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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 -*-
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

// API class

package org.mozilla.javascript;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Method;

public abstract class VMBridge {

    static final VMBridge instance = makeInstance();

    private static VMBridge makeInstance() {
        String[] classNames = {
            "org.mozilla.javascript.VMBridge_custom", "org.mozilla.javascript.jdk18.VMBridge_jdk18",
        };
        for (int i = 0; i != classNames.length; ++i) {
            String className = classNames[i];
            Class cl = Kit.classOrNull(className);
            if (cl != null) {
                VMBridge bridge = (VMBridge) Kit.newInstanceOrNull(cl);
                if (bridge != null) {
                    return bridge;
                }
            }
        }
        throw new IllegalStateException("Failed to create VMBridge instance");
    }

    /**
     * Return a helper object to optimize {@link Context} access.
     *
     * The runtime will pass the resulting helper object to the subsequent calls to {@link
     * #getContext(Object contextHelper)} and {@link #setContext(Object contextHelper, Context cx)}
     * methods. In this way the implementation can use the helper to cache information about current
     * thread to make {@link Context} access faster.
     */
    protected abstract Object getThreadContextHelper();

    /**
     * Get {@link Context} instance associated with the current thread or null if none.
     *
     * @param contextHelper The result of {@link #getThreadContextHelper()} called from the current
     *     thread.
     */
    protected abstract Context getContext(Object contextHelper);

    /**
     * Associate {@link Context} instance with the current thread or remove the current association
     * if cx is null.
     *
     * @param contextHelper The result of {@link #getThreadContextHelper()} called from the current
     *     thread.
     */
    protected abstract void setContext(Object contextHelper, Context cx);

    /**
     * In many JVMSs, public methods in private classes are not accessible by default (Sun Bug
     * #4071593). VMBridge instance should try to workaround that via, for example, calling
     * method.setAccessible(true) when it is available. The implementation is responsible to catch
     * all possible exceptions like SecurityException if the workaround is not available.
     *
     * @return true if it was possible to make method accessible or false otherwise.
     */
    protected abstract boolean tryToMakeAccessible(AccessibleObject accessible);

    /**
     * Create helper object to create later proxies implementing the specified interfaces later.
     * Under JDK 1.3 the implementation can look like:
     *
     * 
     * return java.lang.reflect.Proxy.getProxyClass(..., interfaces).
     *     getConstructor(new Class[] {
     *         java.lang.reflect.InvocationHandler.class });
     * 
     *
     * @param interfaces Array with one or more interface class objects.
     */
    protected abstract Object getInterfaceProxyHelper(ContextFactory cf, Class[] interfaces);

    /**
     * Create proxy object for {@link InterfaceAdapter}. The proxy should call {@link
     * InterfaceAdapter#invoke(ContextFactory, Object, Scriptable, Object, Method, Object[])} as
     * implementation of interface methods associated with proxyHelper. {@link Method}
     *
     * @param proxyHelper The result of the previous call to {@link
     *     #getInterfaceProxyHelper(ContextFactory, Class[])}.
     */
    protected abstract Object newInterfaceProxy(
            Object proxyHelper,
            ContextFactory cf,
            InterfaceAdapter adapter,
            Object target,
            Scriptable topScope);
}