content: /**
   * Copyright The Apache Software Foundation
   *
   * 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 com.alibaba.tac.engine.util;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.List;
  
  /**
   * Utility methods for dealing with Collections, including treating null
   * collections as empty.
   */
  public class CollectionUtils {
  
    private static final List<Object> EMPTY_LIST = Collections
        .unmodifiableList(new ArrayList<Object>(0));
  
    @SuppressWarnings("unchecked")
    public static <T> Collection<T> nullSafe(Collection<T> in) {
      if (in == null) {
        return (Collection<T>) EMPTY_LIST;
      }
      return in;
    }
  
    /************************ size ************************************/
  
    public static <T> int nullSafeSize(Collection<T> collection) {
      if (collection == null) {
        return 0;
      }
      return collection.size();
    }
  
    public static <A, B> boolean nullSafeSameSize(Collection<A> a, Collection<B> b) {
      return nullSafeSize(a) == nullSafeSize(b);
    }
  
    /*************************** empty ****************************************/
  
    public static <T> boolean isEmpty(Collection<T> collection) {
      return collection == null || collection.isEmpty();
    }
  
    public static <T> boolean notEmpty(Collection<T> collection) {
      return !isEmpty(collection);
    }
  
    /************************ first/last **************************/
  
    public static <T> T getFirst(Collection<T> collection) {
      if (CollectionUtils.isEmpty(collection)) {
        return null;
      }
      for (T t : collection) {
        return t;
      }
      return null;
    }
  
    /**
     * @param list any list
     * @return -1 if list is empty, otherwise the max index
     */
    public static int getLastIndex(List<?> list) {
      if (isEmpty(list)) {
        return -1;
      }
      return list.size() - 1;
    }
  
    /**
     * @param list
     * @param index the index in question
     * @return true if it is the last index or if list is empty and -1 is passed
     *         for the index param
     */
    public static boolean isLastIndex(List<?> list, int index) {
      return index == getLastIndex(list);
    }
  
    public static <T> T getLast(List<T> list) {
      if (isEmpty(list)) {
        return null;
      }
      return list.get(list.size() - 1);
    }
  }
  