Find a value of the given type in the given Collection : Collections Search « Collections « Java Tutorial

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import java.util.Arrays;
import java.util.Collection;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Properties;

/*
 * Copyright 2002-2007 the original author or authors.
 *
 * 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.
 */


/**
 * Miscellaneous collection utility methods.
 * Mainly for internal use within the framework.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @since 1.1.3
 */
abstract class CollectionUtils {


  /**
   * Find a value of the given type in the given Collection.
   * @param collection the Collection to search
   * @param type the type to look for
   * @return a value of the given type found, or <code>null</code> if none
   * @throws IllegalArgumentException if more than one value of the given type found
   */
  public static Object findValueOfType(Collection collection, Class type) throws IllegalArgumentException {
    if (isEmpty(collection)) {
      return null;
    }
    Class typeToUse = (type != null ? type : Object.class);
    Object value = null;
    for (Iterator it = collection.iterator(); it.hasNext();) {
      Object obj = it.next();
      if (typeToUse.isInstance(obj)) {
        if (value != null) {
          throw new IllegalArgumentException("More than one value of type [" + typeToUse.getName() + "] found");
        }
        value = obj;
      }
    }
    return value;
  }

  /**
   * Return <code>true</code> if the supplied Collection is <code>null</code>
   * or empty. Otherwise, return <code>false</code>.
   * @param collection the Collection to check
   * @return whether the given Collection is empty
   */
  public static boolean isEmpty(Collection collection) {
    return (collection == null || collection.isEmpty());
  }

  /**
   * Return <code>true</code> if the supplied Map is <code>null</code>
   * or empty. Otherwise, return <code>false</code>.
   * @param map the Map to check
   * @return whether the given Map is empty
   */
  public static boolean isEmpty(Map map) {
    return (map == null || map.isEmpty());
  }



  /**
   * Return the first element in '<code>candidates</code>' that is contained in
   * '<code>source</code>'. If no element in '<code>candidates</code>' is present in
   * '<code>source</code>' returns <code>null</code>. Iteration order is
   * {@link Collection} implementation specific.
   * @param source the source Collection
   * @param candidates the candidates to search for
   * @return the first present object, or <code>null</code> if not found
   */
  public static Object findFirstMatch(Collection source, Collection candidates) {
    if (isEmpty(source) || isEmpty(candidates)) {
      return null;
    }
    for (Iterator it = candidates.iterator(); it.hasNext();) {
      Object candidate = it.next();
      if (source.contains(candidate)) {
        return candidate;
      }
    }
    return null;
  }


  /**
   * Determine whether the given Collection only contains a single unique object.
   * @param collection the Collection to check
   * @return <code>true</code> if the collection contains a single reference or
   * multiple references to the same instance, <code>false</code> else
   */
  public static boolean hasUniqueObject(Collection collection) {
    if (isEmpty(collection)) {
      return false;
    }
    boolean hasCandidate = false;
    Object candidate = null;
    for (Iterator it = collection.iterator(); it.hasNext();) {
      Object elem = it.next();
      if (!hasCandidate) {
        hasCandidate = true;
        candidate = elem;
      }
      else if (candidate != elem) {
        return false;
      }
    }
    return true;
  }

}