Cả hai là tương đương và bên dưới chúng giống nhau, nhưng tôi sẽ đễ xuất `Union` thay cho `Optional` vì từ "**tùy chọn**" có vẻ ngầm định giá trị là tùy chọn, và nó thực sự có nghĩa rằng "nó có thể là `None`", do đó nó không phải là tùy chọn và nó vẫn được yêu cầu.

Tôi nghĩ `Union[SomeType, None]` là rõ ràng hơn về ý nghĩa của nó.

Nó chỉ là về các từ và tên. Nhưng những từ đó có thể ảnh hưởng cách bạn và những đồng đội của bạn suy nghĩ về code.

import com.google.common.collect.testing.features.CollectionSize;
import java.util.Collection;
import java.util.Set;
import org.junit.Ignore;

/**
 * Tests {@link java.util.Set#equals}.
 *
 * @author George van den Driessche
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.

import com.google.common.collect.testing.features.CollectionSize;
import java.util.Collection;
import java.util.Set;
import org.junit.Ignore;

/**
 * Tests {@link java.util.Set#equals}.
 *
 * @author George van den Driessche
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import org.junit.Ignore;

/**
 * Tests {@link List#equals}.
 *
 * @author George van den Driessche
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.

import java.util.Collection;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.SortedSet;

/**
 * Optional features of classes derived from {@code Collection}.
 *
 * @author George van den Driessche
 */
@SuppressWarnings("rawtypes") // maybe avoidable if we rework the whole package?
@GwtCompatible
public enum CollectionFeature implements Feature<Collection> {
  /**

 *     instance of G should somehow provide an instance of the class under test, plus any other
 *     information required to parameterize the test.
 * @see FeatureSpecificTestSuiteBuilder
 * @author George van den Driessche
 */
@GwtIncompatible
public abstract class PerCollectionSizeTestSuiteBuilder<
        B extends PerCollectionSizeTestSuiteBuilder<B, G, T, E>,
        G extends TestContainerGenerator<T, E>,
        T,

import org.junit.Ignore;

/**
 * A generic JUnit test which tests {@code set()} operations on a list. Can't be invoked directly;
 * please see {@link com.google.common.collect.testing.ListTestSuiteBuilder}.
 *
 * @author George van den Driessche
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.

import org.junit.Ignore;

/**
 * A generic JUnit test which tests {@code remove} operations on a map. Can't be invoked directly;
 * please see {@link com.google.common.collect.testing.MapTestSuiteBuilder}.
 *
 * @author George van den Driessche
 * @author Chris Povirk
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")

import java.util.List;
import java.util.Set;
import junit.framework.TestSuite;

/**
 * Creates, based on your criteria, a JUnit test suite that exhaustively tests a List
 * implementation.
 *
 * @author George van den Driessche
 */
@GwtIncompatible
public final class ListTestSuiteBuilder<E>
    extends AbstractCollectionTestSuiteBuilder<ListTestSuiteBuilder<E>, E> {

 *
 * <p>See {@link TestingExecutors#sameThreadScheduledExecutor()} for a full list of constraints.
 *
 * @author John Sirois
 * @author Zach van Schouwen
 */
@GwtIncompatible
// TODO(cpovirk): Make this final (but that may break Mockito spy calls).
class SameThreadScheduledExecutorService extends AbstractExecutorService
    implements ListeningScheduledExecutorService {