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Working with Filtered Streams

You attach a filtered stream to another stream to filter the data as it's read from or written to the original stream. The java.io package contains these filtered streams which are subclasses of either FilterInputStream or FilterOutputStream:

• DataInputStream and DataOutputStream
• BufferedInputStream and BufferedOutputStream
• LineNumberInputStream
• PushbackInputStream
• PrintStream (this is an output stream)

This section shows you how to use filtered streams through an example that uses a DataInputStream and a DataOutputStream. In addition, this section shows you how to write your own filtered streams.

Using Filtered Streams

[PENDING: readLine has been deprecated. UPdate this section as per book, and book in new psuedo-code here]

To use a filtered input or output stream, attach the filtered stream to another input or output stream. For example, you can attach a DataInputStream to the standard input stream as in the following code:

DataInputStream dis = new DataInputStream(System.in);
String input;

while ((input = dis.readLine()) != null) {
    . . . // do something interesting here
}

You might do this so that you can use the more convenient readXXX methods, such as readLine, implemented by DataInputStream.

How to Use DataInputStream and DataOutputStream

This page provides and explains an example of using DataInputStream and DataOutputStream, two filtered streams that can read and write primitive Java data types.

Writing Your Own Filtered Streams

Many programmers find that they need to implement their own streams that filter or process data as it is being written to or read from the stream. Sometimes the processing is independent of the format of the data, such as counting various items in the stream, and sometimes the processing is directly related to the data itself or the format of the data, such as reading and writing data that is contained in rows and columns. Often, these programmers subclass FilterOutputStream and FilterInputStream to achieve their goals. This section describes an example of how to subclass FileInputStream and FilterOutputStream to create your own filtered streams.

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