debugging exercise java

Right-click on it and select Debug As Java Application. Help with a quick Java code debugging exercise. Debug E9. In each case, determine and fix the problem, remove all syntax and coding errors, and run the program to ensure it works properly. Just be aware that you could also be introducing problematic behavior when evaluating expressions. Given crewStatus and computerStatus, should launchReady be true or false after this check? Learn more. Essentially, threads should be used to run independent processes but if threads work on the same process there is no guarantee of execution of statements in different threads in a particular order. To investigate further, try to complete the following debugging steps: Although breakpoints allow us a chance to peek inside running code, many times when debugging youll find that youre missing a piece of information not provided by the current code - perhaps youd like to call a utility method, or construct a new object temporarily. Double-sided tape maybe? In the second for loop Java is constantly in the process of reclaiming objects that are no longer in use (garbage collection). In this article, we are going to see what makes debugging stand out of the queue and how it is different from software testing. To launch an application into the market, it is very necessary to cross-check it multiple times so as to deliver an error-free product. They provide a way to instruct Java to stop code execution when a certain line of code is encountered, providing a chance to explore actively running code. We will be discussing the following topics: In the development process of any software, the software program is religiously tested, troubleshot, and maintained for the sake of delivering bug-free products. They provide a way to instruct Java to stop code execution when a certain line of code is encountered, providing a chance to explore actively running code. Exercise 8. start Declarations num firstTest num secondTest num, Fix the code. How to make chocolate safe for Keidran? The test gives candidates 30 minutes to read through requirements and fix a partially working script. To identify subtle problems, like memory leaks, it helps to learn how to use external tools - like. One solution a programmer may think of is to keep track of time taken by comparing values returned by System.currentTimeMillis, but this method does not scale up for large program and requires modifications to the code. It is much more efficient and useful to use a profiler to monitor time spent in methods - which is part of the jvisualvm troubleshooting tool. All of these operations are Java expressions - statements in Java syntax resolving to a single value (essentially - one line of code). Or you can switch to JvisualVM and see how much time is taken by each of function in real time. I need to fix a code that is meant to determine how much money you'd have each day if you doubled it everyday after starting with a penny. Even if you can't contribute a fix, if you went through the effort of debugging - at the very least you should identify the problem, steps you took to debug, and potential fix(es) via a bug report so that your effort is not lost. Whatever follows that entry is at the top of the stack, and thus what was being processed on that thread when you took the stack trace. To acquire the heap dump: So now we know what's taking up all of our memory - but we don't actually know why. This repository has been archived by the owner before Nov 9, 2022. clues about what is going wrong. It also allows much of the process to be automated. First set a breakpoint on the line after the everythingIsOK assignment: >If the broken object appears later the second time, your breakpoint will hit but the current object will likely be fine. All those errors and bugs are discarded regularly, so we can conclude that debugging is nothing but a process of eradicating or fixing the errors contained in a software program. All of these operations are Java expressions - statements in Java syntax resolving to a single value (essentially - one line of code). In each case, determine and fix the 4public static void main(String args[]) problem, remove all syntax and coding errors, and run the program to ensure it works properly. You should see it print array names for a while, and then eventually hit an OutOfMemoryError. I've played with the code so much that I don't remember any specific problems that I've had. Are you sure you want to create this branch? All rights reserved. Java uses exceptions to handle errors and other exceptional events. launch. What was suspicious about the object at that index? To investigate further, close ImageJ (if its running) and launch it again from the command line, e.g. modified the instance and add pages and area because no default constructor in DebugPhoneBook. Course Hero is not sponsored or endorsed by any college or university. Debugging assist the developer in reducing impractical and disrupting information. in the first if/else block got changed in the second if/else Next we need to connect Eclipse to the running ImageJ instance: At this point ImageJ and Eclipse should be communicating. *; Answer: ``` Like the previous exercise, we have a stack trace to start from: Try setting a breakpoint on the conditional line: Since we are only interested in the processElementAtIndex method when a problem actually occurs, lets try something different: At this point, we know there is a problem accessing the 99999th element of the list, but the variables window doesnt tell us exactly what the problem is. https://www.cengage.com/c/java-programming-9e-farrell/9781337397070 This time our console output looks a bit different: In addition to the exception stack trace, the program itself appears to have found an invalid object, causing the processing to go unfinished. In case of multithreaded programming, set breakpoints to stop the virtual machine at the breakpoint to freeze the state of all threads. Build and share projects in your browser. Instead, lets use expressions. They are limited. Identifying the breaking change gives us more information to use in our diagnosis (and in some cases, can be fixed with a simple git revert]). You should get an exception: In order to connect Eclipse to ImageJ, we need to close our running instance and launch ImageJ from the command line, which allows us to set the debug flag, e.g. For this exercise we have some additional information: this class used to run successfully, and a tag was made at that point. The goal of these exercises is not to solve the problems, but to build up your toolbox of troubleshooting techniques and develop your intuition for when to apply each technique. Note that it works fine, Now set a breakpoint in the getName method of either the Even or Odd LonelyRunnable, Set the breakpoints property to Suspend thread. To use the bisect tool we just need to know two commits: one where the test worked, and one where the test failed. They are slow. Both functions are called one after the other for two minutes. Our goal is to find which function is slower than the other. While bisecting, the whole local repository is in a special "BISECTING" mode - so that git can remember your answers for each commit. While debugging, you are in full control of the things. Arrr! Insert a breakpoint on the while statement in main method; Launch JvisualVM. When you hit a breakpoint, make sure you resume the VM and not just the thread. So a natural question that follows is - once weve successfully identified the cause of an issue (or at least narrowed things down), what are the next steps to take? That's the easiest way to learn. Hint: raw stack dumps like this are not the easiest to read. Are the models of infinitesimal analysis (philosophically) circular? if our program crashes without warning, or becomes unresponsive), Analyze a heap dump for potential problems, From the list of local applications, right-click on, The "Summary" view is open by default; switch to the "Classes" view of the heap dump, With the heap dump selected in the Applications list of, Back in Eclipse, open the "Memory Analysis" perspective (, Filter the classes of the histogram based on the problematic class you identified in. Exercise 11. Help your friend find all the bugs in the program! If the code is excessively complex, or the problem subtle, it may not be practical to try and step through code execution - you may not even be sure where to start. Compile and run it to make sure it is correct and then complete each of the following problems. The act of debugging can change the way our code executes. Transcribed image text: Debugging Exercise 8-1 Instructions DebugEight1.java 1 import java.util. This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository. Because this project is intended to help new developers practice troubleshooting skills, you may find these examples contrived - indeed, they are. It is now read-only. Right now, we're learning about methods, returns, classes, objects, etc. Strange fan/light switch wiring - what in the world am I looking at. to print a countdown and "Liftoff!" When debugging we're trying to identify why a program isn't behaving as expected. These exercises have syntactical errors and functional mistakes (the latter of which the author somewhat confusingly calls logical errors). So looking back at the stack trace we got, we can see what went wrong (tried to use a null object) and where it happened (the line number at the top of the stack), but we don't know why the object was null at that point - which would be the actual root cause of the exception. to use Codespaces. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. I'm doing a debugging exercise for my java class. Developing codes may often involve using multiple threads instead of sequential execution of statements. Although plugin developers typically set up tests to run their plugin within ImageJ, it is impossible to test all possible runtime environments: users could have a variety of update sites enabled, custom plugins installed, etc and each modification is an opportunity for dependency skew and clashes with your plugin. Fortunately, breakpoints have an optional "Conditional" flag - where we can enter any Java statement that resolves to a boolean value. Instead, let's use expressions. So the first step in fixing performance is identifying the location of the slowdown. Connect and share knowledge within a single location that is structured and easy to search. Did we mention your crew are space pirates? Each process throws up an error if the other process introduces a delay more than one second. Instead of making these changes in your program's code and recompiling, in Debug mode we can dynamically evaluate any expression on-demand, without changing the source. If at any time you need to revert changes to the imagej-troubleshooting repository, you can always do so via the command: Breakpoints are a fundamental tool of debugging. Debugging Exercise 8-1 Instructions DebugEight1.java 1 import java.util. Exercise 2. However, there are critical drawbacks to trying to debug via print statement: Learning to use debugging tools is, understandably, a burden: its one more thing to learn as a developer. Right-click the row for the problematic class and select the Merge Shorted Paths to GC Roots > exclude weak/soft references option. If you have complete knowledge and understanding of the code there isnt really a need for troubleshooting: it is trivial to see why something is behaving incorrectly. *; 2 public class DebugEight1 The files provided in the code editor to the right contain l syntax and/or logic errors. To find what tags are available, on the command line we can run: The purpose of the bisect tool is to search our commit history to find the breaking commit. /* package whatever; // don't place package name! So the resulting stack trace may be misleading. Run the class in Eclipse and you should see some simple output in the console: Next, we want to run this plugin in ImageJ and see what happens: Note that the menu path of the plugin is specified in the class's annotation: So, you can now run the E4 - Print ConsoleService command either via the menus or command finder. Dont be intimidated by them embrace them. All running Java applications are shown in the in Applications Tab (left margin) of JvisualVM. If you ever make a mistake (marking a commit incorrectly) you can abort the process via git bisect reset. Try it out: Were you able to get the breakpoint to stop in the loop only when a problem is encountered?