Expanding upon @Art_Rebels' answer; To use SIGAR it requires you add the the relevant .jars
to your project and the relevant library which is dependent upon on your Operating System.
If you require help setting up SIGAR there are many posts which already exist on Stack Overflow and just a Google away, regardless if you require help just ask!
Once you have SIGAR correctly configured you can use the following snippet to display the disk usage for your C:
drive
import org.hyperic.sigar.Sigar;
public class HardDriveUsage
{
public static void main( String[] args ) throws Exception
{
Sigar sigar = new Sigar();
while (true)
{
Thread.sleep( 1000 );
System.out.println( sigar.getDiskUsage("C:") );
}
}
}