001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.reef.util;
020
021import java.util.Collection;
022
023/**
024 * Utility functions for arrays and collection classes.
025 */
026public final class CollectionUtils {
027
028  private CollectionUtils() {
029    // avoid instantiation
030  }
031
032  /**
033   * Checks if the collection is null or empty.
034   * @param <T> a type of element of collection
035   * @param parameter the collection
036   * @return true if the collection is null or empty
037   */
038  public static <T> boolean isEmpty(final Collection<T> parameter) {
039    return parameter == null || parameter.isEmpty();
040  }
041
042  /**
043   * Checks if the collection is not null and not empty.
044   * @param <T> a type of element of collection
045   * @param parameter the collection
046   * @return true if the collection is not null nor empty
047   */
048  public static <T> boolean isNotEmpty(final Collection<T> parameter) {
049    return !isEmpty(parameter);
050  }
051
052  private static final Object[] EMPTY_ARRAY = new Object[0];
053
054  /**
055   * Return an empty array if input is null; works as identity function otherwise.
056   * This function is useful in `for` statements if the iterable can be null.
057   * @param array Input array. Can be null.
058   * @param <T> Type of the elements of the array.
059   * @return A reference to the input array if it is not null, an empty array otherwise.
060   */
061  @SuppressWarnings("unchecked")
062  public static <T> T[] nullToEmpty(final T[] array) {
063    return array == null ? (T[])EMPTY_ARRAY : array;
064  }
065}