DataSetIterator.java

/**
 * 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.metamodel.data;

import java.util.Iterator;

/**
 * Iterator implementation that iterates through a DataSet.
 */
public final class DataSetIterator implements Iterator<Row> {

	private final DataSet _dataSet;
	private volatile short _iterationState;
	private volatile Row _row;

	public DataSetIterator(DataSet dataSet) {
		_dataSet = dataSet;
		// 0 = uninitialized, 1=row not read yet, 2=row read, 3=finished
		_iterationState = 0;
	}

	@Override
	public boolean hasNext() {
		if (_iterationState == 0 || _iterationState == 2) {
			if (_dataSet.next()) {
				_iterationState = 1;
				_row = _dataSet.getRow();
			} else {
				_iterationState = 3;
				_row = null;
				_dataSet.close();
			}
		}
		return _iterationState == 1;
	}

	@Override
	public Row next() {
		if (_iterationState == 1) {
			_iterationState = 2;
		}
		return _row;
	}

	@Override
	public void remove() {
		throw new UnsupportedOperationException(
				"DataSet is read-only, remove() is not supported.");
	}

}