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Lesson: Basic I/O
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Answers to Questions and Exercises: Basic I/O

### 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`.``

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