my-jdk/jdkSrc/jdk8/sun/util/resources/OpenListResourceBundle.java

/*
 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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/*
 * (C) Copyright Taligent, Inc. 1996, 1997 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996 - 1998 - All Rights Reserved
 *
 * The original version of this source code and documentation
 * is copyrighted and owned by Taligent, Inc., a wholly-owned
 * subsidiary of IBM. These materials are provided under terms
 * of a License Agreement between Taligent and Sun. This technology
 * is protected by multiple US and International patents.
 *
 * This notice and attribution to Taligent may not be removed.
 * Taligent is a registered trademark of Taligent, Inc.
 *
 */

package sun.util.resources;

import java.util.Enumeration;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.ResourceBundle;
import java.util.Set;
import sun.util.ResourceBundleEnumeration;

/**
 * Subclass of <code>ResourceBundle</code> which mimics
 * <code>ListResourceBundle</code>, but provides more hooks
 * for specialized subclass behavior. For general description,
 * see {@link java.util.ListResourceBundle}.
 * <p>
 * This class leaves handleGetObject non-final, and
 * adds a method createMap which allows subclasses to
 * use specialized Map implementations.
 */
public abstract class OpenListResourceBundle extends ResourceBundle {
    /**
     * Sole constructor.  (For invocation by subclass constructors, typically
     * implicit.)
     */
    protected OpenListResourceBundle() {
    }

    // Implements java.util.ResourceBundle.handleGetObject; inherits javadoc specification.
    @Override
    protected Object handleGetObject(String key) {
        if (key == null) {
            throw new NullPointerException();
        }

        loadLookupTablesIfNecessary();
        return lookup.get(key); // this class ignores locales
    }

    /**
     * Implementation of ResourceBundle.getKeys.
     */
    @Override
    public Enumeration<String> getKeys() {
        ResourceBundle parentBundle = this.parent;
        return new ResourceBundleEnumeration(handleKeySet(),
                (parentBundle != null) ? parentBundle.getKeys() : null);
     }

    /**
     * Returns a set of keys provided in this resource bundle,
     * including no parents.
     */
    @Override
    protected Set<String> handleKeySet() {
        loadLookupTablesIfNecessary();
        return lookup.keySet();
    }

    @Override
    public Set<String> keySet() {
        if (keyset != null) {
            return keyset;
        }
        Set<String> ks = createSet();
        ks.addAll(handleKeySet());
        if (parent != null) {
            ks.addAll(parent.keySet());
        }
        synchronized (this) {
            if (keyset == null) {
                keyset = ks;
            }
        }
        return keyset;
    }

    /**
     * See ListResourceBundle class description.
     */
    abstract protected Object[][] getContents();

    /**
     * Load lookup tables if they haven't been loaded already.
     */
    void loadLookupTablesIfNecessary() {
        if (lookup == null) {
            loadLookup();
        }
    }

    /**
     * We lazily load the lookup hashtable.  This function does the
     * loading.
     */
    private void loadLookup() {
        Object[][] contents = getContents();
        Map<String, Object> temp = createMap(contents.length);
        for (int i = 0; i < contents.length; ++i) {
            // key must be non-null String, value must be non-null
            String key = (String) contents[i][0];
            Object value = contents[i][1];
            if (key == null || value == null) {
                throw new NullPointerException();
            }
            temp.put(key, value);
        }
        synchronized (this) {
            if (lookup == null) {
                lookup = temp;
            }
        }
    }

    /**
     * Lets subclasses provide specialized Map implementations.
     * Default uses HashMap.
     */
    protected <K, V> Map<K, V> createMap(int size) {
        return new HashMap<>(size);
    }

    protected <E> Set<E> createSet() {
        return new HashSet<>();
    }

    private volatile Map<String, Object> lookup = null;
    private volatile Set<String> keyset;
}