FilterReader (Java SE 21 & JDK 21)
Description: declaration: module: java.base, package: java.io, class: FilterReader
Keywords: java.io.FilterReader class

Module java.base
Package java.io

# Class FilterReader

java.lang.Object
java.io.Reader
java.io.FilterReader

All Implemented Interfaces:
  `Closeable`, `AutoCloseable`, `Readable`

Direct Known Subclasses:
  `PushbackReader`

public abstract class FilterReader extends Reader
Abstract class for reading filtered character streams. The abstract class `FilterReader` itself provides default methods that pass all requests to the contained stream. Subclasses of `FilterReader` should override some of these methods and may also provide additional methods and fields.

Since:
  1.1

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected Reader`
  `in`
  The underlying character-input stream.

  ### Fields declared in class java.io.Reader

  `lock`

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `FilterReader(Reader in)`
  Creates a new filtered reader.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `close()`
  Closes the stream and releases any system resources associated with it.
  `void`
  `mark(int readAheadLimit)`
  Marks the present position in the stream.
  `boolean`
  `markSupported()`
  Tells whether this stream supports the mark() operation.
  `int`
  `read()`
  Reads a single character.
  `int`
  `read(char[] cbuf, int off, int len)`
  Reads characters into a portion of an array.
  `boolean`
  `ready()`
  Tells whether this stream is ready to be read.
  `void`
  `reset()`
  Resets the stream.
  `long`
  `skip(long n)`
  Skips characters.

  ### Methods declared in class java.io.Reader

  `nullReader, read, read, transferTo`

  ### Methods declared in class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Field Details

  - ### in

    protected Reader in
    The underlying character-input stream.

- ## Constructor Details

  - ### FilterReader

    protected FilterReader(Reader in)
    Creates a new filtered reader.
    Parameters:
      `in` - a Reader object providing the underlying stream.
    Throws:
      `NullPointerException` - if `in` is `null`

- ## Method Details

  - ### read

    public int read() throws IOException
    Reads a single character.
    Overrides:
      `read` in class `Reader`
    Returns:
      The character read, as an integer in the range 0 to 65535 (`0x00-0xffff`), or -1 if the end of the stream has been reached
    Throws:
      `IOException` - If an I/O error occurs

  - ### read

    public int read(char[] cbuf, int off, int len) throws IOException
    Reads characters into a portion of an array. This method will block until some input is available, an I/O error occurs, or the end of the stream is reached.

    If `len` is zero, then no characters are read and `0` is returned; otherwise, there is an attempt to read at least one character. If no character is available because the stream is at its end, the value `-1` is returned; otherwise, at least one character is read and stored into `cbuf`.

    Specified by:
      `read` in class `Reader`
    Parameters:
      `cbuf` - Destination buffer
      `off` - Offset at which to start storing characters
      `len` - Maximum number of characters to read
    Returns:
      The number of characters read, or -1 if the end of the stream has been reached
    Throws:
      `IndexOutOfBoundsException` - If `off` is negative, or `len` is negative, or `len` is greater than `cbuf.length - off`
      `IOException` - If an I/O error occurs

  - ### skip

    public long skip(long n) throws IOException
    Skips characters. This method will block until some characters are available, an I/O error occurs, or the end of the stream is reached. If the stream is already at its end before this method is invoked, then no characters are skipped and zero is returned.
    Overrides:
      `skip` in class `Reader`
    Parameters:
      `n` - The number of characters to skip
    Returns:
      The number of characters actually skipped
    Throws:
      `IllegalArgumentException` - If `n` is negative and the contained `Reader`'s `skip` method throws an IllegalArgumentException for a negative parameter
      `IOException` - If an I/O error occurs

  - ### ready

    public boolean ready() throws IOException
    Tells whether this stream is ready to be read.
    Overrides:
      `ready` in class `Reader`
    Returns:
      True if the next read() is guaranteed not to block for input, false otherwise. Note that returning false does not guarantee that the next read will block.
    Throws:
      `IOException` - If an I/O error occurs

  - ### markSupported

    public boolean markSupported()
    Tells whether this stream supports the mark() operation.
    Overrides:
      `markSupported` in class `Reader`
    Returns:
      true if and only if this stream supports the mark operation.

  - ### mark

    public void mark(int readAheadLimit) throws IOException
    Marks the present position in the stream.
    Overrides:
      `mark` in class `Reader`
    Parameters:
      `readAheadLimit` - Limit on the number of characters that may be read while still preserving the mark. After reading this many characters, attempting to reset the stream may fail.
    Throws:
      `IOException` - If an I/O error occurs

  - ### reset

    public void reset() throws IOException
    Resets the stream.
    Overrides:
      `reset` in class `Reader`
    Throws:
      `IOException` - If an I/O error occurs

  - ### close

    public void close() throws IOException
    Description copied from class: `Reader`
    Closes the stream and releases any system resources associated with it. Once the stream has been closed, further read(), ready(), mark(), reset(), or skip() invocations will throw an IOException. Closing a previously closed stream has no effect.
    Specified by:
      `close` in interface `AutoCloseable`
    Specified by:
      `close` in interface `Closeable`
    Specified by:
      `close` in class `Reader`
    Throws:
      `IOException` - If an I/O error occurs