Using a Random Access File
Introduction
In this section, you will learn about the RandomAccess File
class provided by java.io package. This is a class that allows you to
read and write arbitrary bytes, text, and primitive Java data types from or to
any specified location in a file. As the name suggests, random that means it is
not sequential and the data can be read from and written to any specified position
in the file.
Mostly, Users use the input stream or output stream in a
sequential but Unlike the input and output streams java.io. RandomAccessFile
is used for both reading and writing files A random access file
treats with a large array of bytes stored in the file system and uses the file pointer
to deal with the indexe of that array. This file
pointer points the positions in the file where the reading or writing operation
has to be done.
Random AccessFile implements the same
interfaces as the DataInputStream and the DataOutputStream. Thus it defines the
same methods for reading and writing data to a file.
This program shows the implementation of the RandomAccessFile
class. Program takes an input from user to the name of a file and checks
if it exists then it writes the specified string using
the method writeChars( );
Otherwise it displays the appropriate message as "File does not exist".
An IOException may be thrown if the stream has
been closed.
There are following
methods has been used in this program:
RandomAccessFile rand = new RandomAccessFile(file,"rw");
The above code creates an instance of the RandomAccessFile
class mentioning the mode in which file has to be opened. The
constructor RandomAccessFile( ) takes two
arguments: First is the file name and another is the operation mode
(read-write mode). We are opening the file into read and write mode ("rw").
There are following methods that are used in the
given program shown as.
rand.seek(file.length());
This is the seek(
)
method of the RandomAccessFile
class has been used to jump the file pointer at the specified. Here, file.length(
)
returns the end of the file.
rand.close();
This is the close( ) method of the RandomAccessFile
class has been used to close the created the instance of the RandomAccessFile
class.
writeBytes(
);
This the writeBytes(
)
method which simply
writes the content into the file. This method always append the file content with
your specified text.
Here is the code of the program :
import java.io.*;
public class RandAccessFile{
public static void main(String[] args) throws IOException{
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
System.out.print("Enter File name : ");
String str = in.readLine();
File file = new File(str);
if(!file.exists())
{
System.out.println("File does not exist.");
System.exit(0);
}
try{
//Open the file for both reading and writing
RandomAccessFile rand = new RandomAccessFile(file,"rw");
rand.seek(file.length()); //Seek to end of file
rand.writeBytes("Roseindia.net,"); //Write end of file
rand.close();
System.out.println("Write
Successfully");
}
catch(IOException e)
{
System.out.println(e.getMessage());
}
}
}
|
Output of the Program:
C:\nisha>javac RandAccessFile.java
C:\nisha>java RandAccessFile
Enter File name : Filterfile.txt
Write Successfully |
Download this example.
The another program reads the characters from a file using the readByte(
) method.
import java.io.*;
public class ReadAccessFile{
public static void main(String[] args) throws IOException{
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
System.out.print("Enter File name : ");
String str = in.readLine();
File file = new File(str);
if(!file.exists())
{
System.out.println("File does not exist.");
System.exit(0);
}
try{
//Open the file for both reading and writing
RandomAccessFile rand = new RandomAccessFile(file,"r");
int i=(int)rand.length();
System.out.println("Length: " + i);
rand.seek(0); //Seek to start point of file
for(int ct = 0; ct < i; ct++){
byte b = rand.readByte();
//read byte from the file
System.out.print((char)b); //convert
byte into char
}
rand.close();
}
catch(IOException e)
{
System.out.println(e.getMessage());
}
}
}
|
Output of the Program:
C:\nisha>java ReadAccessFile
Enter File name : Filterfile.txt
Length: 30
??t h i s i s a f i l e
C:\nisha> |
Download this Program:
|
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