* 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();

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

    private LabelTypeDbm() {
    }

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

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

import java.io.IOException;
import java.net.ConnectException;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.IdentityHashMap;

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

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.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

            }
        }
        return projects;
    }

    /**
     * Singleton class used to receive events by implementing the EventSpy.
     * It simply forwards all {@code ExecutionEvent}s to the {@code ReactorReader}.
     */
    @Named
    @Singleton
    @SuppressWarnings("unused")
    static class ReactorReaderSpy implements EventSpy {

        private final Lookup lookup;

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

    private FailureUrlDbm() {
    }

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

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

import java.io.File;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Properties;

import org.apache.maven.artifact.Artifact;

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

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

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

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

    private RequestHeaderDbm() {
    }

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

    private WebAuthenticationDbm() {
    }