content: /*
   * 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 org.apache.arrow.util;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.Spliterator;
  import java.util.Spliterators;
  import java.util.stream.Collectors;
  import java.util.stream.StreamSupport;
  
  /**
   * Utility methods for manipulating {@link java.util.Collections} and their
   * subclasses/implementations.
   */
  public final class Collections2 {
    private Collections2() {}
  
    /** Creates a {@link List} from the elements remaining in iterator. */
    public static <T> List<T> toList(Iterator<T> iterator) {
      List<T> target = new ArrayList<>();
      iterator.forEachRemaining(target::add);
      return target;
    }
  
    /** Converts the iterable into a new {@link List}. */
    public static <T> List<T> toList(Iterable<T> iterable) {
      if (iterable instanceof Collection<?>) {
        // If iterable is a collection, take advantage of it for a more efficient copy
        return new ArrayList<T>((Collection<T>) iterable);
      }
      return toList(iterable.iterator());
    }
  
    /** Converts the iterable into a new immutable {@link List}. */
    public static <T> List<T> toImmutableList(Iterable<T> iterable) {
      return Collections.unmodifiableList(toList(iterable));
    }
  
    /** Copies the elements of <code>map</code> to a new unmodifiable map. */
    public static <K, V> Map<K, V> immutableMapCopy(Map<K, V> map) {
      return Collections.unmodifiableMap(new HashMap<>(map));
    }
  
    /** Copies the elements of list to a new unmodifiable list. */
    public static <V> List<V> immutableListCopy(List<V> list) {
      return Collections.unmodifiableList(new ArrayList<>(list));
    }
  
    /** Copies the values to a new unmodifiable list. */
    public static <V> List<V> asImmutableList(V... values) {
      return Collections.unmodifiableList(Arrays.asList(values));
    }
  
    /**
     * Creates a human readable string from the remaining elements in iterator.
     *
     * <p>The output should be similar to {@code Arrays#toString(Object[])}
     */
    public static String toString(Iterator<?> iterator) {
      return StreamSupport.stream(
              Spliterators.spliteratorUnknownSize(iterator, Spliterator.ORDERED), false)
          .map(String::valueOf)
          .collect(Collectors.joining(", ", "[", "]"));
    }
  }
  