java.io

## Class Reader

- java.lang.Object
- - java.io.Reader

- All Implemented Interfaces:
    Closeable, AutoCloseable, Readable
  Direct Known Subclasses:
    InputStreamReader

      public abstract class Reader
      extends Object
      implements Readable, Closeable

  Abstract class for reading character streams. The only methods that a subclass must implement are read(char[], int, int) and close(). Most subclasses, however, will override some of the methods defined here in order to provide higher efficiency, additional functionality, or both.
  Since:
    JDK1.1
  Author:
    Mark Reinhold
  See Also:
    `BufferedReader`, `LineNumberReader`, `CharArrayReader`, `InputStreamReader`, `FileReader`, `FilterReader`, `PushbackReader`, `PipedReader`, `StringReader`, `Writer`

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected Object` | `lock` The object used to synchronize operations on this stream.

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `Reader()` Creates a new character-stream reader whose critical sections will synchronize on the reader itself.
    `protected` | `Reader(Object lock)` Creates a new character-stream reader whose critical sections will synchronize on the given object.

  - ### Method Summary

    All Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `abstract 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)` Reads characters into an array.
    `abstract int` | `read(char[] cbuf, int off, int len)` Reads characters into a portion of an array.
    `int` | `read(CharBuffer target)` Attempts to read characters into the specified character buffer.
    `boolean` | `ready()` Tells whether this stream is ready to be read.
    `void` | `reset()` Resets the stream.
    `long` | `skip(long n)` Skips characters.

    - ### Methods inherited from class java.lang.Object

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

- - ### Field Detail

    - #### lock

          protected Object lock

      The object used to synchronize operations on this stream. For efficiency, a character-stream object may use an object other than itself to protect critical sections. A subclass should therefore use the object in this field rather than `this` or a synchronized method.

  - ### Constructor Detail

    - #### Reader

          protected Reader()

      Creates a new character-stream reader whose critical sections will synchronize on the reader itself.

    - #### Reader

          protected Reader(Object lock)

      Creates a new character-stream reader whose critical sections will synchronize on the given object.
      Parameters:
        `lock` - The Object to synchronize on.

  - ### Method Detail

    - #### read

          public int read(CharBuffer target)
                   throws IOException

      Attempts to read characters into the specified character buffer. The buffer is used as a repository of characters as-is: the only changes made are the results of a put operation. No flipping or rewinding of the buffer is performed.
      Specified by:
        `read` in interface `Readable`
      Parameters:
        `target` - the buffer to read characters into
      Returns:
        The number of characters added to the buffer, or -1 if this source of characters is at its end
      Throws:
        `IOException` - if an I/O error occurs
        `NullPointerException` - if target is null
        `ReadOnlyBufferException` - if target is a read only buffer
      Since:
        1.5

    - #### read

          public int read()
                   throws IOException

      Reads a single character. This method will block until a character is available, an I/O error occurs, or the end of the stream is reached.

      Subclasses that intend to support efficient single-character input should override this method.

      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)
                   throws IOException

      Reads characters into an array. This method will block until some input is available, an I/O error occurs, or the end of the stream is reached.
      Parameters:
        `cbuf` - Destination buffer
      Returns:
        The number of characters read, or -1 if the end of the stream has been reached
      Throws:
        `IOException` - If an I/O error occurs

    - #### read

          public abstract 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.
      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:
        `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.
      Parameters:
        `n` - The number of characters to skip
      Returns:
        The number of characters actually skipped
      Throws:
        `IllegalArgumentException` - If `n` is negative.
        `IOException` - If an I/O error occurs

    - #### ready

          public boolean ready()
                        throws IOException

      Tells whether this stream is ready to be read.
      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. The default implementation always returns false. Subclasses should override this method.
      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. Subsequent calls to reset() will attempt to reposition the stream to this point. Not all character-input streams support the mark() operation.
      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 the stream does not support mark(), or if some other I/O error occurs

    - #### reset

          public void reset()
                     throws IOException

      Resets the stream. If the stream has been marked, then attempt to reposition it at the mark. If the stream has not been marked, then attempt to reset it in some way appropriate to the particular stream, for example by repositioning it to its starting point. Not all character-input streams support the reset() operation, and some support reset() without supporting mark().
      Throws:
        `IOException` - If the stream has not been marked, or if the mark has been invalidated, or if the stream does not support reset(), or if some other I/O error occurs

    - #### close

          public abstract void close()
                              throws IOException

      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 `Closeable`
      Specified by:
        `close` in interface `AutoCloseable`
      Throws:
        `IOException` - If an I/O error occurs

Copyright © 2025 API Design. All Rights Reserved.