@InterfaceAudience.Public
@InterfaceStability.Stable
public abstract class RecordReader<KEYIN, VALUEIN> implements Closeable {

  /**
   * Called once at initialization.
   * @param split the split that defines the range of records to read
   * @param context the information about the task
   * @throws IOException
   * @throws InterruptedException
   */
  public abstract void initialize(InputSplit split,
                                  TaskAttemptContext context
                                  ) throws IOException, InterruptedException;

  /**
   * Read the next key, value pair.
   * @return true if a key/value pair was read
   * @throws IOException
   * @throws InterruptedException
   */
  public abstract 
  boolean nextKeyValue() throws IOException, InterruptedException;

  /**
   * Get the current key
   * @return the current key or null if there is no current key
   * @throws IOException
   * @throws InterruptedException
   */
  public abstract
  KEYIN getCurrentKey() throws IOException, InterruptedException;
  
  /**
   * Get the current value.
   * @return the object that was read
   * @throws IOException
   * @throws InterruptedException
   */
  public abstract 
  VALUEIN getCurrentValue() throws IOException, InterruptedException;
  
  /**
   * The current progress of the record reader through its data.
   * @return a number between 0.0 and 1.0 that is the fraction of the data read
   * @throws IOException
   * @throws InterruptedException
   */
  public abstract float getProgress() throws IOException, InterruptedException;
  
  /**
   * Close the record reader.
   */
  public abstract void close() throws IOException;
}