@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class AbstractIterator<T extends @Nullable Object> extends UnmodifiableIterator<T> {
  private State state = State.NOT_READY;

  /** Constructor for use by subclasses. */
  protected AbstractIterator() {}

  private enum State {
    /** We have computed the next element and haven't returned it yet. */
    READY,

      @SuppressWarnings("unchecked")
      @Override
      <K extends K0, V extends @Nullable Object> Map<K, Collection<V>> createMap() {
        // K must actually be K0, since enums are effectively final
        // (their subclasses are inaccessible)
        return (Map<K, Collection<V>>) new EnumMap<K0, Collection<V>>(keyClass);
      }
    };
  }

  private static final class ArrayListSupplier<V extends @Nullable Object>

   *     invocation conversion.
   * @throws InvocationTargetException if the underlying method or constructor throws an exception.
   */
  // All subclasses are owned by us and we'll make sure to get the R type right, including nullness.
  @SuppressWarnings({"unchecked", "nullness"})
  @CanIgnoreReturnValue
  @CheckForNull

 * class. For example, testing that {@code nodes()} method returns the set of the nodes in the
 * graph. The following test cases are left for the subclasses to handle:
 *
 * <ul>
 *   <li>Test cases related to whether the graph is directed, undirected, mutable, or immutable.
 *   <li>Test cases related to the specific implementation of the {@link Network} interface.
 * </ul>

 * </ul>
 *
 * @since 14.0
 * @author Colin Decker
 */
@J2ktIncompatible
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public abstract class CharSource {

  /** Constructor for use by subclasses. */
  protected CharSource() {}

  /**
   * Returns a {@link ByteSource} view of this char source that encodes chars read from this source
   * as bytes using the given {@link Charset}.
   *

/**
 * Helper classes for various benchmarks.
 *
 * @author Christopher Swenson
 */
final class BenchmarkHelpers {
  /** So far, this is the best way to test various implementations of {@link Set} subclasses. */
  public interface CollectionsImplEnum {
    <E extends Comparable<E>> Collection<E> create(Collection<E> contents);

    String name();
  }

  public interface MapsImplEnum {

import java.util.concurrent.TimeoutException;
import junit.framework.TestCase;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Base class for tests for emulated {@link AbstractFuture} that allow subclasses to swap in a
 * different "source Future" for {@link AbstractFuture#setFuture} calls.
 */
@GwtCompatible(emulated = true)
abstract class AbstractAbstractFutureTest extends TestCase {
  private TestedFuture<Integer> future;

 *
 * <p>{@link #setDefault} allows subclasses to specify default values for types.
 *
 * <p>This class incurs IO because it scans the classpath and reads classpath resources.
 *
 * @author Ben Yu
 * @since 14.0
 */
// TODO: Switch to JUnit 4 and use @Parameterized and @BeforeClass
// Note: @Test annotations are deliberate, as some subclasses specify @RunWith(JUnit4).
@GwtIncompatible
@J2ktIncompatible

      } catch (ClassCastException wastNotComparableToOurType) {
        return false;
      }
    }
    return false;
  }

  // Prevent "missing hashCode" warning by explicitly forcing subclasses implement it
  @Override
  public abstract int hashCode();

  /*
   * The implementation neither produces nor consumes any non-null instance of type C, so
   * casting the type parameter is safe.
   */

Nós poderíamos fazer melhor.

Podemos declarar um modelo `UserBase` que serve como base para nossos outros modelos. E então podemos fazer subclasses desse modelo que herdam seus atributos (declarações de tipo, validação, etc.).

Toda conversão de dados, validação, documentação, etc. ainda funcionará normalmente.