Copyright (c) 2000, 2015 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
    Andrey Loskutov  - bug 484014
/*******************************************************************************
 * Copyright (c) 2000, 2015 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
 *     Andrey Loskutov <loskutov@gmx.de> - bug 484014
 *******************************************************************************/
package org.eclipse.core.internal.registry;

import java.lang.ref.SoftReference;
import org.eclipse.core.runtime.IContributor;

An object which represents the user-defined extension in a plug-in manifest.
/**
 * An object which represents the user-defined extension in a plug-in manifest.
 */
public class Extension extends RegistryObject {
	public static final Extension[] EMPTY_ARRAY = new Extension[0];

	//Extension simple identifier
	private String simpleId;
	//The namespace for the extension.
	private String namespaceIdentifier;

	//	Place holder for the label and  the extension point. It contains either a String[] or a SoftReference to a String[].
	//The array layout is [label, extension point name]
	private Object extraInformation;
	private static final byte LABEL = 0; //The human readable name of the extension
	private static final byte XPT_NAME = 1; // The fully qualified name of the extension point to which this extension is attached to
	private static final byte CONTRIBUTOR_ID = 2; // ID of the actual contributor of this extension
	private static final int EXTRA_SIZE = 3;

	protected Extension(ExtensionRegistry registry, boolean persist) {
		super(registry, persist);
	}

	protected Extension(int self, String simpleId, String namespace, int[] children, int extraData, ExtensionRegistry registry, boolean persist) {
		super(registry, persist);

		setObjectId(self);
		this.simpleId = simpleId;
		setRawChildren(children);
		setExtraDataOffset(extraData);
		this.namespaceIdentifier = namespace;
	}

	protected String getExtensionPointIdentifier() {
		String[] extraData = getExtraData();
		if (extraData == null) {
			return null;
		}
		return extraData[XPT_NAME];
	}

	protected String getSimpleIdentifier() {
		return simpleId;
	}

	protected String getUniqueIdentifier() {
		return simpleId == null ? null : this.getNamespaceIdentifier() + '.' + simpleId;
	}

	void setExtensionPointIdentifier(String value) {
		ensureExtraInformationType();
		((String[]) extraInformation)[XPT_NAME] = value;
	}

	void setSimpleIdentifier(String value) {
		simpleId = value;
	}

	private String[] getExtraData() {
		//The extension has been created by parsing, or does not have any extra data
		if (noExtraData()) {
			if (extraInformation != null)
				return (String[]) extraInformation;
			return null;
		}

		//The extension has been loaded from the cache.
		String[] result = null;
		if (extraInformation == null || (result = ((extraInformation instanceof SoftReference) ? (String[]) ((SoftReference<?>) extraInformation).get() : (String[]) extraInformation)) == null) {
			result = registry.getTableReader().loadExtensionExtraData(getExtraDataOffset());
			extraInformation = new SoftReference<>(result);
		}
		return result;
	}

	String getLabel() {
		String s = getExtraData()[LABEL];
		if (s == null)
			return ""; //$NON-NLS-1$
		return s;
	}

	void setLabel(String value) {
		ensureExtraInformationType();
		((String[]) extraInformation)[LABEL] = value;
	}

	String getContributorId() {
		String s = getExtraData()[CONTRIBUTOR_ID];
		if (s == null)
			return ""; //$NON-NLS-1$
		return s;
	}

	public IContributor getContributor() {
		return registry.getObjectManager().getContributor(getContributorId());
	}

	void setContributorId(String value) {
		ensureExtraInformationType();
		((String[]) extraInformation)[CONTRIBUTOR_ID] = value;
	}

	public String getNamespaceIdentifier() {
		return namespaceIdentifier;
	}

	void setNamespaceIdentifier(String value) {
		namespaceIdentifier = value;
	}

	@Override
	public String toString() {
		return getUniqueIdentifier() + " -> " + getExtensionPointIdentifier(); //$NON-NLS-1$
	}

	
At the end of this method, extra information will be a string[]
/**
	 * At the end of this method, extra information will be a string[]
	 */
	private void ensureExtraInformationType() {
		if (extraInformation instanceof SoftReference) {
			extraInformation = ((SoftReference<?>) extraInformation).get();
		}
		if (extraInformation == null) {
			extraInformation = new String[EXTRA_SIZE];
		}
	}

	String getLabelAsIs() {
		String s = getExtraData()[LABEL];
		if (s == null)
			return ""; //$NON-NLS-1$
		return s;
	}

	String getLabel(String locale) {
		registry.logMultiLangError();
		return getLabel();
	}

}