Create file with given size in Java

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Create a new RandomAccessFile and call the setLength method, specifying the desired file length. The underlying JRE implementation should use the most efficient method available in your environment.

The following program

import java.io.*;

class Test {
     public static void main(String args[]) throws Exception {
           RandomAccessFile f = new RandomAccessFile("t", "rw");
           f.setLength(1024 * 1024 * 1024);
     }
}

on a Linux machine will allocate the space using the ftruncate(2)

6070  open("t", O_RDWR|O_CREAT, 0666)   = 4
6070  fstat(4, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
6070  lseek(4, 0, SEEK_CUR)             = 0
6070  ftruncate(4, 1073741824)          = 0

while on a Solaris machine it will use the the F_FREESP64 function of the fcntl(2) system call.

/2:     open64("t", O_RDWR|O_CREAT, 0666)               = 14
/2:     fstat64(14, 0xFE4FF810)                         = 0
/2:     llseek(14, 0, SEEK_CUR)                         = 0
/2:     fcntl(14, F_FREESP64, 0xFE4FF998)               = 0

In both cases this will result in the creation of a sparse file.

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