Lab 09 - File Input

This lab will focus upon String Manipulation and File Input. If you need to brush up on these topics, a small section will be at the lower portion of this document to catch you up on today's topics!

When downloading this program for your use, make sure to download or pull from the GitHub to ensure that you have the correct file hierarchy/format needed for this program. For instance, your files should look like this:

If this is not the configuration of your files you WILL run into problems. (Don't mind the colors, they are for GitHub version control.)

For ease of access, here is the javadoc.

Pre-Step: Walkthrough

Before beginning this assignment, it is highly recommended to start in ShippingMain's main function and try to walkthrough the program. The Product and ShippingManifest classes are provided as containers for data, they also have their own methods so it will help to check out those classes.

Step 1: Compilation

As with all Tuesday labs, you should try to compile and run the program. You can try this by running the ShippingMain.java file, you will see that some gibberish is printed because we are missing some code in two methods in ShippingMain.java. After your efforts, this gibberish should be readable and the App should receive commands and use them!

Step 2: Self-Explanation

There will be two methods within the ShippingMain class for you to self explain and complete. The javadoc will help you formulate and create your self-explanation for these methods. These methods are difficult to explain and create, so it may be of some use to pseudocode along side your actual self-explanation.

Whether you believe your self-explanation is correct or not, try to implement the method based upon it. If you see any changes that are needed apply them to both your self-explanation and code.

Step 3: Implementation

This step is just to move on to actually implementing your code within your proposed self-explanation. As previously stated, try to implement based off of your explanation, and if you must change something from the explanation, change that too!

Step 4: Testing

Once you have completed implementing, try to test your createProduct(Scanner) method using the provided ShippingTester file. There is only one method provided to test this method. If you are so inclined to create more tests to verify it works properly, go ahead it is encouraged! For testing the next method you implemented, go(Scanner, ShippingManifest), this is up to you to test manually. So try to run through your program a couple of times before turning it in.

Step 5: Turning In

Make sure to submit your ShippingMain.java file to zyBooks and then show your TA your self-explanation and pseudo-code if you did it. Online students do not have the option to submit their self-explanations but they are still highly recommended to complete to better your understanding of the code.

Additional Information

String Manipulation

Strings are incredibly useful for storing multiple characters, they also have some methods that allow us to manipulate and query those characters.

String.substring(beginIndex, endIndex)

is an incredibly handy method that allows us to slice up our String objects into more useful bits. An odd trait of substring() is that the first indicates is inclusive, meaning when we slice our String, we include that index. The endIndex is exclusive and will not include that index in our slice. Also, endIndex is optional, and if it is not included, the slice will span from beginIndex to the length of your String object.

For example:

String pokemon = "Giratina";
String name = pokemon.substring(4);

System.out.println(pokemon); //Prints "Giratina"
System.out.println(name); //Prints "tina"

String song = "Duckworth";
String animal = song.substring(0, song.indexOf("w"));

System.out.println(song); //Prints "Duckworth"
System.out.println(animal); //Prints "Duck"

String Querying

Finding characters, testing if Strings are equal, or testing what a String starts with a useful interactions that we can already do with Strings.

String.contains(String) is a useful function that returns a boolean when the first String contains the second String.

String bk = "Royale With Cheese";
String cheese = "Cheese";

System.out.println(bk.contains(cheese)); //Prints true

String.startsWith(String) is a method returns a boolean, true if the first String contains, at the the beginning, the second String.

String country = "Portugal";

System.out.println(country.startsWith("Port")); //Prints true

File Input

File Input is quite a large subject to go over in a lab README, so look at your notes/lecture notes to get the full understanding, but I will provide some helpful methods.

File objects can be needed as a parameter for Scanner objects to read the selected file, like so: (Assume we have access to this file)

File newFile = new File("testfile.txt") //Parameter is the file path.
Scanner scnr = new scnr(newFile);

String firstFileLine = scnr.nextLine();

Once you have a Scanner that is associated with your file, you can use methods like Scanner.nextLine() and Scanner.next() to actually read from your selected file.

If we had this file name test.txt:

Hi there
Nice to meet ya!

And this snippet will have an associated Scanner read the file:

String firstLine = scnr.nextLine() //Equals "Hi there"
String firstWord = scnr.next(); //Equals "Nice"
String secondWord = scnr.next(); //Equals "to"
String thirdPart = scnr.nextLine(); //Equals "meet ya!"

I find it easiest to imagine that the Scanner constantly has a pointer in the file that it increments differently, depending on if next() or nextLine() is called.

Thanks for coming to my TED talk.