how to change a disk size

I nead to programaticly adjust a disk size via java vCloud api... how can I do that

if I use thic sode it gives me errors like com.vmware.vcloud.sdk.VCloudException: Not a Hard Disk - SCSI Controller 0

List<VirtualDisk> disks = vm.getDisks();

for(VirtualDisk disk : vm.getDisks()){

disk.updateHardDiskSize(new BigInteger(16384+""));

}

vm.updateDisks(disks).waitForTask(0);