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Collection Query Engine: NoSQL indexing and query engine for Java collections with ultra-low latency
There is a newer version: 3.6.0
/**
 * Copyright 2012-2015 Niall Gallagher
 *
 * 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 com.googlecode.cqengine.resultset.common;

import com.googlecode.cqengine.resultset.ResultSet;

import java.util.*;

/**
 * Utility methods for working with {@link com.googlecode.cqengine.resultset.ResultSet} objects.
 *
 * @author Niall Gallagher
 */
public class ResultSets {

    /**
     * Returns a Collection-like view of the given ResultSet.
     * 
     * The collection simply delegates to the ResultSet, which in turn will reflect
     * any changes made to the underlying IndexedCollection by other threads.
     * For example consecutive calls to the size() method
     * may return different values if objects are added to or removed from the IndexedCollection.
     *
     * @param resultSet The ResultSet to wrap
     * @return A Collection-like view of the given ResultSet
     */
    public static  Collection asCollection(final ResultSet resultSet) {
        return new AbstractCollection() {
            @Override
            public Iterator iterator() {
                return resultSet.iterator();
            }
            @Override
            public int size() {
                return resultSet.size();
            }

            @Override
            public boolean contains(Object o) {
                @SuppressWarnings("unchecked")
                O object = (O)o;
                return resultSet.contains(object);
            }

            @Override
            public boolean isEmpty() {
                return resultSet.isEmpty();
            }
        };
    }

    /**
     * Returns a list of {@link CostCachingResultSet}s, by copying from the result sets given, wrapping them as
     * necessary via {@link #wrapWithCostCachingIfNecessary(ResultSet)}.
     *
     * @param resultSets a list of {@link CostCachingResultSet}s
     */
    public static  List> wrapWithCostCachingIfNecessary(Iterable> resultSets) {
        List> result = new LinkedList>();
        for (ResultSet candidate : resultSets) {
            result.add(wrapWithCostCachingIfNecessary(candidate));
        }
        return result;
    }

    /**
     * Returns the given {@link ResultSet} as-is if it is already an instance of {@link CostCachingResultSet}, otherwise
     * wraps it accordingly and returns the result.
     * @param resultSet A {@link ResultSet} which may or may not be an instance of {@link CostCachingResultSet}
     * @return A {@link CostCachingResultSet} as described
     */
    public static  ResultSet wrapWithCostCachingIfNecessary(final ResultSet resultSet) {
        return resultSet instanceof CostCachingResultSet ? resultSet : new CostCachingResultSet(resultSet);
    }

    /**
     * Private constructor, not used.
     */
    ResultSets() {
    }
}