DefaultValueImpl.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
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 * 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,
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package jdk.nashorn.api.scripting;

import jdk.nashorn.internal.runtime.JSType;

/**
 * Default implementation of {@link JSObject#getDefaultValue(Class)}. Isolated into a separate class mostly so
 * that we can have private static instances of function name arrays, something we couldn't declare without it
 * being visible in {@link JSObject} interface.
 */
class DefaultValueImpl {
    private static final String[] DEFAULT_VALUE_FNS_NUMBER = new String[] { "valueOf", "toString" };
    private static final String[] DEFAULT_VALUE_FNS_STRING = new String[] { "toString", "valueOf" };

    static Object getDefaultValue(final JSObject jsobj, final Class<?> hint) throws UnsupportedOperationException {
        final boolean isNumber = hint == null || hint == Number.class;
        for(final String methodName: isNumber ? DEFAULT_VALUE_FNS_NUMBER : DEFAULT_VALUE_FNS_STRING) {
            final Object objMember = jsobj.getMember(methodName);
            if (objMember instanceof JSObject) {
                final JSObject member = (JSObject)objMember;
                if (member.isFunction()) {
                    final Object value = member.call(jsobj);
                    if (JSType.isPrimitive(value)) {
                        return value;
                    }
                }
            }
        }
        throw new UnsupportedOperationException(isNumber ? "cannot.get.default.number" : "cannot.get.default.string");
    }
}