Java 中的 Java.io.LineNumberReader 类
原文:https://www . geesforgeks . org/Java-io-line number reader-class-Java/
跟踪行号的缓冲字符输入流。这个类定义了 setLineNumber(int)和 getLineNumber()方法，分别用于设置和获取当前行号。
- By default, the line number starts at 0. When reading data, the number is incremented at each line terminator and can be changed by calling setLineNumber(int).
- Note, however, that setLineNumber(int) does not actually change the current position in the stream; It only changes the value that getLineNumber () will return.
- A line is considered to be ended by any one of line feed ('\n'), carriage return ('\r') or carriage return immediately following the line feed.
构造函数:
- Line number reader (reader in): Create a new line number reader using the default input buffer size.
- Reader in (int SZ): Create a new line reader to read characters into a buffer of a given size.
方法:
-
线号()线粗.
java Syntax :public int getLineNumber() Returns: The current line number -
Invalid mark (int readahead limit): Mark the current position in the stream. Subsequent calls to reset () will attempt to relocate the stream to this point and will reset the line number appropriately.
java 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. The line terminator is compressed into a single line feed ('\n'). Whenever the line terminator is read, the current line number is incremented.
java 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 part of the array. Whenever the line terminator is read, the current line number is incremented.
java 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 the line terminator is read, the current line number is incremented.
java 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 nearest mark.
java Syntax :public void reset() throws IOException Throws: IOException -
无效设置行号(内部行号):设置当前行号
java Syntax :public void setLineNumber(int lineNumber) Parameters: lineNumber - An int specifying the line number -
Long skip (length n): Skip characters.
java 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 IllegalArgumentExceptionT42
程序:
//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();
}
}
输出:
0
mark() method is supported
this is second line
This is third line
This is first line
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