Recitation 9 for CS160

Recitation R9 - File Input & Output
Summer 2016

CS160: Foundations in Programming

Preview

The purpose of this lab is to:

Learn how to read a file using Scanner.
Learn how to write a file using PrintWriter.
Create a method that will read in from a file and parse a unique file format.
Create a method that will write out to a file.
Complete the Hackerrank exercises dealing with Advanced Scanner Techniques.

Phase 0: Setting Up

Make a new project and class in Eclipse called R9, with a main method.
Run the program once so that eclipse is pointing at your R9 project.
Set up the Run Configuration so that R9 has the program arguments:

input.txt output.txt

Create and complete the following 3 classes inside your P9 project:

Phase 1: Starting R9

In your R9 class, declare the following 3 instance variables:


    private Rectangle [] rArray;
    private Triangle [] tArray;
    private Circle [] cArray;

Copy the following getter methods into your class for testing purposes:


    public Rectangle[] getRectangles(){
	return rArray;
    }

    public Triangle[] getTriangles(){
	return tArray;
    }

    public Circle[] getCircles(){
	return cArray;
    }

Create two methods with the following signatures:


    public void readFile( String inputFile ){ }

    public void writeFile( String outputFile ){ }

Within the main method:

Create an object of type R9 named r9.
Use your R9 object to call the readFile method with the first command line argument (args[0]).
Use your R9 object to call the writeFile method with the second command line argument (args[1]).

Phase 2: Completing the readFile method

First of all, you're going to have a choice. Each of the following input files is formatted a little bit differently. Depending on how the file is formatted, you will write the calls to Scanner in your readFile method differently. Choose and save one of the following files into your R9 project:

Each file will have the following componenets:

What size the 3 instance arrays should be.
A way to differentiate and information about each object (height, width, radius, base, etc)

Implement the readFile method to:

Open the input file of your choice
Parse the contents of the input files so that it populates all three instance arrays.
Here is an example to get you started.

To test this and make sure that your readFile method is working correctly, after the call to readFile in your main method put the following code in:

System.out.println(Arrays.toString(r9.rArray));
System.out.println(Arrays.toString(r9.cArray));
System.out.println(Arrays.toString(r9.tArray));

This should print out the contents of each of your arrays.

Phase 3: Completing the writeFile method

Now that we have populated the arrays using the readFile method, it's time to write our results out to a file!

Open up the file using the PrintWriter class.
Loop through your instance variables in the following order: rArray, cArray, tArray.

Write each object inside the arrays out to file, one per line, with the element number prepended to the front. An Example would be:

1: Rectangle, (Width: 4.00, Length: 2.20), Area: 8.80
2: Circle, (Radius: 8.60), Area:  232.35
3: Circle, (Radius: 7.90), Area:  196.07
4: Circle, (Radius: 2.10), Area:  13.85
5: Circle, (Radius: 6.18), Area:  119.98
6: Triangle, (Height: 5.00, Base: 6.00), Area: 15.00
7: Triangle, (Height: 3.30, Base: 8.20), Area: 13.53
8: Triangle, (Height: 5.50, Base: 10.10), Area: 27.78

Once you are finished:
- Run your program.
- Refresh your R9 project in eclipse (output.txt should appear under input.txt).
- Open output.txt and make sure your output looks correct.

Phase 4: Submitting your Assignment

Since there are multiple files associated with this recitation, we need a good way to turn them in! This is where JAR files come into play. It's a nice way of packaging all of your code, so that you only have to submit one file.

Right click on your R9 project and select Export
Expand Java, highlight the JAR file option, and then select Next. Your screen should look like this.
Make sure that Export Java source files and resources is selected
In the upper left hand corner, uncheck everything except your input.txt
Under Select the export destination: Select Browse... I like to put my JAR files in the project level of my directory. But so long as you can find it, you can put the JAR file anywhere. Make sure your JAR File Specification matches this image before selecting Finish.

HackerRank

Once your are finished go here and complete the Advanced Scanner problems on Hackerrank.

Submit R9.tar to Checkin and Complete the Hackerrank problems.

Recitation R9 - File Input & Output Summer 2016