Java.io.LineNumberReader class in Java

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.

Constructors :

  • 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.

Methods :

  • int getLineNumber() : Get the current line number.
    Syntax :public int getLineNumber()
    Returns:
    The current line number
  • void mark(int readAheadLimit) : 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.
    Syntax :public void mark(int readAheadLimit)
              throws IOException
    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
  • int read() : 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.
    Syntax :public int read()
             throws IOException
    Returns:
    The character read, or -1 if the end of the stream has been reached
    Throws:
    IOException
  • int read(char[] cbuf, int off, int len) : Read characters into a portion of an array.Whenever a line terminator is read the current line number is incremented.
    Syntax :public int read(char[] cbuf,
           int off,
           int len)
             throws IOException
    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
  • String readLine() : Read a line of text.Whenever a line terminator is read the current line number is incremented.
    Syntax :public String readLine()
                    throws IOException
    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
  • void reset() : Reset the stream to the most recent mark.
    Syntax :public void reset()
               throws IOException
    Throws:
    IOException
  • void setLineNumber(int lineNumber) : Set the current line number.
    Syntax :public void setLineNumber(int lineNumber)
    Parameters:
    lineNumber - An int specifying the line number
  • long skip(long n) : Skip characters.
    Syntax :public long skip(long n)
              throws IOException
    Parameters:
    n - The number of characters to skip
    Returns:
    The number of characters actually skipped
    Throws:
    IOException
    IllegalArgumentException

Program :

//Java program demonstrating LineNumberReader methods
import java.io.FileReader;
import java.io.IOException;
import java.io.LineNumberReader;
class LineNumberReaderDemo
{
	public static void main(String[] args) throws IOException 
	{
		FileReader fr = new FileReader("file.txt");
		LineNumberReader lnr = new LineNumberReader(fr);
		char c[] = new char[20];

		//illustrating setLineNumber()
		lnr.setLineNumber(0);
		
		//illustrating set
		System.out.println(lnr.getLineNumber());
		
		//illustrating markSupported() method
		if(lnr.markSupported())
		{
			System.out.println("mark() method is supported");
		    //illustrating mark method
			lnr.mark(100);
		}
		
		/*File Contents
		* This is first line
		this is second line
		This is third line
		*/
		
		//skipping 19 characters
		lnr.skip(19);

		//illustrating ready() method
		if(lnr.ready())
		{
			//illustrating readLine() method
			System.out.println(lnr.readLine());

			//illustrating read(char c[],int off,int len)
			lnr.read(c);
			for (int i = 0; i <20 ; i++)
			{
				System.out.print(c[i]);
			}
			
			//illustrating reset() method
			lnr.reset();
			
			for (int i = 0; i <18 ; i++)
			{
				//illustrating read() method
				System.out.print((char)lnr.read());
			}
			int ch;
			
			//illustrating read() method
			System.out.println(lnr.readLine());
			while((ch = lnr.read())==1)
				System.out.print((char)ch);
		}
		
		//close the stream
		lnr.close();
	}
}

Output :

0
mark() method is supported
this is second line
This is third line
This is first line

This article is contributed by Nishant Sharma. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

GATE CS Corner    Company Wise Coding Practice





Writing code in comment? Please use ide.geeksforgeeks.org, generate link and share the link here.