CSC1110 Exercise 12

File Input/Output

Reading and writing files is one of the most common actions in modern programming. All data is stored in a file somewhere, so to use data in any capacity, we need to be able to store it in files and read it from files into memory. There are many ways to read and write files in Java, but we will focus on three in this exercise:

• Pure text
• Binary data
• Binary objects

Text File I/O

There are numerous ways to read and write text files in Java. The simplest way to read text from an existing text file is to use a Scanner object. A Scanner is quite flexible in that it can read text from a variety of sources, as long as that source gives the Scanner a String. Some examples of sources for a Scanner are

• System.in - Keyboard input
• String objects - Will be read as if the String were typed in
• Paths/Files - Will attempt to read the file referenced by the Path or File object

Note that to have a Scanner read from a file, you would need to pass in a File or Path object, not just the filename. This is because the filename is a String and would be read by the Scanner as a String.

To write to a text file, the simplest way is to use a PrintWriter object. The PrintWriter uses the same methods that System.out uses, such as println(), print(), printf(), etc.

Binary File I/O

To store non-text data, we can use binary files to efficiently store primitive data types. This is done using the DataInputStream and DataOutoutStream objects. Both of these require a FileInputStream or FileOutputStream parameter to interface with the File itself. These streams only need a filename to access the data.

Object File I/O

In Java, there are times when it is necessary to save instances of an objects. Rather than save each individual instance variable, then reload them into new objects, we can store entire objects into a file using the ObjectOutputStream and ObjectInputStream objects. Like the binary files above, a FileInputStream or FileOutputStream is required for these objects.

Exercise

You have been given some values that you will need to store in all three of these types of files. There is a provided Dyad record to store integer values for writing an object. You should write the data to three separate files, handling any checked exceptions that arise with useful messages. Once you have written the files, you will then create variables (two for each file) and read in your three files. Print out your variables to verify that your data was successfully written and read,

Submission Instructions

Commit and push your code to your repository.