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CS1331 Homework 03 Solution
Authors: Jacob, Angela, Ishuma, Ariel, Nicolas
Problem Description
Propulsion Laboratory in Pasadena, California, home to the facilities for the Deep Space Network in the United States. Since you’re just getting started, we have a deeply exciting assignment for you: converting old satellite classification data from its original format into something more readable by modern software, so that the American people can peruse our satellite catalog from a website your fellow interns are writing. You’ll be responsible for reading the traditional two-line element set (TLE) format from plain text files, using polymorphic methods on the objects representing the satellites, and then saving the data to a new file, in an easier to read format. For those who are interested, an explanation of the TLE format can be found in the Appendix of this PDF. Good luck: the people of our nation are counting on you.
Solution Description
In this assignment you will get practice with file I.O., polymorphism, and exception handling. You will be provided a folder named satellite_data with several files in it. This is the test data set you will use to verify your code works. In addition, you will be provided with a java class called SatelliteTLEParser, which we are providing to you to handle the messier work of reading the TLE format. You will write your program in a Java class called
SatelliteDataConverter and it should use Java’s built in File I/O classes and methods to iterate through the folder, open each file, load the data within, pass the data to the parser method, and then write that data out to a new file. Your code should be able to handle any valid data we give it – do not hardcode to the provided test data.
Satellite Classes
In addition, you will write three Java classes to represent the satellite objects: Satellite,
ClassifiedSatellite, and GeostationarySatellite. Since classified and geostationary satellites are satellites, your class structure should reflect that “is-a” relationship.
Satellite.java
• Variables
All three satellite classes should have the following fields, either explicitly or via inheritance:
o String name o int catalogNumber o int launchYear o int launchDay o double inclination o double meanMotion
All fields should be private.
• Constructor o Include a constructor that takes in name, catalogNumber, launchYear, launchDay, inclination, and meanMotion in this exact order.
• Methods
o orbitTime()
The “mean motion” of a satellite is defined as the number of orbits around earth per day. This mathematical definition is useful for astronomers and rocket scientists, but we’d prefer to offer a more easily digestible number: the number of minutes it takes for the satellite to complete one orbit. Since the mean motion is the number of orbits per day, we can calculate the orbit time in minutes with the following formula:
time = (24 * 60) / meanMotion
This method should return the result of this calculation as a double.
o toString()
This method should return a string with the following format with a newline at the end:
“{name}: #{catalogNumber}. Launched on day {launchDay} of {launchYear}. Inclination: {inclination} degrees.
{meanMotion} orbits per day - {orbitTime()} minutes per orbit.”
The curly braces {} denote values that should be replaced with the corresponding variable(s), do not include the curly braces in your output.
Do not round any of the floating-point values in your output.
o encodeCSV()
This method should also return a string with a newline at the end, but it should be in a comma-separated format, as shown below:
“{name},{catalogNumber},{launchYear},{launchDay},{inclinatio n},{meanMotion},{orbitTime()}”
The curly braces {} denote values that should be replaced with the corresponding variable(s), do not include the curly braces in your output.
Do not round any of the floating-point values in your output.
ClassifiedSatellite.java
Under the TLE format, there are three supported levels of classification: unclassified, classified, and secret. To keep things simple, you will create an additional Java class, ClassifiedSatellite, to handle both classified and secret satellites, which will extend Satellite. This class will support the same functions as the parent class but will require authentication by the user to invoke any of its methods that output information (toString() and encodeCSV()).
• Include a constructor that takes in name, catalogNumber, launchYear, launchDay, inclination, and meanMotion in this exact order.
o Ensure that you call the constructor located in the Satellite class from this constructor to maximize code reuse
• To facilitate authentication for toString() and encodeCSV(), you should read in user input, and check if the input matches the password.
o Prompt the user for the password by printing “Password:” to the terminal with a newline at the end.
o If the user enters the correct password, return the normal value for the method called.
o If the user does not enter the correct password, you should not return the normal value, but rather the String “INCORRECT PASSWORD”.
o The password you should check against is “f8ee89496da476b3849f4de45a4528b4”.
• Hint: we strongly recommend writing a helper method to handle the password check.
• Note: the mainframe on which this code will be running has dangerously limited storage capacity, and so any duplication of code is a hindrance to the mission. For full credit, you should reuse code whenever possible – using the parent methods from Satellite is a requirement.
GeostationarySatellite.java
You’ll also write a third class: GeostationarySatellite, which will also extend Satellite. Geostationary satellites are those which orbit perfectly in sync with the rotation of the Earth, meaning that they remain over the same location in perpetuity.
• Include a constructor that takes in name, catalogNumber, launchYear, launchDay, and inclination in this exact order.
o Since they all orbit once per day, every GeostationarySatellite should have a meanMotion of 1.0. o Ensure that you call the constructor located in the Satellite class from this constructor to maximize code reuse.
SatelliteDataConverter.java
This class will be responsible for the execution of your program. Use methods from existing Java File I/O libraries to help you—do not reinvent the wheel. If you aren’t sure where to start, look at the Java API to find methods that might be useful to you. Additionally, remember you must make necessary imports and handle any associated Exceptions when working with File I/O in Java.
• Methods o createSatelliteArray()
Private static helper method that takes in the File object representing the satellite_data folder.
This method should determine how many files belong to the folder – remember, one satellite per file – and pass each file’s data to the
SatelliteTLEParser.parseData() method, which expects the entire contents of one file as a String.
Note: SatelliteTLEParser.parseData() expects the passed-in String to include the newlines from the original file. As such, you must take care to preserve the newline characters when you read in each file.
SatelliteTLEParser.parseData() will return the appropriate Satellite object, which you should store in an array of Satellite objects that you will return.
Your code won’t know (and doesn’t need to know) which kind of satellite object was loaded – polymorphism in action!
o main()
Your program should expect the first command line argument passed to it to be the relative path to the folder containing the satellite data and should then create a File object using this command line argument.
Note: When you are running your program, you will need to pass the path to the "satellite_data" folder as a command line argument. If you are running your program from the terminal, simply run "java
SatelliteDataConverter {relative path to
satellite_data}”. If you are running your program from IntelliJ, please see this guide for instructions on how to add command line arguments.
Your program should then open each file within the folder and parse through its data to create a Satellite object for each file.
Utilize the createSatelliteArray() helper method to help you.
After all the text files have been loaded into the program, decoded, and the appropriate satellite objects have been stored in an array, your program should open a new file named “satellite_output.csv”. It should fill this file with the string from each satellite object’s encodeCSV() method, with a new line between each satellite.
Hint: Iterating over the array returned from createSatelliteArray() is the simplest way to do this.
Whenever working with File objects, be prepared to handle checked exceptions, particularly FileNotFoundExceptions and IOExceptions. Use try/catch blocks to handle any potential errors. If you encounter an exception, you should print out the exception’s message field followed by a newline.
Your efforts will enhance our nation’s scientific and defense capabilities, and we thank you!
Hints
• The format of your output must match character-for-character. This is because your output, if done correctly, will be able to be viewed in any spreadsheet program, or by any spreadsheet-processing code. (Try this out in your tests!)
• If you can find out what text I used to generate the test password, I’ll nominate you for a Turing Award. Hint: Google “md5 hash”.
Appendix
ISS (ZARYA)
1 25544U 98067A 08264.51782528 -.00002182 00000-0 -11606-4 0 2927
2 25544 51.6416 247.4627 0006703 130.5360 325.0288 15.72125391563537
• Line 1 o ISS (ZARYA) is the satellite name
• Line 2 o The first character will always be 1
o 25544U is the combination of the catalogNumber, which will always be 5 characters, and the classification level (U = Unclassified, C = Classified, S = Secret)
o 98067A is the international designator
o 08264.51782528 contains the epoch launchYear (08) and the epoch launchDay (the rest of the token).
o The rest of the information in the second line is not needed for the Satellite class
• Line 3
o The first character will always be 2 o 25544 is the catalogNumber o 51.6416 is the inclination
o The fourth, fifth, sixth, and seventh tokens in the third line are not needed for the Satellite class
o 15.72125391 is the meanMotion and the rest of the eighth token is not needed for the Satellite class
Clarifications and Example Output
Allowed Imports
You will need to import many Java classes to complete this assignment. At minimum, java.io.File,
java.io.FileNotFoundException, java.io.PrintWriter , java.util.Scanner, and/or
java.io.FileReader, and will likely prove useful. However, you can use any class from the standard library you choose.
Feature Restrictions
There are a few features and methods in Java that overly simplify the concepts we are trying to teach or break our auto grader. For that reason, do not use any of the following in your final submission:
• var (the reserved keyword)
• System.exit
Checkstyle and Javadocs
You must run Checkstyle on your submission. The Checkstyle cap for this assignment is 9 points. If you don't have
Checkstyle yet, download it from Canvas -> Modules -> Checkstyle Resources (Section B & C) or General Information (Section D) -> checkstyle-8.28.jar. Place it in the same folder as the files you want Checkstyled. Run checkstyle on your code like so:
$ java -jar checkstyle-8.28.jar yourFileName.java
Starting audit...
Audit done.
The message above means there were no Checkstyle errors. If you had any errors, they would show up above this message, and the number at the end would be the points we would take off (limited by the Checkstyle cap mentioned above). The Java source files we provide contain no Checkstyle errors. In future homeworks we will be increasing this cap, so get into the habit of fixing these style errors early!
Additionally, you must Javadoc your code.
Run the following to only check your Javadocs:
$ java -jar checkstyle-8.28.jar -j yourFileName.java
Run the following to check both Javadocs and Checkstyle:
$ java -jar checkstyle-8.28.jar -a yourFileName.java
For additional help with Checkstyle see the CS 1331 Style Guide.
Collaboration
No collaboration is allowed on this assignment. See syllabus for more details.
Turn-In Procedure
Submission
To submit, upload the files listed below to the corresponding assignment on Gradescope:
• Satellite.java
• ClassifiedSatellite.java
• GeostationarySatellite.java
• SatelliteDataConverter.java
Please only submit the individual files—do not put them into a package or you will risk getting a zero on the assignment. Make sure you see the message stating "HW03 submitted successfully". From this point, Gradescope will run a basic autograder on your submission as discussed in the next section.
Gradescope Autograder
For each submission, you will be able to see the results of a few basic test cases on your code. Each test typically corresponds to a rubric item, and the score returned represents the performance of your code on those rubric items only. If you fail a test, you can look at the output to determine what went wrong and resubmit once you have fixed the issue.
The Gradescope tests serve two main purposes:
• Prevent upload mistakes (e.g. non-compiling code)
• Provide basic formatting and usage validation
• Non-compiling files will receive a 0 for all associated rubric items
• Do not submit .class files
• Test your code in addition to the basic checks on Gradescope
• Run Checkstyle on your code to avoid losing points
• Submit every file each time you resubmit
• Read the "Allowed Imports" and "Feature Restrictions" to avoid losing points
• Check on Piazza for a note containing all official clarifications
Problem Description
Propulsion Laboratory in Pasadena, California, home to the facilities for the Deep Space Network in the United States. Since you’re just getting started, we have a deeply exciting assignment for you: converting old satellite classification data from its original format into something more readable by modern software, so that the American people can peruse our satellite catalog from a website your fellow interns are writing. You’ll be responsible for reading the traditional two-line element set (TLE) format from plain text files, using polymorphic methods on the objects representing the satellites, and then saving the data to a new file, in an easier to read format. For those who are interested, an explanation of the TLE format can be found in the Appendix of this PDF. Good luck: the people of our nation are counting on you.
Solution Description
In this assignment you will get practice with file I.O., polymorphism, and exception handling. You will be provided a folder named satellite_data with several files in it. This is the test data set you will use to verify your code works. In addition, you will be provided with a java class called SatelliteTLEParser, which we are providing to you to handle the messier work of reading the TLE format. You will write your program in a Java class called
SatelliteDataConverter and it should use Java’s built in File I/O classes and methods to iterate through the folder, open each file, load the data within, pass the data to the parser method, and then write that data out to a new file. Your code should be able to handle any valid data we give it – do not hardcode to the provided test data.
Satellite Classes
In addition, you will write three Java classes to represent the satellite objects: Satellite,
ClassifiedSatellite, and GeostationarySatellite. Since classified and geostationary satellites are satellites, your class structure should reflect that “is-a” relationship.
Satellite.java
• Variables
All three satellite classes should have the following fields, either explicitly or via inheritance:
o String name o int catalogNumber o int launchYear o int launchDay o double inclination o double meanMotion
All fields should be private.
• Constructor o Include a constructor that takes in name, catalogNumber, launchYear, launchDay, inclination, and meanMotion in this exact order.
• Methods
o orbitTime()
The “mean motion” of a satellite is defined as the number of orbits around earth per day. This mathematical definition is useful for astronomers and rocket scientists, but we’d prefer to offer a more easily digestible number: the number of minutes it takes for the satellite to complete one orbit. Since the mean motion is the number of orbits per day, we can calculate the orbit time in minutes with the following formula:
time = (24 * 60) / meanMotion
This method should return the result of this calculation as a double.
o toString()
This method should return a string with the following format with a newline at the end:
“{name}: #{catalogNumber}. Launched on day {launchDay} of {launchYear}. Inclination: {inclination} degrees.
{meanMotion} orbits per day - {orbitTime()} minutes per orbit.”
The curly braces {} denote values that should be replaced with the corresponding variable(s), do not include the curly braces in your output.
Do not round any of the floating-point values in your output.
o encodeCSV()
This method should also return a string with a newline at the end, but it should be in a comma-separated format, as shown below:
“{name},{catalogNumber},{launchYear},{launchDay},{inclinatio n},{meanMotion},{orbitTime()}”
The curly braces {} denote values that should be replaced with the corresponding variable(s), do not include the curly braces in your output.
Do not round any of the floating-point values in your output.
ClassifiedSatellite.java
Under the TLE format, there are three supported levels of classification: unclassified, classified, and secret. To keep things simple, you will create an additional Java class, ClassifiedSatellite, to handle both classified and secret satellites, which will extend Satellite. This class will support the same functions as the parent class but will require authentication by the user to invoke any of its methods that output information (toString() and encodeCSV()).
• Include a constructor that takes in name, catalogNumber, launchYear, launchDay, inclination, and meanMotion in this exact order.
o Ensure that you call the constructor located in the Satellite class from this constructor to maximize code reuse
• To facilitate authentication for toString() and encodeCSV(), you should read in user input, and check if the input matches the password.
o Prompt the user for the password by printing “Password:” to the terminal with a newline at the end.
o If the user enters the correct password, return the normal value for the method called.
o If the user does not enter the correct password, you should not return the normal value, but rather the String “INCORRECT PASSWORD”.
o The password you should check against is “f8ee89496da476b3849f4de45a4528b4”.
• Hint: we strongly recommend writing a helper method to handle the password check.
• Note: the mainframe on which this code will be running has dangerously limited storage capacity, and so any duplication of code is a hindrance to the mission. For full credit, you should reuse code whenever possible – using the parent methods from Satellite is a requirement.
GeostationarySatellite.java
You’ll also write a third class: GeostationarySatellite, which will also extend Satellite. Geostationary satellites are those which orbit perfectly in sync with the rotation of the Earth, meaning that they remain over the same location in perpetuity.
• Include a constructor that takes in name, catalogNumber, launchYear, launchDay, and inclination in this exact order.
o Since they all orbit once per day, every GeostationarySatellite should have a meanMotion of 1.0. o Ensure that you call the constructor located in the Satellite class from this constructor to maximize code reuse.
SatelliteDataConverter.java
This class will be responsible for the execution of your program. Use methods from existing Java File I/O libraries to help you—do not reinvent the wheel. If you aren’t sure where to start, look at the Java API to find methods that might be useful to you. Additionally, remember you must make necessary imports and handle any associated Exceptions when working with File I/O in Java.
• Methods o createSatelliteArray()
Private static helper method that takes in the File object representing the satellite_data folder.
This method should determine how many files belong to the folder – remember, one satellite per file – and pass each file’s data to the
SatelliteTLEParser.parseData() method, which expects the entire contents of one file as a String.
Note: SatelliteTLEParser.parseData() expects the passed-in String to include the newlines from the original file. As such, you must take care to preserve the newline characters when you read in each file.
SatelliteTLEParser.parseData() will return the appropriate Satellite object, which you should store in an array of Satellite objects that you will return.
Your code won’t know (and doesn’t need to know) which kind of satellite object was loaded – polymorphism in action!
o main()
Your program should expect the first command line argument passed to it to be the relative path to the folder containing the satellite data and should then create a File object using this command line argument.
Note: When you are running your program, you will need to pass the path to the "satellite_data" folder as a command line argument. If you are running your program from the terminal, simply run "java
SatelliteDataConverter {relative path to
satellite_data}”. If you are running your program from IntelliJ, please see this guide for instructions on how to add command line arguments.
Your program should then open each file within the folder and parse through its data to create a Satellite object for each file.
Utilize the createSatelliteArray() helper method to help you.
After all the text files have been loaded into the program, decoded, and the appropriate satellite objects have been stored in an array, your program should open a new file named “satellite_output.csv”. It should fill this file with the string from each satellite object’s encodeCSV() method, with a new line between each satellite.
Hint: Iterating over the array returned from createSatelliteArray() is the simplest way to do this.
Whenever working with File objects, be prepared to handle checked exceptions, particularly FileNotFoundExceptions and IOExceptions. Use try/catch blocks to handle any potential errors. If you encounter an exception, you should print out the exception’s message field followed by a newline.
Your efforts will enhance our nation’s scientific and defense capabilities, and we thank you!
Hints
• The format of your output must match character-for-character. This is because your output, if done correctly, will be able to be viewed in any spreadsheet program, or by any spreadsheet-processing code. (Try this out in your tests!)
• If you can find out what text I used to generate the test password, I’ll nominate you for a Turing Award. Hint: Google “md5 hash”.
Appendix
ISS (ZARYA)
1 25544U 98067A 08264.51782528 -.00002182 00000-0 -11606-4 0 2927
2 25544 51.6416 247.4627 0006703 130.5360 325.0288 15.72125391563537
• Line 1 o ISS (ZARYA) is the satellite name
• Line 2 o The first character will always be 1
o 25544U is the combination of the catalogNumber, which will always be 5 characters, and the classification level (U = Unclassified, C = Classified, S = Secret)
o 98067A is the international designator
o 08264.51782528 contains the epoch launchYear (08) and the epoch launchDay (the rest of the token).
o The rest of the information in the second line is not needed for the Satellite class
• Line 3
o The first character will always be 2 o 25544 is the catalogNumber o 51.6416 is the inclination
o The fourth, fifth, sixth, and seventh tokens in the third line are not needed for the Satellite class
o 15.72125391 is the meanMotion and the rest of the eighth token is not needed for the Satellite class
Clarifications and Example Output
Allowed Imports
You will need to import many Java classes to complete this assignment. At minimum, java.io.File,
java.io.FileNotFoundException, java.io.PrintWriter , java.util.Scanner, and/or
java.io.FileReader, and will likely prove useful. However, you can use any class from the standard library you choose.
Feature Restrictions
There are a few features and methods in Java that overly simplify the concepts we are trying to teach or break our auto grader. For that reason, do not use any of the following in your final submission:
• var (the reserved keyword)
• System.exit
Checkstyle and Javadocs
You must run Checkstyle on your submission. The Checkstyle cap for this assignment is 9 points. If you don't have
Checkstyle yet, download it from Canvas -> Modules -> Checkstyle Resources (Section B & C) or General Information (Section D) -> checkstyle-8.28.jar. Place it in the same folder as the files you want Checkstyled. Run checkstyle on your code like so:
$ java -jar checkstyle-8.28.jar yourFileName.java
Starting audit...
Audit done.
The message above means there were no Checkstyle errors. If you had any errors, they would show up above this message, and the number at the end would be the points we would take off (limited by the Checkstyle cap mentioned above). The Java source files we provide contain no Checkstyle errors. In future homeworks we will be increasing this cap, so get into the habit of fixing these style errors early!
Additionally, you must Javadoc your code.
Run the following to only check your Javadocs:
$ java -jar checkstyle-8.28.jar -j yourFileName.java
Run the following to check both Javadocs and Checkstyle:
$ java -jar checkstyle-8.28.jar -a yourFileName.java
For additional help with Checkstyle see the CS 1331 Style Guide.
Collaboration
No collaboration is allowed on this assignment. See syllabus for more details.
Turn-In Procedure
Submission
To submit, upload the files listed below to the corresponding assignment on Gradescope:
• Satellite.java
• ClassifiedSatellite.java
• GeostationarySatellite.java
• SatelliteDataConverter.java
Please only submit the individual files—do not put them into a package or you will risk getting a zero on the assignment. Make sure you see the message stating "HW03 submitted successfully". From this point, Gradescope will run a basic autograder on your submission as discussed in the next section.
Gradescope Autograder
For each submission, you will be able to see the results of a few basic test cases on your code. Each test typically corresponds to a rubric item, and the score returned represents the performance of your code on those rubric items only. If you fail a test, you can look at the output to determine what went wrong and resubmit once you have fixed the issue.
The Gradescope tests serve two main purposes:
• Prevent upload mistakes (e.g. non-compiling code)
• Provide basic formatting and usage validation
• Non-compiling files will receive a 0 for all associated rubric items
• Do not submit .class files
• Test your code in addition to the basic checks on Gradescope
• Run Checkstyle on your code to avoid losing points
• Submit every file each time you resubmit
• Read the "Allowed Imports" and "Feature Restrictions" to avoid losing points
• Check on Piazza for a note containing all official clarifications
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