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 java.util.Arrays; 20 import java.util.Collection; 21 import java.util.Iterator; 22 23 /** 24 * An implementation of {@code Iterable} which throws an exception on all 25 * invocations of the {@link #iterator()} method after the first, and whose 26 * iterator is always unmodifiable. 27 * 28 * <p>The {@code Iterable} specification does not make it absolutely clear what 29 * should happen on a second invocation, so implementors have made various 30 * choices, including: 31 * 32 * <ul> 33 * <li>returning the same iterator again 34 * <li>throwing an exception of some kind 35 * <li>or the usual, <i>robust</i> behavior, which all known {@link Collection} 36 * implementations have, of returning a new, independent iterator 37 * </ul> 38 * 39 * Because of this situation, any public method accepting an iterable should 40 * invoke the {@code iterator} method only once, and should be tested using this 41 * class. Exceptions to this rule should be clearly documented. 42 * 43 * <p>Note that although your APIs should be liberal in what they accept, your 44 * methods which <i>return</i> iterables should make every attempt to return 45 * ones of the robust variety. 46 * 47 * <p>This testing utility is not thread-safe. 48 * 49 * @author Kevin Bourrillion 50 */ 51 public final class MinimalIterable<E> implements Iterable<E> { 52 /** 53 * Returns an iterable whose iterator returns the given elements in order. 54 */ of(E... elements)55 public static <E> MinimalIterable<E> of(E... elements) { 56 // Make sure to get an unmodifiable iterator 57 return new MinimalIterable<E>(Arrays.asList(elements).iterator()); 58 } 59 60 /** 61 * Returns an iterable whose iterator returns the given elements in order. 62 * The elements are copied out of the source collection at the time this 63 * method is called. 64 */ 65 @SuppressWarnings("unchecked") // Es come in, Es go out from(final Collection<E> elements)66 public static <E> MinimalIterable<E> from(final Collection<E> elements) { 67 return (MinimalIterable) of(elements.toArray()); 68 } 69 70 private Iterator<E> iterator; 71 MinimalIterable(Iterator<E> iterator)72 private MinimalIterable(Iterator<E> iterator) { 73 this.iterator = iterator; 74 } 75 76 @Override iterator()77 public Iterator<E> iterator() { 78 if (iterator == null) { 79 // TODO: throw something else? Do we worry that people's code and tests 80 // might be relying on this particular type of exception? 81 throw new IllegalStateException(); 82 } 83 try { 84 return iterator; 85 } finally { 86 iterator = null; 87 } 88 } 89 } 90