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 /*
  * Copyright (C) 2009 The Guava 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.
 */
package com.google.common.collect.testing;
An implementation of Iterable which throws an exception on all invocations of the iterator() method after the first, and whose iterator is always unmodifiable.

The Iterable specification does not make it absolutely clear what should happen on a second invocation, so implementors have made various choices, including:

  • returning the same iterator again
  • throwing an exception of some kind
  • or the usual, robust behavior, which all known java.util.Collection implementations have, of returning a new, independent iterator
Because of this situation, any public method accepting an iterable should invoke the iterator method only once, and should be tested using this class. Exceptions to this rule should be clearly documented.

Note that although your APIs should be liberal in what they accept, your methods which return iterables should make every attempt to return ones of the robust variety.

This testing utility is not thread-safe.

Author(s):
Kevin Bourrillion
public final class MinimalIterable<E> implements Iterable<E> {
  
Returns an iterable whose iterator returns the given elements in order.
  public static <E> MinimalIterable<E> of(E... elements) {
    // Make sure to get an unmodifiable iterator
    return new MinimalIterable<E>(Arrays.asList(elements).iterator());
  }

  
Returns an iterable whose iterator returns the given elements in order. The elements are copied out of the source collection at the time this method is called.
  @SuppressWarnings("unchecked"// Es come in, Es go out
  public static <E> MinimalIterable<E> from(final Collection<E> elements) {
    return (MinimalIterableof(elements.toArray());
  }
  private Iterator<E> iterator;
  private MinimalIterable(Iterator<E> iterator) {
    this. = iterator;
  }
  public Iterator<E> iterator() {
    if ( == null) {
      // TODO: throw something else? Do we worry that people's code and tests
      // might be relying on this particular type of exception?
      throw new IllegalStateException();
    }
    try {
      return ;
    } finally {
       = null;
    }
  }
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