Source code

001/*
002 * Copyright (C) 2012 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.testing;
018
019import static com.google.common.base.Preconditions.checkArgument;
020
021import com.google.common.annotations.Beta;
022import com.google.common.annotations.GwtIncompatible;
023import com.google.common.base.CharMatcher;
024import com.google.common.base.Charsets;
025import com.google.common.base.Defaults;
026import com.google.common.base.Equivalence;
027import com.google.common.base.Joiner;
028import com.google.common.base.Predicate;
029import com.google.common.base.Predicates;
030import com.google.common.base.Splitter;
031import com.google.common.base.Stopwatch;
032import com.google.common.base.Ticker;
033import com.google.common.collect.BiMap;
034import com.google.common.collect.ClassToInstanceMap;
035import com.google.common.collect.ImmutableBiMap;
036import com.google.common.collect.ImmutableClassToInstanceMap;
037import com.google.common.collect.ImmutableCollection;
038import com.google.common.collect.ImmutableList;
039import com.google.common.collect.ImmutableListMultimap;
040import com.google.common.collect.ImmutableMap;
041import com.google.common.collect.ImmutableMultimap;
042import com.google.common.collect.ImmutableMultiset;
043import com.google.common.collect.ImmutableSet;
044import com.google.common.collect.ImmutableSetMultimap;
045import com.google.common.collect.ImmutableSortedMap;
046import com.google.common.collect.ImmutableSortedMultiset;
047import com.google.common.collect.ImmutableSortedSet;
048import com.google.common.collect.ImmutableTable;
049import com.google.common.collect.Iterators;
050import com.google.common.collect.ListMultimap;
051import com.google.common.collect.MapDifference;
052import com.google.common.collect.Maps;
053import com.google.common.collect.Multimap;
054import com.google.common.collect.Multimaps;
055import com.google.common.collect.Multiset;
056import com.google.common.collect.Ordering;
057import com.google.common.collect.PeekingIterator;
058import com.google.common.collect.Range;
059import com.google.common.collect.RowSortedTable;
060import com.google.common.collect.SetMultimap;
061import com.google.common.collect.Sets;
062import com.google.common.collect.SortedMapDifference;
063import com.google.common.collect.SortedMultiset;
064import com.google.common.collect.SortedSetMultimap;
065import com.google.common.collect.Table;
066import com.google.common.collect.Tables;
067import com.google.common.collect.TreeBasedTable;
068import com.google.common.collect.TreeMultimap;
069import com.google.common.io.ByteSink;
070import com.google.common.io.ByteSource;
071import com.google.common.io.ByteStreams;
072import com.google.common.io.CharSink;
073import com.google.common.io.CharSource;
074import com.google.common.primitives.Primitives;
075import com.google.common.primitives.UnsignedInteger;
076import com.google.common.primitives.UnsignedLong;
077import java.io.ByteArrayInputStream;
078import java.io.ByteArrayOutputStream;
079import java.io.File;
080import java.io.InputStream;
081import java.io.OutputStream;
082import java.io.PrintStream;
083import java.io.PrintWriter;
084import java.io.Reader;
085import java.io.Serializable;
086import java.io.StringReader;
087import java.io.StringWriter;
088import java.io.Writer;
089import java.lang.reflect.AnnotatedElement;
090import java.lang.reflect.Array;
091import java.lang.reflect.Constructor;
092import java.lang.reflect.Field;
093import java.lang.reflect.GenericDeclaration;
094import java.lang.reflect.InvocationTargetException;
095import java.lang.reflect.Modifier;
096import java.lang.reflect.Type;
097import java.math.BigDecimal;
098import java.math.BigInteger;
099import java.nio.Buffer;
100import java.nio.ByteBuffer;
101import java.nio.CharBuffer;
102import java.nio.DoubleBuffer;
103import java.nio.FloatBuffer;
104import java.nio.IntBuffer;
105import java.nio.LongBuffer;
106import java.nio.ShortBuffer;
107import java.nio.charset.Charset;
108import java.util.ArrayDeque;
109import java.util.Arrays;
110import java.util.Collection;
111import java.util.Comparator;
112import java.util.Currency;
113import java.util.Deque;
114import java.util.Iterator;
115import java.util.List;
116import java.util.ListIterator;
117import java.util.Locale;
118import java.util.Map;
119import java.util.NavigableMap;
120import java.util.NavigableSet;
121import java.util.Optional;
122import java.util.OptionalDouble;
123import java.util.OptionalInt;
124import java.util.OptionalLong;
125import java.util.Queue;
126import java.util.Random;
127import java.util.Set;
128import java.util.SortedMap;
129import java.util.SortedSet;
130import java.util.UUID;
131import java.util.concurrent.BlockingDeque;
132import java.util.concurrent.BlockingQueue;
133import java.util.concurrent.ConcurrentHashMap;
134import java.util.concurrent.ConcurrentMap;
135import java.util.concurrent.ConcurrentNavigableMap;
136import java.util.concurrent.ConcurrentSkipListMap;
137import java.util.concurrent.CountDownLatch;
138import java.util.concurrent.Executor;
139import java.util.concurrent.LinkedBlockingDeque;
140import java.util.concurrent.ScheduledThreadPoolExecutor;
141import java.util.concurrent.ThreadFactory;
142import java.util.concurrent.ThreadPoolExecutor;
143import java.util.concurrent.TimeUnit;
144import java.util.logging.Level;
145import java.util.logging.Logger;
146import java.util.regex.MatchResult;
147import java.util.regex.Matcher;
148import java.util.regex.Pattern;
149import java.util.stream.Stream;
150import org.checkerframework.checker.nullness.qual.Nullable;
151
152/**
153 * Supplies an arbitrary "default" instance for a wide range of types, often useful in testing
154 * utilities.
155 *
156 * <p>Covers arrays, enums and common types defined in {@code java.lang}, {@code java.lang.reflect},
157 * {@code java.io}, {@code java.nio}, {@code java.math}, {@code java.util}, {@code
158 * java.util.concurrent}, {@code java.util.regex}, {@code com.google.common.base}, {@code
159 * com.google.common.collect} and {@code com.google.common.primitives}. In addition, if the type
160 * exposes at least one public static final constant of the same type, one of the constants will be
161 * used; or if the class exposes a public parameter-less constructor then it will be "new"d and
162 * returned.
163 *
164 * <p>All default instances returned by {@link #get} are generics-safe. Clients won't get type
165 * errors for using {@code get(Comparator.class)} as a {@code Comparator<Foo>}, for example.
166 * Immutable empty instances are returned for collection types; {@code ""} for string; {@code 0} for
167 * number types; reasonable default instance for other stateless types. For mutable types, a fresh
168 * instance is created each time {@code get()} is called.
169 *
170 * @author Kevin Bourrillion
171 * @author Ben Yu
172 * @since 12.0
173 */
174@Beta
175@GwtIncompatible
176public final class ArbitraryInstances {
177
178  private static final Ordering<Field> BY_FIELD_NAME =
179      new Ordering<Field>() {
180        @Override
181        public int compare(Field left, Field right) {
182          return left.getName().compareTo(right.getName());
183        }
184      };
185
186  /**
187   * Returns a new {@code MatchResult} that corresponds to a successful match. Apache Harmony (used
188   * in Android) requires a successful match in order to generate a {@code MatchResult}:
189   * http://goo.gl/5VQFmC
190   */
191  private static MatchResult newMatchResult() {
192    Matcher matcher = Pattern.compile(".").matcher("X");
193    matcher.find();
194    return matcher.toMatchResult();
195  }
196
197  private static final ClassToInstanceMap<Object> DEFAULTS =
198      ImmutableClassToInstanceMap.builder()
199          // primitives
200          .put(Object.class, "")
201          .put(Number.class, 0)
202          .put(UnsignedInteger.class, UnsignedInteger.ZERO)
203          .put(UnsignedLong.class, UnsignedLong.ZERO)
204          .put(BigInteger.class, BigInteger.ZERO)
205          .put(BigDecimal.class, BigDecimal.ZERO)
206          .put(CharSequence.class, "")
207          .put(String.class, "")
208          .put(Pattern.class, Pattern.compile(""))
209          .put(MatchResult.class, newMatchResult())
210          .put(TimeUnit.class, TimeUnit.SECONDS)
211          .put(Charset.class, Charsets.UTF_8)
212          .put(Currency.class, Currency.getInstance(Locale.US))
213          .put(Locale.class, Locale.US)
214          .put(Optional.class, Optional.empty())
215          .put(OptionalInt.class, OptionalInt.empty())
216          .put(OptionalLong.class, OptionalLong.empty())
217          .put(OptionalDouble.class, OptionalDouble.empty())
218          .put(UUID.class, UUID.randomUUID())
219          // common.base
220          .put(CharMatcher.class, CharMatcher.none())
221          .put(Joiner.class, Joiner.on(','))
222          .put(Splitter.class, Splitter.on(','))
223          .put(com.google.common.base.Optional.class, com.google.common.base.Optional.absent())
224          .put(Predicate.class, Predicates.alwaysTrue())
225          .put(Equivalence.class, Equivalence.equals())
226          .put(Ticker.class, Ticker.systemTicker())
227          .put(Stopwatch.class, Stopwatch.createUnstarted())
228          // io types
229          .put(InputStream.class, new ByteArrayInputStream(new byte[0]))
230          .put(ByteArrayInputStream.class, new ByteArrayInputStream(new byte[0]))
231          .put(Readable.class, new StringReader(""))
232          .put(Reader.class, new StringReader(""))
233          .put(StringReader.class, new StringReader(""))
234          .put(Buffer.class, ByteBuffer.allocate(0))
235          .put(CharBuffer.class, CharBuffer.allocate(0))
236          .put(ByteBuffer.class, ByteBuffer.allocate(0))
237          .put(ShortBuffer.class, ShortBuffer.allocate(0))
238          .put(IntBuffer.class, IntBuffer.allocate(0))
239          .put(LongBuffer.class, LongBuffer.allocate(0))
240          .put(FloatBuffer.class, FloatBuffer.allocate(0))
241          .put(DoubleBuffer.class, DoubleBuffer.allocate(0))
242          .put(File.class, new File(""))
243          .put(ByteSource.class, ByteSource.empty())
244          .put(CharSource.class, CharSource.empty())
245          .put(ByteSink.class, NullByteSink.INSTANCE)
246          .put(CharSink.class, NullByteSink.INSTANCE.asCharSink(Charsets.UTF_8))
247          // All collections are immutable empty. So safe for any type parameter.
248          .put(Iterator.class, ImmutableSet.of().iterator())
249          .put(PeekingIterator.class, Iterators.peekingIterator(ImmutableSet.of().iterator()))
250          .put(ListIterator.class, ImmutableList.of().listIterator())
251          .put(Iterable.class, ImmutableSet.of())
252          .put(Collection.class, ImmutableList.of())
253          .put(ImmutableCollection.class, ImmutableList.of())
254          .put(List.class, ImmutableList.of())
255          .put(ImmutableList.class, ImmutableList.of())
256          .put(Set.class, ImmutableSet.of())
257          .put(ImmutableSet.class, ImmutableSet.of())
258          .put(SortedSet.class, ImmutableSortedSet.of())
259          .put(ImmutableSortedSet.class, ImmutableSortedSet.of())
260          .put(NavigableSet.class, Sets.unmodifiableNavigableSet(Sets.newTreeSet()))
261          .put(Map.class, ImmutableMap.of())
262          .put(ImmutableMap.class, ImmutableMap.of())
263          .put(SortedMap.class, ImmutableSortedMap.of())
264          .put(ImmutableSortedMap.class, ImmutableSortedMap.of())
265          .put(NavigableMap.class, Maps.unmodifiableNavigableMap(Maps.newTreeMap()))
266          .put(Multimap.class, ImmutableMultimap.of())
267          .put(ImmutableMultimap.class, ImmutableMultimap.of())
268          .put(ListMultimap.class, ImmutableListMultimap.of())
269          .put(ImmutableListMultimap.class, ImmutableListMultimap.of())
270          .put(SetMultimap.class, ImmutableSetMultimap.of())
271          .put(ImmutableSetMultimap.class, ImmutableSetMultimap.of())
272          .put(
273              SortedSetMultimap.class,
274              Multimaps.unmodifiableSortedSetMultimap(TreeMultimap.create()))
275          .put(Multiset.class, ImmutableMultiset.of())
276          .put(ImmutableMultiset.class, ImmutableMultiset.of())
277          .put(SortedMultiset.class, ImmutableSortedMultiset.of())
278          .put(ImmutableSortedMultiset.class, ImmutableSortedMultiset.of())
279          .put(BiMap.class, ImmutableBiMap.of())
280          .put(ImmutableBiMap.class, ImmutableBiMap.of())
281          .put(Table.class, ImmutableTable.of())
282          .put(ImmutableTable.class, ImmutableTable.of())
283          .put(RowSortedTable.class, Tables.unmodifiableRowSortedTable(TreeBasedTable.create()))
284          .put(ClassToInstanceMap.class, ImmutableClassToInstanceMap.builder().build())
285          .put(ImmutableClassToInstanceMap.class, ImmutableClassToInstanceMap.builder().build())
286          .put(Comparable.class, ByToString.INSTANCE)
287          .put(Comparator.class, AlwaysEqual.INSTANCE)
288          .put(Ordering.class, AlwaysEqual.INSTANCE)
289          .put(Range.class, Range.all())
290          .put(MapDifference.class, Maps.difference(ImmutableMap.of(), ImmutableMap.of()))
291          .put(
292              SortedMapDifference.class,
293              Maps.difference(ImmutableSortedMap.of(), ImmutableSortedMap.of()))
294          // reflect
295          .put(AnnotatedElement.class, Object.class)
296          .put(GenericDeclaration.class, Object.class)
297          .put(Type.class, Object.class)
298          .build();
299
300  /**
301   * type → implementation. Inherently mutable interfaces and abstract classes are mapped to their
302   * default implementations and are "new"d upon get().
303   */
304  private static final ConcurrentMap<Class<?>, Class<?>> implementations = Maps.newConcurrentMap();
305
306  private static <T> void setImplementation(Class<T> type, Class<? extends T> implementation) {
307    checkArgument(type != implementation, "Don't register %s to itself!", type);
308    checkArgument(
309        !DEFAULTS.containsKey(type), "A default value was already registered for %s", type);
310    checkArgument(
311        implementations.put(type, implementation) == null,
312        "Implementation for %s was already registered",
313        type);
314  }
315
316  static {
317    setImplementation(Appendable.class, StringBuilder.class);
318    setImplementation(BlockingQueue.class, LinkedBlockingDeque.class);
319    setImplementation(BlockingDeque.class, LinkedBlockingDeque.class);
320    setImplementation(ConcurrentMap.class, ConcurrentHashMap.class);
321    setImplementation(ConcurrentNavigableMap.class, ConcurrentSkipListMap.class);
322    setImplementation(CountDownLatch.class, Dummies.DummyCountDownLatch.class);
323    setImplementation(Deque.class, ArrayDeque.class);
324    setImplementation(OutputStream.class, ByteArrayOutputStream.class);
325    setImplementation(PrintStream.class, Dummies.InMemoryPrintStream.class);
326    setImplementation(PrintWriter.class, Dummies.InMemoryPrintWriter.class);
327    setImplementation(Queue.class, ArrayDeque.class);
328    setImplementation(Random.class, Dummies.DeterministicRandom.class);
329    setImplementation(
330        ScheduledThreadPoolExecutor.class, Dummies.DummyScheduledThreadPoolExecutor.class);
331    setImplementation(ThreadPoolExecutor.class, Dummies.DummyScheduledThreadPoolExecutor.class);
332    setImplementation(Writer.class, StringWriter.class);
333    setImplementation(Runnable.class, Dummies.DummyRunnable.class);
334    setImplementation(ThreadFactory.class, Dummies.DummyThreadFactory.class);
335    setImplementation(Executor.class, Dummies.DummyExecutor.class);
336  }
337
338  @SuppressWarnings("unchecked") // it's a subtype map
339  @Nullable
340  private static <T> Class<? extends T> getImplementation(Class<T> type) {
341    return (Class<? extends T>) implementations.get(type);
342  }
343
344  private static final Logger logger = Logger.getLogger(ArbitraryInstances.class.getName());
345
346  /**
347   * Returns an arbitrary instance for {@code type}, or {@code null} if no arbitrary instance can be
348   * determined.
349   */
350  @Nullable
351  public static <T> T get(Class<T> type) {
352    T defaultValue = DEFAULTS.getInstance(type);
353    if (defaultValue != null) {
354      return defaultValue;
355    }
356    Class<? extends T> implementation = getImplementation(type);
357    if (implementation != null) {
358      return get(implementation);
359    }
360    if (type == Stream.class) {
361      return type.cast(Stream.empty());
362    }
363    if (type.isEnum()) {
364      T[] enumConstants = type.getEnumConstants();
365      return (enumConstants.length == 0) ? null : enumConstants[0];
366    }
367    if (type.isArray()) {
368      return createEmptyArray(type);
369    }
370    T jvmDefault = Defaults.defaultValue(Primitives.unwrap(type));
371    if (jvmDefault != null) {
372      return jvmDefault;
373    }
374    if (Modifier.isAbstract(type.getModifiers()) || !Modifier.isPublic(type.getModifiers())) {
375      return arbitraryConstantInstanceOrNull(type);
376    }
377    final Constructor<T> constructor;
378    try {
379      constructor = type.getConstructor();
380    } catch (NoSuchMethodException e) {
381      return arbitraryConstantInstanceOrNull(type);
382    }
383    constructor.setAccessible(true); // accessibility check is too slow
384    try {
385      return constructor.newInstance();
386    } catch (InstantiationException | IllegalAccessException impossible) {
387      throw new AssertionError(impossible);
388    } catch (InvocationTargetException e) {
389      logger.log(Level.WARNING, "Exception while invoking default constructor.", e.getCause());
390      return arbitraryConstantInstanceOrNull(type);
391    }
392  }
393
394  @Nullable
395  private static <T> T arbitraryConstantInstanceOrNull(Class<T> type) {
396    Field[] fields = type.getDeclaredFields();
397    Arrays.sort(fields, BY_FIELD_NAME);
398    for (Field field : fields) {
399      if (Modifier.isPublic(field.getModifiers())
400          && Modifier.isStatic(field.getModifiers())
401          && Modifier.isFinal(field.getModifiers())) {
402        if (field.getGenericType() == field.getType() && type.isAssignableFrom(field.getType())) {
403          field.setAccessible(true);
404          try {
405            T constant = type.cast(field.get(null));
406            if (constant != null) {
407              return constant;
408            }
409          } catch (IllegalAccessException impossible) {
410            throw new AssertionError(impossible);
411          }
412        }
413      }
414    }
415    return null;
416  }
417
418  private static <T> T createEmptyArray(Class<T> arrayType) {
419    return arrayType.cast(Array.newInstance(arrayType.getComponentType(), 0));
420  }
421
422  // Internal implementations of some classes, with public default constructor that get() needs.
423  private static final class Dummies {
424
425    public static final class InMemoryPrintStream extends PrintStream {
426      public InMemoryPrintStream() {
427        super(new ByteArrayOutputStream());
428      }
429    }
430
431    public static final class InMemoryPrintWriter extends PrintWriter {
432      public InMemoryPrintWriter() {
433        super(new StringWriter());
434      }
435    }
436
437    public static final class DeterministicRandom extends Random {
438      public DeterministicRandom() {
439        super(0);
440      }
441    }
442
443    public static final class DummyScheduledThreadPoolExecutor extends ScheduledThreadPoolExecutor {
444      public DummyScheduledThreadPoolExecutor() {
445        super(1);
446      }
447    }
448
449    public static final class DummyCountDownLatch extends CountDownLatch {
450      public DummyCountDownLatch() {
451        super(0);
452      }
453    }
454
455    public static final class DummyRunnable implements Runnable, Serializable {
456      @Override
457      public void run() {}
458    }
459
460    public static final class DummyThreadFactory implements ThreadFactory, Serializable {
461      @Override
462      public Thread newThread(Runnable r) {
463        return new Thread(r);
464      }
465    }
466
467    public static final class DummyExecutor implements Executor, Serializable {
468      @Override
469      public void execute(Runnable command) {}
470    }
471  }
472
473  private static final class NullByteSink extends ByteSink implements Serializable {
474    private static final NullByteSink INSTANCE = new NullByteSink();
475
476    @Override
477    public OutputStream openStream() {
478      return ByteStreams.nullOutputStream();
479    }
480  }
481
482  // Compare by toString() to satisfy 2 properties:
483  // 1. compareTo(null) should throw NullPointerException
484  // 2. the order is deterministic and easy to understand, for debugging purpose.
485  @SuppressWarnings("ComparableType")
486  private static final class ByToString implements Comparable<Object>, Serializable {
487    private static final ByToString INSTANCE = new ByToString();
488
489    @Override
490    public int compareTo(Object o) {
491      return toString().compareTo(o.toString());
492    }
493
494    @Override
495    public String toString() {
496      return "BY_TO_STRING";
497    }
498
499    private Object readResolve() {
500      return INSTANCE;
501    }
502  }
503
504  // Always equal is a valid total ordering. And it works for any Object.
505  private static final class AlwaysEqual extends Ordering<Object> implements Serializable {
506    private static final AlwaysEqual INSTANCE = new AlwaysEqual();
507
508    @Override
509    public int compare(Object o1, Object o2) {
510      return 0;
511    }
512
513    @Override
514    public String toString() {
515      return "ALWAYS_EQUAL";
516    }
517
518    private Object readResolve() {
519      return INSTANCE;
520    }
521  }
522
523  private ArbitraryInstances() {}
524}