001/* 002 * Copyright (C) 2009 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package com.google.common.collect.testing; 018 019import com.google.common.annotations.GwtCompatible; 020import java.util.Arrays; 021import java.util.Collection; 022import java.util.Iterator; 023 024/** 025 * An implementation of {@code Iterable} which throws an exception on all invocations of the {@link 026 * #iterator()} method after the first, and whose iterator is always unmodifiable. 027 * 028 * <p>The {@code Iterable} specification does not make it absolutely clear what should happen on a 029 * second invocation, so implementors have made various choices, including: 030 * 031 * <ul> 032 * <li>returning the same iterator again 033 * <li>throwing an exception of some kind 034 * <li>or the usual, <i>robust</i> behavior, which all known {@link Collection} implementations 035 * have, of returning a new, independent iterator 036 * </ul> 037 * 038 * <p>Because of this situation, any public method accepting an iterable should invoke the {@code 039 * iterator} method only once, and should be tested using this class. Exceptions to this rule should 040 * be clearly documented. 041 * 042 * <p>Note that although your APIs should be liberal in what they accept, your methods which 043 * <i>return</i> iterables should make every attempt to return ones of the robust variety. 044 * 045 * <p>This testing utility is not thread-safe. 046 * 047 * @author Kevin Bourrillion 048 */ 049@GwtCompatible 050public final class MinimalIterable<E> implements Iterable<E> { 051 /** Returns an iterable whose iterator returns the given elements in order. */ 052 public static <E> MinimalIterable<E> of(E... elements) { 053 // Make sure to get an unmodifiable iterator 054 return new MinimalIterable<E>(Arrays.asList(elements).iterator()); 055 } 056 057 /** 058 * Returns an iterable whose iterator returns the given elements in order. The elements are copied 059 * out of the source collection at the time this method is called. 060 */ 061 @SuppressWarnings("unchecked") // Es come in, Es go out 062 public static <E> MinimalIterable<E> from(final Collection<E> elements) { 063 return (MinimalIterable) of(elements.toArray()); 064 } 065 066 private Iterator<E> iterator; 067 068 private MinimalIterable(Iterator<E> iterator) { 069 this.iterator = iterator; 070 } 071 072 @Override 073 public Iterator<E> iterator() { 074 if (iterator == null) { 075 // TODO: throw something else? Do we worry that people's code and tests 076 // might be relying on this particular type of exception? 077 throw new IllegalStateException(); 078 } 079 try { 080 return iterator; 081 } finally { 082 iterator = null; 083 } 084 } 085}