File Input/Output is similar to the System.out and System.in that you already have begun using. The only difference is that you read from a file.

Files

Files are another type of variable. You can make a file like this:

File f = new File("test.txt")

This does not return an exception if the file doesn't exist. To check if it does:

f.exists()

This will return a boolean.

To check if it a file or directory:

f.isFile()
f.isDirectory()

For a full list of methods you can use, go to http://java.sun.com/j2se/1.4.2/docs/api/java/io/File.html

File Output

To write to a file, you can use a FileWriter or a FileOutputStream.

FileWriter

This class writes strings or char[] to a file. To create one:

FileWriter fw = new FileWriter("test.txt");//Create a filewriter writing to test.txt
FileWriter fw = new FileWriter("test.txt", true);//Do not delete contents of file - append

It is as simple to write. After you create a FileWriterm just use:

String s = "Testing"
//INITIALIZE FileWriter fw
fw.write(s);