new Target(MinimalCollection.of(e0(), e0(), e3(), e3()), "containsDuplicates");
    partialOverlap = new Target(MinimalCollection.of(e2(), e3()), "partialOverlap");
    nullSingleton = new Target(Collections.<E>singleton(null), "nullSingleton");
  }

  // retainAll(empty)

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ZERO)
  public void testRetainAll_emptyPreviouslyEmpty() {

   * Collections#emptyList}, and is preferable mainly for consistency and maintainability of your
   * code.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  // Casting to any type is safe because the list will never hold any elements.
  @SuppressWarnings("unchecked")
  public static <E> ImmutableList<E> of() {
    return (ImmutableList<E>) EMPTY;
  }

  /**

   * the JDK {@link java.util.function.Function} class, see {@link Function}.
   */
  public static Function<Object, String> toStringFunction() {
    return ToStringFunction.INSTANCE;
  }

  // enum singleton pattern
  private enum ToStringFunction implements Function<Object, String> {
    INSTANCE;

    @Override
    public String apply(Object o) {
      checkNotNull(o); // eager for GWT.
      return o.toString();

import static java.util.Arrays.asList;
import static java.util.Collections.emptyList;
import static java.util.Collections.emptySet;
import static java.util.Collections.nCopies;
import static java.util.Collections.singleton;
import static java.util.Collections.singletonList;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;

 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.maven.artifact.resolver;

import javax.inject.Inject;
import javax.inject.Named;
import javax.inject.Singleton;

import java.io.File;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;

import static java.util.Arrays.asList;
import static java.util.Collections.emptyList;
import static java.util.Collections.emptySet;
import static java.util.Collections.nCopies;
import static java.util.Collections.singleton;
import static java.util.Collections.singletonList;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;

    // ===================================================================================
    //                                                                           Singleton
    //                                                                           =========
    private static final FailureUrlDbm _instance = new FailureUrlDbm();

    private FailureUrlDbm() {
    }

  }

  /**
   * Returns a {@link Writer} that simply discards written chars.
   *
   * <p><b>Java 11+ users:</b> use {@link Writer#nullWriter()} instead. Note that the {@link
   * CharStreams} method returns a singleton writer whose {@code close} method has no effect, while
   * the {@link Writer#nullWriter()} method returns a new instance whose methods throw after the
   * instance is {@link Writer#close() closed}.
   *
   * @since 15.0

        // Add shutdown hook for cleanup
        Runtime.getRuntime().addShutdownHook(new Thread(this::shutdown, "ResourceManager-Shutdown"));

        startCleanupTask();
    }

    /**
     * Get the singleton instance
     *
     * @return ResourceManager instance
     */
    public static ResourceManager getInstance() {
        return INSTANCE;
    }

    /**
     * Register a resource for tracking

    // ===================================================================================
    //                                                                           Singleton
    //                                                                           =========
    private static final ElevateWordDbm _instance = new ElevateWordDbm();

    private ElevateWordDbm() {
    }