public BlockCommand(int action, List<BlockTargetPair> blocktargetlist) {

    super(action);



    blocks = new Block[blocktargetlist.size()]; 

    targets = new DatanodeInfo[blocks.length][];

    for(int i = 0; i < blocks.length; i++) {

      BlockTargetPair p = blocktargetlist.get(i);

      blocks[i] = p.block;

      targets[i] = p.targets;

    }

  }