Questions

Question 1. What class would you use to read a few pieces of data that are at known positions near the end of a large file?
Answer 1. RandomAccessFile.

Question 2.In a format call, what's the best way to indicate a new line?
Answer 2. Use the %n conversion — the \n escape is not platform independent!

Question 3. How would you append data to the end of a file? Show the constructor for the class you would use and explain your answer.
Answer 3. Here's a quick answer: Use the FileWriter and BufferedWriter classes to append data to the end of the text file. Here is the FileWriter constructor, you pass in true to write to the file in append mode:

FileWriter writer = new FileWriter (String filename, boolean append);

An alternate answer is to use RandomAccessFile and skip to the end of the file and start writing:

...
RandomAccessFile file = new RandomAccessFile(datafile, "rw");
file.skipBytes((int)file.length()); //skip to the end of the file
file.writeBytes("Add this text to the end of datafile"); //write at the end of the file
file.close();
...

Exercises

Exercise 1. Implement a pair of classes, one Reader and one Writer, that count the number of times a particular character, such as e, is read or written. The character can be specified when the stream is created. Write a program to test your classes. You can use xanadu.txt as the input file.
Answer 1. See the following three files: CounterDemo.java, CountReader.java, and CountWriter.java.

Exercise 2. The file datafile begins with a single long that tells you the offset of a single int piece of data within the same file. Using the RandomAccessFile class, write a program that gets the int piece of data. What is the int data?
Answer 2. 123. See FileReader.java for the solution. If you're interested in seeing how the file was written, see FileWriter.java.