org.apache.hadoop.hbase.CellScanner Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.hadoop.hbase;
import java.io.IOException;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.classification.InterfaceStability;
import org.apache.hadoop.hbase.Cell;
/**
* An interface for iterating through a sequence of cells. Similar to Java's Iterator, but without
* the hasNext() or remove() methods. The hasNext() method is problematic because it may require
* actually loading the next object, which in turn requires storing the previous object somewhere.
*
* The core data block decoder should be as fast as possible, so we push the complexity and
* performance expense of concurrently tracking multiple cells to layers above the CellScanner.
*
* The {@link #current()} method will return a reference to a Cell implementation. This reference
* may or may not point to a reusable cell implementation, so users of the CellScanner should not,
* for example, accumulate a List of Cells. All of the references may point to the same object,
* which would be the latest state of the underlying Cell. In short, the Cell is mutable.
*
* Typical usage:
*
*
* while (scanner.advance()) {
* Cell cell = scanner.current();
* // do something
* }
*
* Often used reading {@link org.apache.hadoop.hbase.Cell}s written by
* {@link org.apache.hadoop.hbase.io.CellOutputStream}.
*/
@InterfaceAudience.Private
@InterfaceStability.Unstable
public interface CellScanner {
/**
* @return the current Cell which may be mutable
*/
Cell current();
/**
* Advance the scanner 1 cell.
* @return true if the next cell is found and {@link #current()} will return a valid Cell
* @throws IOException
*/
boolean advance() throws IOException;
}