CompositeRecordReader.java 文件源码

/**
 * Create a RecordReader with <tt>capacity</tt> children to position
 * <tt>id</tt> in the parent reader.
 * The id of a root CompositeRecordReader is -1 by convention, but relying
 * on this is not recommended.
 */
@SuppressWarnings("unchecked") // Generic array assignment
public CompositeRecordReader(int id, int capacity,
    Class<? extends WritableComparator> cmpcl)
    throws IOException {
  assert capacity > 0 : "Invalid capacity";
  this.id = id;
  if (null != cmpcl) {
    cmp = ReflectionUtils.newInstance(cmpcl, null);
    q = new PriorityQueue<ComposableRecordReader<K,?>>(3,
        new Comparator<ComposableRecordReader<K,?>>() {
          public int compare(ComposableRecordReader<K,?> o1,
                             ComposableRecordReader<K,?> o2) {
            return cmp.compare(o1.key(), o2.key());
          }
        });
  }
  jc = new JoinCollector(capacity);
  kids = new ComposableRecordReader[capacity];
}