Introduction
Lets understand some I/O streams that are used to
perform reading and writing operation in a file. In the section of Java Tutorial you will learn how to
write java program to read file line by line.
Java supports the following I/O file streams.
- FileInputstream
- FileOutputStream
FileInputstream:
This class is a subclass of Inputstream class that reads bytes from a specified file name . The read()
method of this class reads a byte or array of bytes from the file. It
returns -1 when the end-of-file has been reached. We typically use
this class in conjunction with a BufferedInputStream and DataInputstream class to read binary
data. To read text data, this class is used with an InputStreamReader
and BufferedReader class. This class
throws FileNotFoundException, if the specified file is not exist.
You can use the constructor of this stream as:
FileInputstream(File
filename);
FileOutputStream:
This class is a subclass of OutputStream that writes data to a
specified file name. The write() method of
this class writes a byte or array of bytes to the file. We typically use
this class in conjunction with a BufferedOutputStream and a
DataOutputStream class to write binary
data. To write text, we typically use it with a PrintWriter, BufferedWriter
and an OutputStreamWriter class. You can use the constructor of
this stream as:
FileOutputstream(File
filename);
DataInputStream:
This class is a type of FilterInputStream
that allows you to read binary data of Java primitive data types in a
portable way. In other words, the DataInputStream
class is used to read binary Java primitive data types in a machine-independent way. An application uses a
DataOutputStream to write data that can later be read by a
DataInputStream. You can use the constructor of this stream as:
DataInputStream(FileOutputstream
finp);
The following program demonstrate, how the
contains are read from a file.
import java.io.*;
public class ReadFile{
public static void main(String[] args) throws IOException{
File f;
f=new File("myfile.txt");
if(!f.exists()&&
f.length()<0)
System.out.println("The specified file is not exist");
else{
FileInputStream finp=new FileInputStream(f);
byte b;
do{
b=(byte)finp.read();
System.out.print((char)b);
}
while(b!=-1);
finp.close();
}
}
}
|
Output of the Program:
C:\nisha>javac ReadFile.java
C:\nisha>java ReadFile
This is a text file?
C:\nisha> |
This program reads the bytes from file and display it to the user.
Download this Program
The another program use DataInputStreams for
reading textual input line by line with an appropriate
BufferedReader.
import java.io.*;
class FileRead
{
public static void main(String args[])
{
try{
// Open the file that is the first
// command line parameter
FileInputStream fstream = new FileInputStream("textfile.txt");
// Get the object of DataInputStream
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String strLine;
//Read File Line By Line
while ((strLine = br.readLine()) != null) {
// Print the content on the console
System.out.println (strLine);
}
//Close the input stream
in.close();
}catch (Exception e){//Catch exception if any
System.err.println("Error: " + e.getMessage());
}
}
}
|
Output of the Program:
| C:\nisha>javac FileRead.java
C:\nisha>java FileRead
this is a file
C:\nisha> |
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