ValuesReader.java

package FlexibleEncoding.Parquet;

/*
 * adapted  from Parquet*
 */
import java.io.IOException;



/**
 * Base class to implement an encoding for a given column type.
 *
 * A ValuesReader is provided with a page (byte-array) and is responsible
 * for deserializing the primitive values stored in that page.
 *
 * Given that pages are homogeneous (store only a single type), typical subclasses
 * will only override one of the read*() methods.
 *
 * @author Julien Le Dem
 */
public abstract class ValuesReader {

  /**
   * Called to initialize the column reader from a part of a page.
   *
   * The underlying implementation knows how much data to read, so a length
   * is not provided.
   *
   * Each page may contain several sections:
   * <ul>
   *  <li> repetition levels column
   *  <li> definition levels column
   *  <li> data column
   * </ul>
   *
   * This function is called with 'offset' pointing to the beginning of one of these sections,
   * and should return the offset to the section following it.
   *
   * @param valueCount count of values in this page
   * @param page the array to read from containing the page data (repetition levels, definition levels, data)
   * @param offset where to start reading from in the page
   *
   * @throws IOException
   */
  public abstract void initFromPage(int valueCount, byte[] page, int offset) throws IOException;
  
  /**
   * Called to return offset of the next section
   * @return offset of the next section
   */
  public int getNextOffset() {
    throw new ParquetDecodingException("Unsupported: cannot get offset of the next section.");
  }

  /**
   * usable when the encoding is dictionary based
   * @return the id of the next value from the page
   */
  public int readValueDictionaryId() {
    throw new UnsupportedOperationException();
  }

  /**
   * @return the next boolean from the page
   */
  public boolean readBoolean() {
    throw new UnsupportedOperationException();
  }

  /**
   * @return the next Binary from the page
   */
  public Binary readBytes() {
    throw new UnsupportedOperationException();
  }

  /**
   * @return the next float from the page
   */
  public float readFloat() {
    throw new UnsupportedOperationException();
  }

  /**
   * @return the next double from the page
   */
  public double readDouble() {
    throw new UnsupportedOperationException();
  }

  /**
   * @return the next integer from the page
   */
  public int readInteger() {
    throw new UnsupportedOperationException();
  }

  /**
   * @return the next long from the page
   */
  public long readLong() {
    throw new UnsupportedOperationException();
  }

  /**
   * Skips the next value in the page
   */
  abstract public void skip();
}