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/*******************************************************************************
* Copyright (c) 2003, 2005 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.osgi.framework.internal.core;
import java.net.URL;
import java.util.Enumeration;
import org.eclipse.osgi.framework.util.KeyedHashSet;
/**
* 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 KeyedHashSet sources;
private NullPackageSource(String name) {
super(name);
}
public SingleSourcePackage[] getSuppliers() {
return null;
}
public boolean isNullSource() {
return true;
}
public String toString() {
return id + " -> null"; //$NON-NLS-1$
}
public Class loadClass(String name) {
return null;
}
public URL getResource(String name) {
return null;
}
public Enumeration getResources(String name) {
return null;
}
public static synchronized NullPackageSource getNullPackageSource(String name) {
if (sources == null)
sources = new KeyedHashSet();
NullPackageSource result = (NullPackageSource) sources.getByKey(name);
if (result != null)
return result;
result = new NullPackageSource(name);
sources.add(result);
return result;
}
}
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