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API module of JSR 374:Java API for Processing JSON
There is a newer version: 1.1.4
/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 2017 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://oss.oracle.com/licenses/CDDL+GPL-1.1
 * or LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
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 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
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 */

package javax.json;

import java.io.Serializable;
import java.util.AbstractMap;
import java.util.Collections;
import java.util.Set;

/**
 * Private implementation of immutable {@link JsonObject}.
 *
 * @author Lukas Jungmann
 */
final class EmptyObject extends AbstractMap implements JsonObject, Serializable {

    private static final long serialVersionUID = -1461653546889072583L;

    @Override
    public Set> entrySet() {
        return Collections.>emptySet();
    }

    @Override
    public JsonArray getJsonArray(String name) {
        return (JsonArray) get(name);
    }

    @Override
    public JsonObject getJsonObject(String name) {
        return (JsonObject) get(name);
    }

    @Override
    public JsonNumber getJsonNumber(String name) {
        return (JsonNumber) get(name);
    }

    @Override
    public JsonString getJsonString(String name) {
        return (JsonString) get(name);
    }

    @Override
    public String getString(String name) {
        return getJsonString(name).getString();
    }

    @Override
    public String getString(String name, String defaultValue) {
        return defaultValue;
    }

    @Override
    public int getInt(String name) {
        return getJsonNumber(name).intValue();
    }

    @Override
    public int getInt(String name, int defaultValue) {
        return defaultValue;
    }

    @Override
    public boolean getBoolean(String name) {
        throw new NullPointerException();
    }

    @Override
    public boolean getBoolean(String name, boolean defaultValue) {
        return defaultValue;
    }

    @Override
    public boolean isNull(String name) {
        throw new NullPointerException();
    }

    @Override
    public ValueType getValueType() {
        return ValueType.OBJECT;
    }

    // Preserves singleton property
    private Object readResolve() {
        return JsonValue.EMPTY_JSON_OBJECT;
    }
}