An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.

In Core Java, an I/O filter refers to an object that reads from one stream and writes to another, effectively filtering the data as it passes through. I/O filters are part of the Java I/O (Input/Output) framework, which provides classes for reading and writing data. These classes can be chained together to create complex data processing pipelines.

In the context of I/O streams, filters are used to transform or manipulate the data as it is being read from or written to a stream. They provide a way to extend the functionality of basic streams without modifying the underlying stream classes.

For example, you can have a FileInputStream reading from a file, and you can attach a BufferedInputStream to it as a filter. The BufferedInputStream reads data in chunks, improving the overall performance by reducing the number of direct reads from the file.

Here’s a simple example:

java

FileInputStream fileInputStream = new FileInputStream("example.txt");

BufferedInputStream bufferedInputStream = new BufferedInputStream(fileInputStream);

int data = bufferedInputStream.read();
while (data != –1) {
// Process the data
System.out.print((char) data);

// Read the next byte
data = bufferedInputStream.read();
}

bufferedInputStream.close();
fileInputStream.close();

In this example, BufferedInputStream acts as an I/O filter, enhancing the reading performance of the FileInputStream.