File Processing - Building Java Programs: A Back to Basics Approach - page 376

Table 6.1 Common File Extensions

Extension Description

text file

.txt

Java source code file

.java

compiled Java bytecode file

.class

Microsoft Word file

.doc

Microsoft Excel file

.xls

Adobe Portable Document File

.pdf

audio file

.mp3

image file

.jpg

compressed archive

.zip

hypertext markup language files (most often web pages)

.html

executable file

.exe

Files can be classified into text files and binary files depending on the format that
is used. Text files can be edited using simple text editors. Binary files are stored using
an internal format that requires special software to process. Text files are often stored
using the .txt extension, but other file formats are also text formats, including
.java and .html files.
To access a file from inside a Java program, you need to construct an internal
object that will represent the file. The Java class libraries include a class called File
that performs this duty.
You construct a File object by passing in the name of a file, as in the following
line of code:

File f = new File("hamlet.txt");

Once you've constructed the object, you can call a number of methods to manip-
ulate the file. For example, the following program calls a method that determines
whether a file exists, whether it can be read, what its length is (i.e., how many char-
acters are in the file), and what its absolute path is (i.e., where it is stored on the
computer):

1 // Report some basic information about a file.
2
3 import java.io.*; // for File
4
5 public class FileInfo {
6 public static void main(String[] args) {
7 File f = new File("hamlet.txt");