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
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