/*
 * 
 * Copyright 2004 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * The contents of this file are subject to the Sun Community Source
 * License v3.0/Jini Technology Specific Attachment v 1.0 (the
 * "License"). You may not use this file except in compliance with the
 * License. You may obtain a copy of the License at
 * http://wwws.sun.com/software/jini/licensing/SCSL3_JiniTSA1.html.
 * Software distributed under the License is distributed on an "AS IS"
 * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
 * the License for the specific language governing rights and limitations
 * under the License.
 * 
 * The Reference Code is Jini Technology Core Platform code, v2.0. The
 * Developer of the Reference Code is Sun Microsystems, Inc.
 * 
 * Contributor(s): Sun Microsystems, Inc.
 * 
 * The contents of this file comply with the Jini Technology Core
 * Platform Compatibility Kit, v2.0A.
 * 
 * Tester(s): Sun Microsystems, Inc.
 * 
 * Test Platform(s):
 * Java 2 SDK, Standard Edition, Version 1.4.2_03 for Solaris(TM)SPARC/x86
 * Java 2 SDK, Standard Edition, Version 1.4.2_03 for Linux (Intel x86)
 * Java 2 SDK, Standard Edition, Version 1.4.2_03 for Windows (Intel Platform)
 * 
 */

package net.jini.config;

import com.sun.jini.logging.Levels;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * A <code>Configuration</code> with no entries. Applications can use an
 * instance of this class to simplify handling cases where no configuration is
 * specified rather than, for example, checking for a <code>null</code>
 * configuration.
 *
 * @author Sun Microsystems, Inc.
 * @since 2.0
 *
 * @com.sun.jini.impl <!-- Implementation Specifics -->
 *
 * This implementation uses the {@link Logger} named
 * <code>net.jini.config</code> to log information at the following logging
 * levels: <p>
 *
 * <table border="1" cellpadding="5" summary="Describes logging performed by
 *	  the EmptyConfiguration class at different logging levels">
 *
 * <caption halign="center" valign="top"><b><code>
 *	    net.jini.config</code></b></caption>
 *
 * <tr> <th scope="col"> Level <th scope="col"> Description
 *
 * <tr> <td> {@link Levels#FAILED FAILED} <td> problems getting entries,
 *	including getting entries that are not found
 *
 * <tr> <td> {@link Level#FINE FINE} <td> returning default values
 *
 * </table>
 */
public class EmptyConfiguration extends AbstractConfiguration {

    /** A <code>Configuration</code> with no entries. */
    public static final EmptyConfiguration INSTANCE = new EmptyConfiguration();

    /* Insure there is only one instance */
    private EmptyConfiguration() { }

    /**
     * Always throws an exception -- this configuration contains no entries.
     *
     * @throws NullPointerException {@inheritDoc}
     * @throws NoSuchEntryException unless <code>component</code>,
     * <code>name</code>, or <code>type</code> is <code>null</code>
     */
    protected Object getEntryInternal(
	String component, String name, Class type, Object data)
	throws NoSuchEntryException
    {
	if (component == null || name == null || type == null) {
	    throw new NullPointerException(
		"component, name and type cannot be null");
	}
	throw new NoSuchEntryException(
	    "Entry not found for component " + component + ", name " + name);
    }
}
