/*
* Copyright © 2014 Cask Data, 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 co.cask.cdap.common.collect;
import com.google.common.base.Preconditions;
import com.google.common.collect.Lists;
import java.util.Collection;
import java.util.List;
/**
* This collector is used for collecting the first N elements, it returns
* false after N elements have been collected.
*
* @param <Element> Type of element.
*/
public class FirstNCollector<Element> implements Collector<Element> {
private final List<Element> elements;
private final int maxCount;
public FirstNCollector(int n) {
Preconditions.checkArgument(n > 0, "n must be greater than 0");
this.maxCount = n;
this.elements = Lists.newArrayListWithCapacity(n);
}
@Override
public boolean addElement(Element element) {
if (elements.size() >= maxCount) {
return false;
}
elements.add(element);
return (elements.size() < maxCount);
}
@Override
public <T extends Collection<? super Element>> T finish(T collection) {
collection.addAll(elements);
elements.clear();
return collection;
}
}