import com.google.common.util.concurrent.ListenableFutureTask;
import java.io.Serializable;
import java.util.Map;
import java.util.concurrent.Executor;

/**
 * Computes or retrieves values, based on a key, for use in populating a {@link LoadingCache}.
 *
 * <p>Most implementations will only need to implement {@link #load}. Other methods may be
 * overridden as desired.
 *
 * <p>Usage example:
 *

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * This class provides a skeletal implementation of the {@link ListIterator} interface across a
 * fixed number of elements that may be retrieved by position. It does not support {@link #remove},
 * {@link #set}, or {@link #add}.
 *
 * @author Jared Levy
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * This class provides a skeletal implementation of the {@link ListIterator} interface across a
 * fixed number of elements that may be retrieved by position. It does not support {@link #remove},
 * {@link #set}, or {@link #add}.
 *
 * @author Jared Levy
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault

import com.google.common.util.concurrent.ListenableFutureTask;
import java.io.Serializable;
import java.util.Map;
import java.util.concurrent.Executor;

/**
 * Computes or retrieves values, based on a key, for use in populating a {@link LoadingCache}.
 *
 * <p>Most implementations will only need to implement {@link #load}. Other methods may be
 * overridden as desired.
 *
 * <p>Usage example:
 *

    }
  }

  public void testBroken() {
    Iterator<Object> broken = new BrokenAbstractSequentialIterator();
    assertTrue(broken.hasNext());
    // We can't retrieve even the known first element:
    try {
      broken.next();
      fail();
    } catch (MyException expected) {
    }
    try {
      broken.next();
      fail();
    } catch (MyException expected) {

 * with any other implementation of this interface.
 *
 * <p>If you have your own graph implementation based around a custom node type {@code MyNode},
 * which has a method {@code getParents()} that retrieves its predecessors in a graph:
 *
 * <pre>{@code
 * someGraphAlgorithm(startNode, MyNode::getParents);
 * }</pre>
 *
 * <p>If you have some other mechanism for returning the predecessors of a node, or one that doesn't

 * any other implementation of this interface.
 *
 * <p>If you have your own graph implementation based around a custom node type {@code MyNode},
 * which has a method {@code getChildren()} that retrieves its successors in a graph:
 *
 * <pre>{@code
 * someGraphAlgorithm(startNode, MyNode::getChildren);
 * }</pre>
 *
 * <p>If you have some other mechanism for returning the successors of a node, or one that doesn't

 *
 * @author Harry Heymann
 * @since 2.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public interface Supplier<T extends @Nullable Object>
{
  /**
   * Retrieves an instance of the appropriate type. The returned object may or may not be a new
   * instance, depending on the implementation.
   *
   * @return an instance of the appropriate type
   */
  @ParametricNullness

    }
  }

  public void testBroken() {
    Iterator<Object> broken = new BrokenAbstractSequentialIterator();
    assertTrue(broken.hasNext());
    // We can't retrieve even the known first element:
    try {
      broken.next();
      fail();
    } catch (MyException expected) {
    }
    try {
      broken.next();
      fail();
    } catch (MyException expected) {

 * such as {@link java.io.Reader#read()}, do not expose this information; the only way to discover
 * whether there is any data left is by trying to retrieve it. These types of data sources are
 * ordinarily difficult to write iterators for. But using this class, one must implement only the
 * {@link #computeNext} method, and invoke the {@link #endOfData} method when appropriate.
 *