Archive:Java File IO

File input/output is quite similar to the System.in and System.out that you already have begun using In Java, files can be represented by the class java.io.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 is 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 FileWriter just use:

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

FileWriter can also write in other formats. Using char[]:

Char[] charAr=s.toCharArray();//A method in class String
fw.write(charAr);

Of course, you should only use this when you already have a character array.