Java Reference
In-Depth Information
CHAPTER 3
Input/Output
A computer program isn't much good unless it can communicate with the outside
world. This communication often takes the form of input/output (I/O); I/O capa-
bilities are a fundamental feature of any programming platform. In Java, I/O is
done with the classes and interfaces of the
java.io
package. This chapter demon-
strates many of the input/output capabilities of
java.io
. The examples here show
you how to:
•
Read and write files
•
List directories and obtain file size and date information
•
Use various Java stream classes
•
Define customized stream subclasses
The techniques introduced in this chapter are also used in other places in this
topic. We'll see many examples that use streams for input and output in Chapter 5,
Networking
, and we'll see a specialized kind of I/O in Chapter 9,
Object Serializa-
tion
.
Files and Streams
One of the commonly used classes in the
java.io
package is
File
. This class is
somewhat misleadingly named, as it represents a filename (or directory name),
rather than a file itself. Because files (and directories) have different naming con-
ventions under different operating systems, Java provides the
File
class to try to
hide some of those differences. The
File
class also defines various methods for
operating on files as a whole: deleting files, creating directories, listing directories,
querying the size and modification time of a file, and so on.
While the
File
class provides methods to manipulate directories and the files
within those directories, it doesn't provide any methods that manipulate the con-
tents of the files. In other words, it doesn't provide any way to read or write the
bytes or characters that are contained in files. In Java, sequential file I/O is
