Prúd zadávania znakov s vyrovnávacou pamäťou, ktorý sleduje čísla riadkov. Táto trieda definuje metódy setLineNumber(int) a getLineNumber() na nastavenie a získanie aktuálneho čísla riadku.
V predvolenom nastavení číslovanie riadkov začína na 0. Toto číslo sa zvyšuje na každom zakončení riadku pri čítaní údajov a možno ho zmeniť volaním setLineNumber(int).
Všimnite si však, že setLineNumber(int) v skutočnosti nemení aktuálnu pozíciu v prúde; zmení iba hodnotu, ktorú vráti getLineNumber().
Riadok sa považuje za ukončený ktorýmkoľvek z riadkov ('n'), návrat vozíka ('r') alebo návrat vozíka, za ktorým bezprostredne nasleduje posun riadku.
Konštruktéri:
LineNumberReader(Reader in) :
Vytvorte novú čítačku číslovania riadkov pomocou predvolenej veľkosti vstupnej vyrovnávacej pamäte.
LineNumberReader(Reader int sz) :
Vytvorte novú čítačku na čítanie riadkov do vyrovnávacej pamäte danej veľkosti. metódy:
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
Reťazec 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
dlhé preskočenie (dlhé 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
//Java program demonstrating LineNumberReader methodsimportjava.io.FileReader;importjava.io.IOException;importjava.io.LineNumberReader;classLineNumberReaderDemo{publicstaticvoidmain(String[]args)throwsIOException{FileReaderfr=newFileReader('file.txt');LineNumberReaderlnr=newLineNumberReader(fr);charc[]=newchar[20];//illustrating setLineNumber()lnr.setLineNumber(0);//illustrating setSystem.out.println(lnr.getLineNumber());//illustrating markSupported() methodif(lnr.markSupported()){System.out.println('mark() method is supported');//illustrating mark methodlnr.mark(100);}/*File Contents * This is first line this is second line This is third line *///skipping 19 characterslnr.skip(19);//illustrating ready() methodif(lnr.ready()){//illustrating readLine() methodSystem.out.println(lnr.readLine());//illustrating read(char c[]int offint len)lnr.read(c);for(inti=0;i<20;i++){System.out.print(c[i]);}//illustrating reset() methodlnr.reset();for(inti=0;i<18;i++){//illustrating read() methodSystem.out.print((char)lnr.read());}intch;//illustrating read() methodSystem.out.println(lnr.readLine());while((ch=lnr.read())==1)System.out.print((char)ch);}//close the streamlnr.close();}}
výstup:
0 mark() method is supported this is second line This is third line This is first line