DatanodeDescriptor getDatanode(int index) {
assert this.triplets != null : "BlockInfo is not initialized";
assert index >= 0 && index * 3 < triplets.length : "Index is out of bound";
DatanodeDescriptor node = (DatanodeDescriptor) triplets[index * 3];
assert node == null || DatanodeDescriptor.class.getName().equals(node.getClass().getName())
: "DatanodeDescriptor is expected at " + index * 3;
return node;
}
