FileReader

The FileReader class creates a Reader that you can use to read the contents of a file. Its two most commonly used constructors are shown here:

FileReader(String filePath)
FileReader(File fileObj)

Either can throw a FileNotFoundException. Here, filePath is the full path name of a file, and fileObj is a File object that describes the file.

The following example shows how to read lines from a file and print these to the standard output stream. It reads its own source file, which must be in the current directory.

// Demonstrate FileReader.
import java.io.*;
class FileReaderDemo {
public static void main(String args[]) throws Exception {
FileReader fr = new FileReader("FileReaderDemo.java");
BufferedReader br = new BufferedReader(fr);
String s;
while((s = br.readLine()) != null) {
System.out.println(s);
}
fr.close();
}
}

FileWriter

FileWriter creates a Writer that you can use to write to a file. Its most commonly used constructors are shown here:

FileWriter(String filePath) 
FileWriter(String filePath, boolean append)

FileWriter(File fileObj)

They can throw an IOException or a SecurityException. Here, filePath is the full path name of a file, and fileObj is a File object that describes the file. If append is true, then output is appended to the end of the file.

Creation of a FileWriter is not dependent on the file already existing. FileWriter will create the file before opening it for output when you create the object. In the case where you attempt to open a read-only file, an IOException will be thrown.

The following example is a character stream version of an example shown earlier when FileOutputStream was discussed. This version creates a sample buffer of characters by first making a String and then using the getChars( ) method to extract the character array equivalent. It then creates three files. The first, file1.txt, will contain every other character from the sample. The second, file2.txt, will contain the entire set of characters. Finally, the third, file3.txt, will contain only the last quarter.

// Demonstrate FileWriter.
import java.io.*;
class FileWriterDemo {
public static void main(String args[]) throws Exception {
String source = "Now is the time for all good men\\n"
+ " to come to the aid of their country\\n"
+ " and pay their due taxes.";
char buffer[] = new char[source.length()];
source.getChars(0, source.length(), buffer, 0);
FileWriter f0 = new FileWriter("file1.txt");
for (int i=0; i < buffer.length; i += 2) {
f0.write(buffer[i]);
}
f0.close();
FileWriter f1 = new FileWriter("file2.txt");
f1.write(buffer);
f1.close();
FileWriter f2 = new FileWriter("file3.txt");
f2.write(buffer,buffer.lengthbuffer.
length/4,buffer.length/4);
f2.close();
}
}

2007-09-15

Comments(12)

1.	the neccessary code to create website using java By: haymanot girma at 2007-11-09 05:43:32
2.	Very useful. Just a small comment on the line: FileReader fr = new FileReader("FileReaderDemo.java"); Practically there is no need to read a java source file by a java program. It will look good if it's: FileReader fr = new FileReader("FileReaderDemo.txt"); In any case, this example is very useful. Thanks for this. By: Litty Joseph at 2008-02-06 08:37:52
3.	thanks a lot that helped.. =D By: Karthik at 2008-11-16 02:27:53
4.	The example is awesome i found it most useful among all other sites By: sabir pasha at 2009-01-20 05:11:34
5.	excellent code..... By: Anonymous at 2009-05-07 03:09:01
6.	Where should the file be placed? How do I know what the "current directory" is? I'm using the typical Eclipse structure, with src and classes directories. By: Anon at 2009-07-23 14:08:17
7.	your code helps a lot..... thanx...... By: beh at 2009-08-19 06:06:20
8.	Nice example for FileReader and FileWriter, The FileWriter code needed to be tweeked though, FileWriter f2 = new FileWriter("file3.txt"); f2.write(buffer,buffer.lengthbuffer. length/4,buffer.length/4); f2.close(); The f2.write(buffer,buffer.length/4,buffer.length/4) works better, I couldn't find a method for FileWriter.write() that took 4 arguments.... By: Tim at 2009-10-21 17:31:00
9.	Good Example ...For Both FIleWriter and FileReader.. By: karthikeyan.v at 2009-11-17 02:27:42
10.	this s seems to be writing contents into a text file can i write into excel file using file writer class? By: Iswariya at 2010-02-11 02:59:51
11.	file reader is good but file writer is worst By: sachinmani at 2010-03-01 04:34:22
12.	nice example By: pavang at 2010-07-20 01:16:22

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