LineNumberReader (Java SE 11 & JDK 11 )
Keywords: java.io.LineNumberReader class

Module java.base
Package java.io

## Class LineNumberReader

- java.lang.Object
- - java.io.Reader
  - - java.io.BufferedReader
    - - java.io.LineNumberReader

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

      public class LineNumberReader
      extends BufferedReader

  A buffered character-input stream that keeps track of line numbers. This class defines methods `setLineNumber(int)` and `getLineNumber()` for setting and getting the current line number respectively.

  By default, line numbering begins at 0. This number increments at every line terminator as the data is read, and can be changed with a call to `setLineNumber(int)`. Note however, that `setLineNumber(int)` does not actually change the current position in the stream; it only changes the value that will be returned by `getLineNumber()`.

  A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a linefeed.

  Since:
    1.1

- - ### Field Summary

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

      `lock`

  - ### Constructor Summary

    Constructors
    Constructor | Description
    --- | ---
    `LineNumberReader​(Reader in)` | Create a new line-numbering reader, using the default input-buffer size.
    `LineNumberReader​(Reader in, int sz)` | Create a new line-numbering reader, reading characters into a buffer of the given size.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `int` | `getLineNumber()` | Get the current line number.
    `void` | `mark​(int readAheadLimit)` | Mark the present position in the stream.
    `int` | `read()` | Read a single character.
    `int` | `read​(char[] cbuf, int off, int len)` | Read characters into a portion of an array.
    `String` | `readLine()` | Read a line of text.
    `void` | `reset()` | Reset the stream to the most recent mark.
    `void` | `setLineNumber​(int lineNumber)` | Set the current line number.
    `long` | `skip​(long n)` | Skip characters.

    - ### Methods declared in class java.io.BufferedReader

      `lines, markSupported, ready`

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

      `close, nullReader, read, read, transferTo`

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

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

- - ### Constructor Detail

    - #### LineNumberReader

          public LineNumberReader​(Reader in)

      Create a new line-numbering reader, using the default input-buffer size.
      Parameters:
        `in` - A Reader object to provide the underlying stream

    - #### LineNumberReader

          public LineNumberReader​(Reader in,
                                  int sz)

      Create a new line-numbering reader, reading characters into a buffer of the given size.
      Parameters:
        `in` - A Reader object to provide the underlying stream
        `sz` - An int specifying the size of the buffer

  - ### Method Detail

    - #### setLineNumber

          public void setLineNumber​(int lineNumber)

      Set the current line number.
      Parameters:
        `lineNumber` - An int specifying the line number
      See Also:
        `getLineNumber()`

    - #### getLineNumber

          public int getLineNumber()

      Get the current line number.
      Returns:
        The current line number
      See Also:
        `setLineNumber(int)`

    - #### read

          public int read()
                   throws IOException

      Read a single character. Line terminators are compressed into single newline ('\n') characters. Whenever a line terminator is read the current line number is incremented.
      Overrides:
        `read` in class `BufferedReader`
      Returns:
        The character read, 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

      Read characters into a portion of an array. Whenever a line terminator is read the current line number is incremented.
      Overrides:
        `read` in class `BufferedReader`
      Parameters:
        `cbuf` - Destination buffer
        `off` - Offset at which to start storing characters
        `len` - Maximum number of characters to read
      Returns:
        The number of bytes read, or -1 if the end of the stream has already been reached
      Throws:
        `IOException` - If an I/O error occurs
        `IndexOutOfBoundsException` - If an I/O error occurs

    - #### readLine

          public String readLine()
                          throws IOException

      Read a line of text. Whenever a line terminator is read the current line number is incremented.
      Overrides:
        `readLine` in class `BufferedReader`
      Returns:
        A String containing the contents of the line, not including any line termination characters, or `null` if the end of the stream has been reached
      Throws:
        `IOException` - If an I/O error occurs
      See Also:
        `Files.readAllLines(java.nio.file.Path, java.nio.charset.Charset)`

    - #### skip

          public long skip​(long n)
                    throws IOException

      Skip characters.
      Overrides:
        `skip` in class `BufferedReader`
      Parameters:
        `n` - The number of characters to skip
      Returns:
        The number of characters actually skipped
      Throws:
        `IOException` - If an I/O error occurs
        `IllegalArgumentException` - If `n` is negative

    - #### mark

          public void mark​(int readAheadLimit)
                    throws IOException

      Mark the present position in the stream. Subsequent calls to reset() will attempt to reposition the stream to this point, and will also reset the line number appropriately.
      Overrides:
        `mark` in class `BufferedReader`
      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

      Reset the stream to the most recent mark.
      Overrides:
        `reset` in class `BufferedReader`
      Throws:
        `IOException` - If the stream has not been marked, or if the mark has been invalidated