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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;
import com.google.common.annotations.GwtCompatible;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
/**
* An implementation of {@code Iterable} which throws an exception on all invocations of the {@link
* #iterator()} method after the first, and whose iterator is always unmodifiable.
*
* <p>The {@code Iterable} specification does not make it absolutely clear what should happen on a
* second invocation, so implementors have made various choices, including:
*
* <ul>
* <li>returning the same iterator again
* <li>throwing an exception of some kind
* <li>or the usual, <i>robust</i> behavior, which all known {@link Collection} implementations
* have, of returning a new, independent iterator
* </ul>
*
* <p>Because of this situation, any public method accepting an iterable should invoke the {@code
* iterator} method only once, and should be tested using this class. Exceptions to this rule should
* be clearly documented.
*
* <p>Note that although your APIs should be liberal in what they accept, your methods which
* <i>return</i> iterables should make every attempt to return ones of the robust variety.
*
* <p>This testing utility is not thread-safe.
*
* @author Kevin Bourrillion
*/
@GwtCompatible
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<>(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(Collection<E> elements) {
return (MinimalIterable) of(elements.toArray());
}
private Iterator<E> iterator;
private MinimalIterable(Iterator<E> iterator) {
this.iterator = iterator;
}
@Override
public Iterator<E> iterator() {
if (iterator == 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 iterator;
} finally {
iterator = null;
}
}
}
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