Java FilterReader Class

Java FilterReader class is an abstract class used to read filtered character streams.

In this chapter, we will learn what the FilterReader class is, why it is used, its declaration, constructors, methods, and examples to understand how filtering works on character input streams.

What is FilterReader Class in Java?

The FilterReader class is a character input stream that wraps another Reader and filters the data read from it.

It provides default implementations that simply pass all read requests to the underlying reader. Subclasses of FilterReader override one or more methods to modify or filter the data before it is returned to the caller.

FilterReader is mainly used when we want to transform, validate, or modify character data while reading it from an input source such as a file or string.

FilterReader Class Declaration

The FilterReader class is a part of the java.io package and extends the Reader class.

Fields of FilterReader Class

The field of FilterReader class is as follows:

Constructors of FilterReader Class

The FilterReader class provides a protected constructor that is used by its subclasses.

FilterReader(Reader in)

This constructor creates a new filtered reader that wraps the specified reader.

Syntax:

Here is the syntax:

Example of FilterReader Class Constructor

The following example demonstrates how a FilterReader subclass is created using the constructor.

Methods of FilterReader Class

The FilterReader class provides the following methods to read and manage character streams.

Examples of Java FilterReader Class

Practice the following examples to understand how the FilterReader class works in real scenarios.

Example 1: Replacing Spaces with Question Mark

The following example demonstrates how a custom FilterReader replaces spaces with a question mark (?) while reading data from a file.

File Content (javaFile123.txt):

India is my country

Output:

India?is?my?country

Example 2: Converting Characters to Uppercase While Reading

The following example demonstrates how a custom FilterReader converts all characters to uppercase while reading data from a file.

File Content (input.txt):

Java FilterReader Example

Output:

JAVA FILTERREADER EXAMPLE