1 /* 2 * Copyright (C) 2009 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.common.collect.testing; 18 19 import com.google.common.annotations.GwtCompatible; 20 21 import java.util.Arrays; 22 import java.util.Collection; 23 import java.util.Iterator; 24 25 /** 26 * An implementation of {@code Iterable} which throws an exception on all 27 * invocations of the {@link #iterator()} method after the first, and whose 28 * iterator is always unmodifiable. 29 * 30 * <p>The {@code Iterable} specification does not make it absolutely clear what 31 * should happen on a second invocation, so implementors have made various 32 * choices, including: 33 * 34 * <ul> 35 * <li>returning the same iterator again 36 * <li>throwing an exception of some kind 37 * <li>or the usual, <i>robust</i> behavior, which all known {@link Collection} 38 * implementations have, of returning a new, independent iterator 39 * </ul> 40 * 41 * <p>Because of this situation, any public method accepting an iterable should 42 * invoke the {@code iterator} method only once, and should be tested using this 43 * class. Exceptions to this rule should be clearly documented. 44 * 45 * <p>Note that although your APIs should be liberal in what they accept, your 46 * methods which <i>return</i> iterables should make every attempt to return 47 * ones of the robust variety. 48 * 49 * <p>This testing utility is not thread-safe. 50 * 51 * @author Kevin Bourrillion 52 */ 53 @GwtCompatible 54 public final class MinimalIterable<E> implements Iterable<E> { 55 /** 56 * Returns an iterable whose iterator returns the given elements in order. 57 */ of(E... elements)58 public static <E> MinimalIterable<E> of(E... elements) { 59 // Make sure to get an unmodifiable iterator 60 return new MinimalIterable<E>(Arrays.asList(elements).iterator()); 61 } 62 63 /** 64 * Returns an iterable whose iterator returns the given elements in order. 65 * The elements are copied out of the source collection at the time this 66 * method is called. 67 */ 68 @SuppressWarnings("unchecked") // Es come in, Es go out from(final Collection<E> elements)69 public static <E> MinimalIterable<E> from(final Collection<E> elements) { 70 return (MinimalIterable) of(elements.toArray()); 71 } 72 73 private Iterator<E> iterator; 74 MinimalIterable(Iterator<E> iterator)75 private MinimalIterable(Iterator<E> iterator) { 76 this.iterator = iterator; 77 } 78 79 @Override iterator()80 public Iterator<E> iterator() { 81 if (iterator == null) { 82 // TODO: throw something else? Do we worry that people's code and tests 83 // might be relying on this particular type of exception? 84 throw new IllegalStateException(); 85 } 86 try { 87 return iterator; 88 } finally { 89 iterator = null; 90 } 91 } 92 } 93