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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 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

Field Summary

Fields declared in class java.io.Reader

lock

Constructor Summary

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

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)`	Reads 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.

Methods declared in class java.io.BufferedReader

close, lines, markSupported, ready

Methods declared in class java.io.Reader

nullReader, read, read, skip, transferTo

Methods declared in class java.lang.Object

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

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

public int getLineNumber()

Get the current line number.

Returns:

The current line number

See Also:

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:

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

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/io/LineNumberReader.html