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Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically embedded into Java applications to provide scripting to end users.
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/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1997-1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Bob Jervis
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License Version 2 or later (the "GPL"), in which
 * case the provisions of the GPL are applicable instead of those above. If
 * you wish to allow use of your version of this file only under the terms of
 * the GPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replacing
 * them with the notice and other provisions required by the GPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the GPL.
 *
 * ***** END LICENSE BLOCK ***** */

// API class

package org.mozilla.javascript;

public interface ConstProperties {
    /**
     * Sets a named const property in this object.
     * 
     * The property is specified by a string name
     * as defined for Scriptable.get.
     * 

     * The possible values that may be passed in are as defined for
     * Scriptable.get. A class that implements this method may choose
     * to ignore calls to set certain properties, in which case those
     * properties are effectively read-only.

     * For properties defined in a prototype chain,
     * use putProperty in ScriptableObject. 

     * Note that if a property a is defined in the prototype p
     * of an object o, then evaluating o.a = 23 will cause
     * set to be called on the prototype p with
     * o as the  start parameter.
     * To preserve JavaScript semantics, it is the Scriptable
     * object's responsibility to modify o. 

     * This design allows properties to be defined in prototypes and implemented
     * in terms of getters and setters of Java values without consuming slots
     * in each instance.

     * 

     * The values that may be set are limited to the following:
     * 

     * java.lang.Boolean objects
     * java.lang.String objects
     * java.lang.Number objects
     * org.mozilla.javascript.Scriptable objects
     * null
     * The value returned by Context.getUndefinedValue()
     * 

     * Arbitrary Java objects may be wrapped in a Scriptable by first calling
     * Context.toObject. This allows the property of a JavaScript
     * object to contain an arbitrary Java object as a value.
     * Note that has will be called by the runtime first before
     * set is called to determine in which object the
     * property is defined.
     * Note that this method is not expected to traverse the prototype chain,
     * which is different from the ECMA [[Put]] operation.
     * @param name the name of the property
     * @param start the object whose property is being set
     * @param value value to set the property to
     * @see org.mozilla.javascript.Scriptable#has
     * @see org.mozilla.javascript.Scriptable#get
     * @see org.mozilla.javascript.ScriptableObject#putProperty
     * @see org.mozilla.javascript.Context#toObject
     */
    public void putConst(String name, Scriptable start, Object value);

    /**
     * Reserves a definition spot for a const.  This will set up a definition
     * of the const property, but set its value to undefined.  The semantics of
     * the start parameter is the same as for putConst.
     * @param name The name of the property.
     * @param start The object whose property is being reserved.
     */
    public void defineConst(String name, Scriptable start);

    /**
     * Returns true if the named property is defined as a const on this object.
     * @param name
     * @return true if the named property is defined as a const, false
     * otherwise.
     */
    public boolean isConst(String name);
}