java.util.Collections.singleton()方法的使用及代码示例
本文整理了Java中java.util.Collections.singleton()方法的一些代码示例，展示了Collections.singleton()的具体用法。这些代码示例主要来源于Github/Stackoverflow/Maven等平台，是从一些精选项目中提取出来的代码，具有较强的参考意义，能在一定程度帮忙到你。Collections.singleton()方法的具体详情如下：
包路径：java.util.Collections
类名称：Collections
方法名：singleton
Collections.singleton介绍
[英]Returns a set containing the specified element. The set cannot be modified. The set is serializable.
[中]返回包含指定元素的集合。无法修改该集合。该集合是可序列化的。
代码示例
代码示例来源：origin: spring-projects/spring-framework
private Set<String> getPrefixesSet(String namespaceUri) {
Assert.notNull(namespaceUri, "No namespaceUri given");
if (this.defaultNamespaceUri.equals(namespaceUri)) {
return Collections.singleton(XMLConstants.DEFAULT_NS_PREFIX);
}
else if (XMLConstants.XML_NS_URI.equals(namespaceUri)) {
return Collections.singleton(XMLConstants.XML_NS_PREFIX);
}
else if (XMLConstants.XMLNS_ATTRIBUTE_NS_URI.equals(namespaceUri)) {
return Collections.singleton(XMLConstants.XMLNS_ATTRIBUTE);
}
else {
Set<String> prefixes = this.namespaceUriToPrefixes.get(namespaceUri);
return (prefixes != null ? Collections.unmodifiableSet(prefixes) : Collections.emptySet());
}
}代码示例来源：origin: redisson/redisson
private static Iterable<Class<?>> getClassHierarchy(Class<?> clazz) {
// Don't descend into hierarchy for RObjects
if (Arrays.asList(clazz.getInterfaces()).contains(RObject.class)) {
return Collections.<Class<?>>singleton(clazz);
}
List<Class<?>> classes = new ArrayList<Class<?>>();
for (Class<?> c = clazz; c != null; c = c.getSuperclass()) {
classes.add(c);
}
return classes;
}代码示例来源：origin: ReactiveX/RxJava
@Override
public Iterable<Integer> apply(Integer v) {
return v == 2 ? Collections.singleton(1) : Collections.<Integer>emptySet();
}
})代码示例来源：origin: apache/kafka
@Test
public void testOneConsumerNoTopic() {
String consumerId = "consumer";
Map<String, Integer> partitionsPerTopic = new HashMap<>();
Map<String, List<TopicPartition>> assignment = assignor.assign(partitionsPerTopic,
Collections.singletonMap(consumerId, new Subscription(Collections.<String>emptyList())));
assertEquals(Collections.singleton(consumerId), assignment.keySet());
assertTrue(assignment.get(consumerId).isEmpty());
}代码示例来源：origin: aragozin/jvm-tools
private static void add(Map<PoolType, Collection<String>> map, PoolType type, String name) {
if (map.containsKey(type)) {
List<String> names = new ArrayList<String>();
names.addAll(map.get(type));
names.add(name);
map.put(type, names);
}
else {
map.put(type, Collections.singleton(name));
}
}代码示例来源：origin: wildfly/wildfly
private void parseServerConfig(final XMLExtendedStreamReader reader, final String name, final PathAddress parent, List<ModelNode> list) throws XMLStreamException {
PathAddress address = parent.append(MailSubsystemModel.SERVER_TYPE, name);
final ModelNode operation = Util.createAddOperation(address);
list.add(operation);
String socketBindingRef = null;
for (int i = 0; i < reader.getAttributeCount(); i++) {
String attr = reader.getAttributeLocalName(i);
String value = reader.getAttributeValue(i);
switch (attr) {
case MailSubsystemModel.OUTBOUND_SOCKET_BINDING_REF:
socketBindingRef = value;
OUTBOUND_SOCKET_BINDING_REF.parseAndSetParameter(value, operation, reader);
break;
case MailSubsystemModel.SSL:
SSL.parseAndSetParameter(value, operation, reader);
break;
case MailSubsystemModel.TLS:
TLS.parseAndSetParameter(value, operation, reader);
break;
default:
throw ParseUtils.unexpectedAttribute(reader, i);
}
}
if (socketBindingRef == null) {
throw ParseUtils.missingRequired(reader, Collections.singleton(OUTBOUND_SOCKET_BINDING_REF));
}
parseLogin(reader, operation);
}代码示例来源：origin: redisson/redisson
/**
* Extends this key by the given method description.
*
* @param methodDescription The method to extend this key with.
* @param harmonizer The harmonizer to use for determining method equality.
* @return The harmonized key representing the extension of this key with the provided method.
*/
protected Harmonized<V> extend(MethodDescription.InDefinedShape methodDescription, Harmonizer<V> harmonizer) {
Map<V, Set<MethodDescription.TypeToken>> identifiers = new HashMap<V, Set<MethodDescription.TypeToken>>(this.identifiers);
MethodDescription.TypeToken typeToken = methodDescription.asTypeToken();
V identifier = harmonizer.harmonize(typeToken);
Set<MethodDescription.TypeToken> typeTokens = identifiers.get(identifier);
if (typeTokens == null) {
identifiers.put(identifier, Collections.singleton(typeToken));
} else {
typeTokens = new HashSet<MethodDescription.TypeToken>(typeTokens);
typeTokens.add(typeToken);
identifiers.put(identifier, typeTokens);
}
return new Harmonized<V>(internalName, parameterCount, identifiers);
}代码示例来源：origin: OryxProject/oryx
private Map<Integer,Collection<String>> getDistinctValues(JavaRDD<String[]> parsedRDD) {
int[] categoricalIndices = IntStream.range(0, inputSchema.getNumFeatures()).
filter(inputSchema::isCategorical).toArray();
return parsedRDD.mapPartitions(data -> {
Map<Integer,Collection<String>> categoryValues = new HashMap<>();
for (int i : categoricalIndices) {
categoryValues.put(i, new HashSet<>());
}
data.forEachRemaining(datum ->
categoryValues.forEach((category, values) -> values.add(datum[category]))
);
return Collections.singleton(categoryValues).iterator();
}).reduce((v1, v2) -> {
// Assumes both have the same key set
v1.forEach((category, values) -> values.addAll(v2.get(category)));
return v1;
});
}代码示例来源：origin: google/guava
public void testForMapAsMap() {
Map<String, Integer> map = Maps.newHashMap();
map.put("foo", 1);
map.put("bar", 2);
Map<String, Collection<Integer>> asMap = Multimaps.forMap(map).asMap();
assertEquals(Collections.singleton(1), asMap.get("foo"));
assertNull(asMap.get("cow"));
assertTrue(asMap.containsKey("foo"));
assertFalse(asMap.containsKey("cow"));
Set<Entry<String, Collection<Integer>>> entries = asMap.entrySet();
assertFalse(entries.contains((Object) 4.5));
assertFalse(entries.remove((Object) 4.5));
assertFalse(entries.contains(Maps.immutableEntry("foo", Collections.singletonList(1))));
assertFalse(entries.remove(Maps.immutableEntry("foo", Collections.singletonList(1))));
assertFalse(entries.contains(Maps.immutableEntry("foo", Sets.newLinkedHashSet(asList(1, 2)))));
assertFalse(entries.remove(Maps.immutableEntry("foo", Sets.newLinkedHashSet(asList(1, 2)))));
assertFalse(entries.contains(Maps.immutableEntry("foo", Collections.singleton(2))));
assertFalse(entries.remove(Maps.immutableEntry("foo", Collections.singleton(2))));
assertTrue(map.containsKey("foo"));
assertTrue(entries.contains(Maps.immutableEntry("foo", Collections.singleton(1))));
assertTrue(entries.remove(Maps.immutableEntry("foo", Collections.singleton(1))));
assertFalse(map.containsKey("foo"));
}代码示例来源：origin: apache/incubator-dubbo
private Set<String> getPackagesToScan(AnnotationMetadata metadata) {
AnnotationAttributes attributes = AnnotationAttributes.fromMap(
metadata.getAnnotationAttributes(DubboComponentScan.class.getName()));
String[] basePackages = attributes.getStringArray("basePackages");
Class<?>[] basePackageClasses = attributes.getClassArray("basePackageClasses");
String[] value = attributes.getStringArray("value");
// Appends value array attributes
Set<String> packagesToScan = new LinkedHashSet<String>(Arrays.asList(value));
packagesToScan.addAll(Arrays.asList(basePackages));
for (Class<?> basePackageClass : basePackageClasses) {
packagesToScan.add(ClassUtils.getPackageName(basePackageClass));
}
if (packagesToScan.isEmpty()) {
return Collections.singleton(ClassUtils.getPackageName(metadata.getClassName()));
}
return packagesToScan;
}代码示例来源：origin: spring-projects/spring-framework
/**
* @since 4.3
*/
@Test
public void equalsWithSameContextCustomizers() {
Set<ContextCustomizer> customizers = Collections.singleton(mock(ContextCustomizer.class));
MergedContextConfiguration mergedConfig1 = new MergedContextConfiguration(getClass(), EMPTY_STRING_ARRAY,
EMPTY_CLASS_ARRAY, null, EMPTY_STRING_ARRAY, null, null, customizers, loader, null, null);
MergedContextConfiguration mergedConfig2 = new MergedContextConfiguration(getClass(), EMPTY_STRING_ARRAY,
EMPTY_CLASS_ARRAY, null, EMPTY_STRING_ARRAY, null, null, customizers, loader, null, null);
assertEquals(mergedConfig1, mergedConfig2);
}代码示例来源：origin: apache/kafka
@Test(expected = InvalidTopicException.class)
public void testSubscriptionOnInvalidTopic() {
Time time = new MockTime();
Metadata metadata = createMetadata();
MockClient client = new MockClient(time, metadata);
initMetadata(client, Collections.singletonMap(topic, 1));
Cluster cluster = metadata.fetch();
PartitionAssignor assignor = new RoundRobinAssignor();
String invalidTopicName = "topic abc"; // Invalid topic name due to space
List<MetadataResponse.TopicMetadata> topicMetadata = new ArrayList<>();
topicMetadata.add(new MetadataResponse.TopicMetadata(Errors.INVALID_TOPIC_EXCEPTION,
invalidTopicName, false, Collections.emptyList()));
MetadataResponse updateResponse = new MetadataResponse(cluster.nodes(),
cluster.clusterResource().clusterId(),
cluster.controller().id(),
topicMetadata);
client.prepareMetadataUpdate(updateResponse);
KafkaConsumer<String, String> consumer = newConsumer(time, client, metadata, assignor, true);
consumer.subscribe(singleton(invalidTopicName), getConsumerRebalanceListener(consumer));
consumer.poll(Duration.ZERO);
}
}代码示例来源：origin: apache/kafka
@Test
public void testNoCoordinatorDiscoveryIfPositionsKnown() {
assertTrue(coordinator.coordinatorUnknown());
subscriptions.assignFromUser(singleton(t1p));
subscriptions.seek(t1p, 500L);
coordinator.refreshCommittedOffsetsIfNeeded(time.timer(Long.MAX_VALUE));
assertEquals(Collections.emptySet(), subscriptions.missingFetchPositions());
assertTrue(subscriptions.hasAllFetchPositions());
assertEquals(500L, subscriptions.position(t1p).longValue());
assertTrue(coordinator.coordinatorUnknown());
}代码示例来源：origin: google/guava
public void testRowKeyMapTailMap() {
sortedTable = create("foo", 1, 'a', "bar", 1, 'b', "foo", 3, 'c');
Map<String, Map<Integer, Character>> map = sortedTable.rowMap().tailMap("cat");
assertEquals(1, map.size());
assertEquals(ImmutableMap.of(1, 'a', 3, 'c'), map.get("foo"));
map.clear();
assertTrue(map.isEmpty());
assertEquals(Collections.singleton("bar"), sortedTable.rowKeySet());
}代码示例来源：origin: Netflix/eureka
public Set<String> getAllKnownRegions() {
String localRegion = instanceRegionChecker.getLocalRegion();
if (!remoteRegionVsApps.isEmpty()) {
Set<String> regions = remoteRegionVsApps.keySet();
Set<String> toReturn = new HashSet<String>(regions);
toReturn.add(localRegion);
return toReturn;
} else {
return Collections.singleton(localRegion);
}
}代码示例来源：origin: spring-projects/spring-framework
@Test
public void modelAttributesConventions() {
Set<String> model = Collections.singleton("bar");
Mono<RenderingResponse> result = RenderingResponse.create("foo")
.modelAttributes(model).build();
StepVerifier.create(result)
.expectNextMatches(response -> "bar".equals(response.model().get("string")))
.expectComplete()
.verify();
}代码示例来源：origin: google/guava
public void testForMapRemoveAll() {
Map<String, Integer> map = Maps.newHashMap();
map.put("foo", 1);
map.put("bar", 2);
map.put("cow", 3);
Multimap<String, Integer> multimap = Multimaps.forMap(map);
assertEquals(3, multimap.size());
assertEquals(Collections.emptySet(), multimap.removeAll("dog"));
assertEquals(3, multimap.size());
assertTrue(multimap.containsKey("bar"));
assertEquals(Collections.singleton(2), multimap.removeAll("bar"));
assertEquals(2, multimap.size());
assertFalse(multimap.containsKey("bar"));
}代码示例来源：origin: apache/kafka
@Test
public void testClearBufferedDataForTopicPartitions() {
subscriptions.assignFromUser(singleton(tp0));
subscriptions.seek(tp0, 0);
// normal fetch
assertEquals(1, fetcher.sendFetches());
assertFalse(fetcher.hasCompletedFetches());
client.prepareResponse(fullFetchResponse(tp0, this.records, Errors.NONE, 100L, 0));
consumerClient.poll(time.timer(0));
assertTrue(fetcher.hasCompletedFetches());
Set<TopicPartition> newAssignedTopicPartitions = new HashSet<>();
newAssignedTopicPartitions.add(tp1);
fetcher.clearBufferedDataForUnassignedPartitions(newAssignedTopicPartitions);
assertFalse(fetcher.hasCompletedFetches());
}代码示例来源：origin: ReactiveX/RxJava
@Test(timeout = 5000, expected = TestException.class)
public void mergeIterableOneThrows() {
Completable c = Completable.merge(Collections.singleton(error.completable));
c.blockingAwait();
}代码示例来源：origin: org.mockito/mockito-core
private void assureCanReadMockito(Set<Class<?>> types) {
if (redefineModule == null) {
return;
}
Set<Object> modules = new HashSet<Object>();
try {
Object target = getModule.invoke(Class.forName("org.mockito.internal.creation.bytebuddy.inject.MockMethodDispatcher", false, null));
for (Class<?> type : types) {
Object module = getModule.invoke(type);
if (!modules.contains(module) && !(Boolean) canRead.invoke(module, target)) {
modules.add(module);
}
}
for (Object module : modules) {
redefineModule.invoke(instrumentation, module, Collections.singleton(target),
Collections.emptyMap(), Collections.emptyMap(), Collections.emptySet(), Collections.emptyMap());
}
} catch (Exception e) {
throw new IllegalStateException(join("Could not adjust module graph to make the mock instance dispatcher visible to some classes",
"",
"At least one of those modules: " + modules + " is not reading the unnamed module of the bootstrap loader",
"Without such a read edge, the classes that are redefined to become mocks cannot access the mock dispatcher.",
"To circumvent this, Mockito attempted to add a read edge to this module what failed for an unexpected reason"), e);
}
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