Java - FilterReader Class

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Introduction

The Java.io.FilterReader class is for reading filtered character streams. Following are the important points about FilterReader −

• The class itself provides default methods that pass all requests to the contained stream.

• The Subclasses of FilterReader should override some of these methods and may also provide additional methods and fields.

Class declaration

Following is the declaration for Java.io.FilterReader class −

public abstract class FilterReader
   extends Reader

Field

Following are the fields for Java.io.FilterReader class −

• protected Reader in − This is the character-input stream.

• protected Object lock − This is the object used to synchronize operations on this stream.

Class constructors

Class methods

Methods inherited

This class inherits methods from the following classes −

• Java.io.Reader
• Java.io.Object

Example - Using close() with BufferedReader (Automatic Closure)

The following example shows the usage of Java FilterReader close() method.

FilterReaderDemo.java

package com.tutorialspoint;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class FilterReaderDemo {
   public static void main(String[] args) {
      try (BufferedReader fr = new BufferedReader(new FileReader("example.txt"))) {
         int data;
         while ((data = fr.read()) != -1) { // Read character by character
            System.out.print((char) data);
         }
         // No need to manually close, try-with-resources handles it
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output(if example.txt contains "Hello")

Let us compile and run the above program, this will produce the following result−

Hello

Explanation

• Uses BufferedReader, a subclass of FilterReader, to read "example.txt".

• Reads characters one at a time and prints them.

• Uses try-with-resources, which automatically calls close().

Example - Using mark(int readLimit) with BufferedReader

The following example shows the usage of Java FilterReader mark(int readAheadLimit) method.

FilterReaderDemo.java

package com.tutorialspoint;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class FilterReaderDemo {
   public static void main(String[] args) {
      try (BufferedReader fr = new BufferedReader(new FileReader("example.txt"))) {
         System.out.println("Mark supported? " + fr.markSupported());

         // Read and print first character
         System.out.print((char) fr.read());

         // Mark the current position
         fr.mark(5); // Can read up to 5 characters before mark expires

         // Read next two characters
         System.out.print((char) fr.read());
         System.out.print((char) fr.read());

         // Reset back to the marked position
         fr.reset();

         // Read again from the marked position
         System.out.print((char) fr.read());
         System.out.print((char) fr.read());

      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output(if example.txt contains "Hello")

Let us compile and run the above program, this will produce the following result−

Mark supported? true
Helo
elo

Explanation

• Uses BufferedReader, which supports marking.

• Marks the position after reading one character.

• Reads two more characters.

• Resets to the marked position.

• Reads again from the marked position.

Example - Reading One Character at a Time Using BufferedReader

The following example shows the usage of Java FilterReader read() method.

FilterReaderDemo.java

package com.tutorialspoint;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class FilterReaderDemo {
   public static void main(String[] args) {
      try (BufferedReader fr = new BufferedReader(new FileReader("example.txt"))) {
         int data;
         while ((data = fr.read()) != -1) { // Read character by character
            System.out.print((char) data); // Convert integer to character
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output(if example.txt contains "Hello")

Let us compile and run the above program, this will produce the following result−

Hello

Explanation

• Uses BufferedReader, a subclass of FilterReader.

• Reads one character at a time using read().

• Converts the integer ASCII/Unicode value to a character ((char) data).

• Stops when read() returns -1 (EOF reached).