[Chapter 11] FilterReader
Author: Mark Grand and Jonathan Knudsen
Date: Fri Aug 8 16:37:21 1997

#

| Chapter 11 The java.io Package |

# FilterReader

## Name

FilterReader

## Synopsis

Class Name:

  `java.io.FilterReader`

Superclass:

  `java.io.Reader`

Immediate Subclasses:

  `java.io.PushbackReader`

Interfaces Implemented:

  None

Availability:

  New as of JDK 1.1

## Description

The `FilterReader` class is the superclass of all of the reader classes that filter input. A subclass of `FilterReader` works by wrapping an existing reader, called the underlying reader, and providing additional functionality. The methods of `FilterReader` simply override the methods of `Reader` with versions that call the corresponding methods of the underlying reader.

`FilterReader` cannot be instantiated directly; it must be subclassed. An instance of a subclass of `FilterReader` is constructed with another `Reader` object. The methods of a subclass of `FilterReader` should override some methods in order to extend their behavior or provide some sort of filtering.

`FilterReader` is like `FilterInputStream`, except that it deals with a character stream instead of a byte stream.

## Class Summary

    public abstract class java.io.FilterReader extends java.io.Reader {
      // Variables
      protected Reader in;
      // Constructors
      protected FilterReader(Reader in);
      // Instance Methods
      public void close();
      public void mark(int readAheadLimit);
      public boolean markSupported();
      public int read();
      public int read(char[] cbuf, int off, int len);
      public boolean ready();
      public void reset();
      public long skip(long n);
    }

## Variables

### in

#### protected Reader in

Description

  The underlying reader that this `FilterReader` wraps or filters.

## Constructors

### FilterReader

#### protected FilterReader(Reader in)

Parameters

  `in`

    The input reader to filter.

Description

  This constructor creates a `FilterReader` that gets data from `in`.

## Instance Methods

### close

#### public void close() throws IOException

Throws

  `IOException`

    If any kind of I/O error occurs.

Overrides

  `Reader.close()`

Description

  This method calls the `close()` method of the underlying reader, which releases any system resources associated with this object.

### mark

#### public void mark(int readAheadLimit) throws IOException

Parameters

  `readAheadLimit`

    The maximum number of characters that can be read before the saved position becomes invalid.

Throws

  `IOException`

    If any kind of I/O error occurs.

Overrides

  `Reader.mark()`

Description

  This method calls the `mark()` method of the underlying reader. If the underlying reader supports `mark()` and `reset()`, this method causes the `FilterReader` to remember its current position. A subsequent call to `reset()` causes the object to return to that saved position, and thus re-read a portion of the input.

### markSupported

#### public boolean markSupported()

Returns

  `true` if this reader supports `mark()` and `reset()`; `false` otherwise.

Overrides

  `Reader.markSupported()`

Description

  This method calls the `markSupported()` method of the underlying reader and returns the result.

### read

#### public int read() throws IOException

Returns

  The next character of data or `-1` if the end of the stream is encountered.

Throws

  `IOException`

    If any kind of I/O error occurs.

Overrides

  `Reader.read()`

Description

  This method calls the `read()` method of the underlying reader and returns the result. The method blocks until data is available, the end of the stream is detected, or an exception is thrown.

#### public int read(char[] cbuf, int off, int len) throws IOException

Parameters

  `cbuf`

    An array of characters to be filled from the stream.

  `off`

    An offset into the array.

  `len`

    The number of characters to read.

Returns

  The actual number of characters read or `-1` if the end of the stream is encountered immediately.

Throws

  `IOException`

    If any kind of I/O error occurs.

Overrides

  `Reader.read(char[], int, int)`

Description

  This method reads up to `len` characters of input into the given array starting at index `off`. It does this by calling the `read(char[], int, int)` method of the underlying reader and returning the result. The method blocks until some data is available.

### ready

#### public boolean ready() throws IOException

Returns

  A `boolean` value that indicates whether the reader is ready to be read.

Throws

  `IOException`

    If the stream is closed.

Overrides

  `Reader.ready()`

Description

  This method calls the `ready()` method of the underlying reader and returns the result. If the underlying stream is ready, this method returns `true`. The underlying stream is ready if the next `read()` is guaranteed not to block.

### reset

#### public void reset() throws IOException

Throws

  `IOException`

    If the stream is closed, `mark()` has not been called, or the saved position has been invalidated.

Overrides

  `Reader.reset()`

Description

  This method calls the `reset()` method of the underlying reader. If the underlying reader supports `mark()` and `reset()`, this method sets the position of the `FilteredReader` to a position that was saved by a previous call to `mark()`. Subsequent characters read from this `FilteredReader` will begin from the saved position and continue normally.

### skip

#### public long skip(long n) throws IOException

Parameters

  `n`

    The number of characters to skip.

Returns

  The actual number of characters skipped.

Throws

  `IOException`

    If any kind of I/O error occurs.

Overrides

  `Reader.skip()`

Description

  This method skips `n` characters of input. It calls the `skip()` method of the underlying reader.

## Inherited Methods

Method | Inherited From | Method | Inherited From
--- | --- | --- | ---
`clone()` | `Object` | `equals(Object)` | `Object`
`finalize()` | `Object` | `getClass()` | `Object`
`hashCode()` | `Object` | `notify()` | `Object`
`notifyAll()` | `Object` | `toString()` | `Object`
`wait()` | `Object` | `wait(long)` | `Object`
`wait(long, int)` | `Object` |  |

## See Also

`FilterInputStream`, `IOException`, `PushbackReader`, `Reader`

FilterOutputStream |  | FilterWriter