Copyright (c) 2003, 2014 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation
/*******************************************************************************
 * Copyright (c) 2003, 2014 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.osgi.internal.loader.sources;

import java.net.URL;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

This class is used to optimize finding provided-packages for a bundle.
If the package cannot be found in a list of required bundles then this class
is used to cache a null package source so that the search does not need to
be done again.
/**
 * This class is used to optimize finding provided-packages for a bundle.
 * If the package cannot be found in a list of required bundles then this class
 * is used to cache a null package source so that the search does not need to
 * be done again.
 */
public class NullPackageSource extends PackageSource {
	static Map<String, NullPackageSource> sources = new HashMap<>();

	private NullPackageSource(String name) {
		super(name);
	}

	@Override
	public SingleSourcePackage[] getSuppliers() {
		return null;
	}

	@Override
	public boolean isNullSource() {
		return true;
	}

	@Override
	public Class<?> loadClass(String name) {
		return null;
	}

	@Override
	public URL getResource(String name) {
		return null;
	}

	@Override
	public Enumeration<URL> getResources(String name) {
		return null;
	}

	public static synchronized NullPackageSource getNullPackageSource(String name) {
		NullPackageSource result = sources.get(name);
		if (result != null)
			return result;
		result = new NullPackageSource(name);
		sources.put(name, result);
		return result;
	}

	@Override
	public List<String> listResources(String path, String filePattern) {
		return Collections.<String> emptyList();
	}
}