The allocation methods define how the files are stored in the disk blocks.
There are three main disk space or file allocation methods:
1.Contiguous Allocation-in this scheme,each file occupies a set of blocks on the disk. For example if a file requires x blocks and is given a block y as the starting location,then the blocks assigned to the file be :x,y+1,y+2,......y+x-1.
This means that given the starting block address and the length of the file(in terms of blocks required) we can determine the blocks occupied by the file.
Advantages
-both the sequential and direct accesses are supported
-this is extremely fast since the number of seeks are minimal because of contiguous allocation of file blocks.
2.linked allocation-in this scheme,each file linked list of disk blocks which need not be contiguous disk blocks can be scattered anywhere on the disk.
Advantages
it is very flexible in terms of file size.file size can be increased easily since the system does not have to look for a contiguous chunk
of memory.
this method does not suffer from external fragmentation and it makes it relatively better in terms of memory utilization.
3.Indexed Allocation-in this scheme,a special block known as the index block contains the pointers to all the blocks occupied by a file.Each file has its own index block.the entry in the index block contains the disk address of the block
Advantages
it supports direct access to the blocks occupied by the file and therefore provides fast access to the file blocks
it overcomes the problem of external fragmentation.
Answer:
The code above tries to read a file using the scanner class in java programming language.
But it was done properly.
First, the scanner class library is not imported to the program.
Second,the syntax used in this program is an invalid way of reading a file in java programming language using the scanner class.
Lastly, "String s = file.nextLine();" is not a proper way of reading each line
To correct this problem; use the following code;
import java.util.Scanner;
import java.io.File;
import java.io.FileNotFoundException;
public class ReadFileWithScanner {
try
{
public static void main(String args[]) throws FileNotFoundException {
File text = new File("data.txt");
Scanner file = new Scanner(text);
int lines = 1;
while(file.hasNextLine()){
String line = filw.nextLine();
System.out.println("line " + lines + " :" + line);
lines++;
}
catch (ArithmeticException ae)
{
System.out.println(ae.getMessage());
}
}
}
