Purpose of Java Filter Stream Classes

Filter streams in the java.io package allow developers to transform or extend the behavior of input and output streams. They provide reusable building blocks for tasks such as buffering, data conversion, or formatting. Multiple filters can be chained together, creating a flexible pipeline for processing data.

BufferedInputStream and BufferedOutputStream reduce the overhead of frequent disk or network operations by storing data in an internal buffer. Applications read or write from the buffer instead of accessing the underlying device directly. This improves performance and also enables features like rereading buffered data:

try (BufferedInputStream in = new BufferedInputStream(new FileInputStream("data.txt"))) {
    int b;
    while ((b = in.read()) != -1) {
        System.out.print((char) b);
    }
}

FilterInputStream and FilterOutputStream are abstract superclasses for filters. They delegate work to an underlying stream, while subclasses implement specialized behavior. For example, BufferedInputStream and DataInputStream extend these classes to add buffering and data-type support. Although polymorphism is possible, filter streams are usually referenced via the more general InputStream or OutputStream APIs.

DataInputStream and DataOutputStream provide methods for reading and writing primitive data types (int, double, UTF-8 Strings) in a machine-independent format, ensuring portability across platforms.

Java enforces consistent binary formats for cross-platform compatibility:

1. Big-endian for integer types (used by the JVM).
2. IEEE-754 for floating-point numbers.
3. UTF-8 for text representation.

These standards ensure that data written on one system can be reliably read on another.

• PrintStream: Simplifies writing text and primitive values. System.out and System.err are PrintStreams.
• PushbackInputStream: Allows one byte to be “unread” and pushed back into the stream, useful in parsers.

// Example: Chaining filters
try (PrintStream ps = new PrintStream(new BufferedOutputStream(new FileOutputStream("log.txt")))) {
    ps.println("Logging output efficiently.");
}

Filter streams provide flexibility by layering functionality over raw streams. They are essential for performance (buffering), data portability (DataInput/DataOutput), and developer convenience (PrintStream, PushbackInputStream). By chaining filters, Java developers can create powerful and efficient data-processing pipelines.