Module java.base
Package java.io

Class 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 at the end of the stream if the last character in the stream is not a line terminator. This number 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, or any of the previous terminators followed by end of stream, or end of stream not preceded by another terminator.

Since:
1.1
  • Constructor Details

    • 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 Details

    • 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. The current line number is incremented whenever a line terminator is read, or when the end of the stream is reached and the last character in the stream is not a line terminator.
      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
      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.

      Line terminators are compressed into single newline ('\n') characters. The current line number is incremented whenever a line terminator is read, or when the end of the stream is reached and the last character in the stream is not a line terminator.

      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 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
    • readLine

      public String readLine() throws IOException
      Read a line of text. Line terminators are compressed into single newline ('\n') characters. The current line number is incremented whenever a line terminator is read, or when the end of the stream is reached and the last character in the stream is not a line terminator.
      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)
    • 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