import com.google.common.collect.testing.features.MapFeature;
import java.util.Collection;
import java.util.Map.Entry;
import org.junit.Ignore;

/**
 * Tests {@link java.util.Map#hashCode}.
 *
 * @author George van den Driessche
 * @author Chris Povirk
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")

/**
 * A generic JUnit test which tests {@code remove} operations on a collection. Can't be invoked
 * directly; please see {@link com.google.common.collect.testing.CollectionTestSuiteBuilder}.
 *
 * @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 clear()} 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 org.junit.Ignore;

/**
 * A generic JUnit test which tests {@code clear()} 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")

 * Note that this means a test should not require more than one CollectionSize, since a particular
 * collection instance can only be one size at once.
 *
 * @author George van den Driessche
 */
@SuppressWarnings("rawtypes") // maybe avoidable if we rework the whole package?
@GwtCompatible
public enum CollectionSize implements Feature<Collection>, Comparable<CollectionSize> {

 * Note that this means a test should not require more than one CollectionSize, since a particular
 * collection instance can only be one size at once.
 *
 * @author George van den Driessche
 */
@SuppressWarnings("rawtypes") // maybe avoidable if we rework the whole package?
@GwtCompatible
public enum CollectionSize implements Feature<Collection>, Comparable<CollectionSize> {

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.

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.