parquet-column/src/main/java/parquet/column/ColumnReader.java

/**
 * Copyright 2012 Twitter, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package parquet.column;

import parquet.io.api.Binary;

/**
 * Reader for (repetition level, definition level, values) triplets.
 * At any given point in time, a ColumnReader points to a single (r, d, v) triplet.
 * In order to move to the next triplet, call {@link #consume()}.
 *
 * Depending on the type and the encoding of the column only a subset of the get* methods are implemented.
 * Dictionary specific methods enable the upper layers to read the dictionary IDs without decoding the data.
 * In particular the Converter will decode the strings in the dictionary only once and iterate on the
 * dictionary IDs instead of the values.
 *
 * <ul>Each iteration looks at the current definition level and value as well as the next
 * repetition level:
 *  <li> The current definition level defines if the value is null.</li>
 *  <li> If the value is defined we can read it with the correct get*() method.</li>
 *  <li> Looking ahead to the next repetition determines what is the next column to read for in the FSA.</li>
 * </ul>
 * @author Julien Le Dem
  */
public interface ColumnReader {

  /**
   * @return the totalCount of values to be consumed
   */
  long getTotalValueCount();

  /**
   * Consume the current triplet, moving to the next value.
   */
  void consume();

  /**
   * must return 0 when isFullyConsumed() == true
   * @return the repetition level for the current value
   */
  int getCurrentRepetitionLevel();

  /**
   * @return the definition level for the current value
   */
  int getCurrentDefinitionLevel();

  /**
   * writes the current value to the converter
   */
  void writeCurrentValueToConverter();

  /**
   * Skip the current value
   */
  void skip();

  /**
   * available when the underlying encoding is dictionary based
   * @return the dictionary id for the current value
   */
  int getCurrentValueDictionaryID();

  /**
   * @return the current value
   */
  int getInteger();

  /**
   * @return the current value
   */
  boolean getBoolean();

  /**
   * @return the current value
   */
  long getLong();

  /**
   * @return the current value
   */
  Binary getBinary();

  /**
   * @return the current value
   */
  float getFloat();

  /**
   * @return the current value
   */
  double getDouble();

  /**
   * @return Descriptor of the column.
   */
  ColumnDescriptor getDescriptor();

}