JUnit is a framework for creating unit tests in Java. A unit test checks that one specific, small piece (a "unit") of functionality is working correctly. (JUnit can be used to create other types of tests, too.) This problem provides a quick overview and simple example of how JUnit works. (Testing will be more significant in later assignments.) Open both hw-setup/src/main/java/setup/Fibonacci.java and hw-setup/src/test/java/setup/FibonacciTest.java. From the comments, you can see that FibonacciTest is a test of the Fibonacci class. Now run the JUnit test setup.FibonacciTest. You'll notice that it's failing its tests! Examine the test code and gradle's test output to understand why the tests are failing, then use that information to find and fix the bugs in Fibonacci so it's passing all the tests. The tests are correct, so you shouldn't modify FibonacciTest at all, but it's probably useful to look at the code and see what it's doing. Now look at the JUnit tests that we wrote for HolaWorld and RandomHello. They are called HolaWorldTest and RandomHelloTest, respectively. Ensure that your modified code passes these tests before you turn in your homework. Part 7: Answering Questions About the Code Locate the answers.txt file in your repo; you'll find it in hw-setup/src/main/java/setup/. In that file, write your answers to the following questions using a few sentences max for each question. Why did Fibonacci fail the testThrowsIllegalArgumentException test? What (if anything) did you have to do to fix it? If you did not have to change anything to fix this issue, explain why. Why did Fibonacci fail the testBaseCase test? What (if anything) did you have to do to fix it? If you did not have to change anything to fix this issue, explain why. Why did Fibonacci fail the testInductiveCase test? What (if anything) did you have to do to fix it? If you did not have to change anything to fix this issue, explain why. Part 8: Debugging Tutorial In this part, you will learn about two methods for debugging - printing and IntelliJ's built-in debugger. Printing is an easy way to check the state of variables in a certain point in the program, allowing you to quickly detect problems. A debugger can help you debug your program by allowing you to "watch" your program as it executes, one line at a time, and inspect the state of variables along the way. In many cases, using a debugger can be much more powerful and convenient than littering your program with print statements. One of the most useful features of a debugger is the ability to set breakpoints in your program. When you run your program through the debugger, it will pause when it reaches a line with a breakpoint. You can inspect the current state of variables, then continue running your program normally or step through one line at a time to watch the variables change. You should reference the IntelliJ Debugger Documentation throughout this section to learn how to use the debugging tools in IntelliJ. We won't be explaining every step of using the debugger in this section, so this is a good opportunity to practice reading documentation! As you follow the instructions below, write answers to the questions below in the answers.txt file. Open Adder.java. This simple program is supposed to print the sum of two user-provided integers. Try running it a few times (or reading the source code) and you'll see that it doesn't behave as expected. You can run the program by clicking the play button next to its main method, or by running the gradle target runAdder. Locate the line int sum = computeSum(x, y); (line 32). Right between this line and the next one, write the print statement printing the variables x, y, and sum. Then, run the main method, enter 5 as the first integer and 4 as the second one. You should see that x is not the first integer you entered. Question 1: What are the values of x, y, and sum printed by your statement? Why was x not equal to the first integer entered here, and how could we fix this? Change the main method so that x is always equal to the first integer entered. Make sure to only change the main method in this step. Now we will start using the debugger. Click in the left-hand margin of the class next to the line return x - y; A red circle should appear, indicating a breakpoint. (Clicking again removes the breakpoint.) Run the program in debug mode by right-clicking on Adder.java and clicking “Debug...”. As before, enter two ints (say, 3 and 4) in the console when prompted. When your program hits the breakpoint, IntellIJ will pause the program and a debugging window will show up at the bottom of your screen. The debug perspective looks overwhelming at first, but don't worry! Look at the “Variables” pane and you'll see the names and values of all variables in the current context (which, at this breakpoint, is the computeSum method). The left panel in the frames tab shows where the program is currently paused, where the current method was called, and so on. (This is called the stack trace). Double-click on a method name to see the corresponding line in your source code. Finally, the console tab (next to “Debugger,” right above the “frames” area of the debugger) shows the console window. Question 2: What are all the names and values listed in the “Variables” panel? What does the “frames” tab list as the current method and line number? (Write down the text that was highlighted when the Debug perspective first opened.) Immediately above the “Debugger” panel, and on the left are several groups of buttons for running your program. Mouse over each one for a description. “Resume” (green arrow) causes your program to continue executing normally until it finishes or hits another breakpoint. If you want to monitor what happens shortly after the breakpoint, use “Step Into” and “Step Over” (blue arrows near the top of the debugger). “Step Over” executes the current line and pauses on the next line. “Step Into” enters any method called on the current line so you can execute that method line-by-line. (To finish the current method and jump back to the caller, use “Step Out.”) Hit “Step Over” once to execute the return statement and exit computeSum. Hit “Step Over” again to progress to the next line. Question 3: What are all the names and values listed in the “Variables” panel after each of the two step overs? Hit “Resume” to allow the program to finish executing. Being able to step through each piece of code and examine what's going on is a very powerful way to understand what your code is doing any why things may be going wrong. The IntelliJ debugger can to so much more than just what we've discussed here, so make sure to read the documentation linked above to learn more about what it can do to help you fix any problems you might have in your code. Part 9: Implementing Code with Invariants— Finder and Evaluator In the last two problems of HW1, you verified the correctness of two pieces of code by reasoning. You were given loop invariants in each question, which helped in your reasoning. In this question, you will do the opposite - given different loop invariants or pre/postconditions, you will write code that matches them. Implementing Variants of Finder Locate the Finders.java file in your repo, and open it. Here, the find1 method is the code given in HW1 Problem 8. There are also the methods find2, find3, find4 with incomplete parts. Follow the instructions given by TODO comments to complete these methods. Each version, when completed, will have the same functionality as find1 (i.e., it will produce the same outputs when given the same, valid inputs), but it will accomplish that in a slightly different way, as described by its own, particular loop invariant. You shouldn't make changes other than those denoted by the TODO comments while implementing these methods. Also, make sure to remove any TODO comments after you are done, so that it's clear no more work needs to be done in them. There are JUnit tests we wrote for this class in FinderTest, your final implementation should pass those tests as well. Since we put assert statements in your code, passing these tests would also likely mean that your code satisfies the given invariant. However, you should already have confirmed this by reasoning. Implementing Variants of Evaluator Locate the Evaluator.java file in your repo, and open it. Similar to Finder.java, the first method (evalPoly1) is the code given in HW1 Problem 9. The method evalPoly2 is incomplete, with different functionality. Make sure to read the comments to see how the intended behavior for this method is different than the first one. Then, complete this method by making changes as described in the TODO comments. When completed, the loop invariant and the postcondition given in the method should hold at those points. You shouldn't make changes other than those denoted by the TODO comments while implementing these methods. Make sure to remove any TODO comments after you are done, so that it's clear no more work needs to be done in them. There are JUnit tests we wrote for this class in EvaluatorTest, your final implementation should pass those tests as well. Unlike Finder.java, this file doesn't contain any assert statements. Therefore, your implementation is not guaranteed to satisfy the given invariant just because it passes the given tests. (Your code could have the correct behavior but be using a different invariant.) You will need to rely on reasoning alone to confirm that your code satisfies the given invariant. How to Turn In Your Homework Your answers in Part 1 should be submitted in Gradescope, as a PDF file. This should be the only part you are submitting in Gradescope. At the end of each assignment, you must refer to the Assignment Submission Handout and closely follow the steps listed to submit the rest of your assignment. Do not forget to double check your submission as described in that handout - you are responsible for any issues if your code does not run when we try to grade it. Use the tag name hw2-final for this assignment. To verify your assignment on attu, you can use any of the gradle tasks described elsewhere in this assignment: hw-setup:runHelloWorld, hw-setup:runHolaWorld, and hw-setup:runRandomHello. Don't forget to write your answers to part 7 and 8 in the provided answers.txt file in your repo. We should be able to find the following in the hw-setup/src directory of your repository: HolaWorld.java that works as described in Part 4 with no compilation errors RandomHello.java that prints out one of five random messages when its main method is executed Fibonacci.java that passes the three tests in FibonacciTest.java (Note that you should not edit FibonacciTest.java to accomplish this task.) Finder.java and Evaluator.java, where the implemented parts satisfy the given invariants and/or assertions. These classes should also pass the tests written for them, and you should not edit any test files to accomplish this task.
