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 * Copyright (c) 2008, 2018, 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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package java.lang.invoke;

import jdk.internal.misc.SharedSecrets;

import jdk.internal.module.IllegalAccessLogger;

import jdk.internal.org.objectweb.asm.ClassReader;

import jdk.internal.reflect.CallerSensitive;

import jdk.internal.reflect.Reflection;

import jdk.internal.vm.annotation.ForceInline;

import sun.invoke.util.ValueConversions;

import sun.invoke.util.VerifyAccess;

import sun.invoke.util.Wrapper;

import sun.reflect.misc.ReflectUtil;

import sun.security.util.SecurityConstants;

import java.lang.invoke.LambdaForm.BasicType;

import java.lang.reflect.Constructor;

import java.lang.reflect.Field;

import java.lang.reflect.Member;

import java.lang.reflect.Method;

import java.lang.reflect.Modifier;

import java.lang.reflect.ReflectPermission;

import java.nio.ByteOrder;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.security.ProtectionDomain;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.BitSet;

import java.util.Iterator;

import java.util.List;

import java.util.Objects;

import java.util.concurrent.ConcurrentHashMap;

import java.util.stream.Collectors;

import java.util.stream.Stream;

import static java.lang.invoke.MethodHandleImpl.Intrinsic;

import static java.lang.invoke.MethodHandleNatives.Constants.*;

import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;

import static java.lang.invoke.MethodType.methodType;

/**

 * This class consists exclusively of static methods that operate on or return

 * method handles. They fall into several categories:

 * <ul>

 * <li>Lookup methods which help create method handles for methods and fields.

 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.

 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.

 * </ul>

 *

 * @author John Rose, JSR 292 EG

 * @since 1.7

 */

public class MethodHandles {

    private MethodHandles() { }  // do not instantiate

    static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();

    // See IMPL_LOOKUP below.

    //// Method handle creation from ordinary methods.

    /**

     * Returns a {@link Lookup lookup object} with

     * full capabilities to emulate all supported bytecode behaviors of the caller.

     * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.

     * Factory methods on the lookup object can create

     * <a href="MethodHandleInfo.html#directmh">direct method handles</a>

     * for any member that the caller has access to via bytecodes,

     * including protected and private fields and methods.

     * This lookup object is a <em>capability</em> which may be delegated to trusted agents.

     * Do not store it in place where untrusted code can access it.

     * <p>

     * This method is caller sensitive, which means that it may return different

     * values to different callers.

     * @return a lookup object for the caller of this method, with private access

     */

    @CallerSensitive

    @ForceInline // to ensure Reflection.getCallerClass optimization

    public static Lookup lookup() {

        return new Lookup(Reflection.getCallerClass());

    }

    /**

     * This reflected$lookup method is the alternate implementation of

     * the lookup method when being invoked by reflection.

     */

    @CallerSensitive

    private static Lookup reflected$lookup() {

        Class<?> caller = Reflection.getCallerClass();

        if (caller.getClassLoader() == null) {

            throw newIllegalArgumentException("illegal lookupClass: "+caller);

        }

        return new Lookup(caller);

    }

    /**

     * Returns a {@link Lookup lookup object} which is trusted minimally.

     * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.

     * It can only be used to create method handles to public members of

     * public classes in packages that are exported unconditionally.

     * <p>

     * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}

     * of this lookup object will be {@link java.lang.Object}.

     *

     * @apiNote The use of Object is conventional, and because the lookup modes are

     * limited, there is no special access provided to the internals of Object, its package

     * or its module. Consequently, the lookup context of this lookup object will be the

     * bootstrap class loader, which means it cannot find user classes.

     *

     * <p style="font-size:smaller;">

     * <em>Discussion:</em>

     * The lookup class can be changed to any other class {@code C} using an expression of the form

     * {@link Lookup#in publicLookup().in(C.class)}.

     * but may change the lookup context by virtue of changing the class loader.

     * A public lookup object is always subject to

     * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.

     * Also, it cannot access

     * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.

     * @return a lookup object which is trusted minimally

     *

     * @revised 9

     * @spec JPMS

     */

    public static Lookup publicLookup() {

        return Lookup.PUBLIC_LOOKUP;

    }

    /**

     * Returns a {@link Lookup lookup object} with full capabilities to emulate all

     * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">

     * private access</a>, on a target class.

     * This method checks that a caller, specified as a {@code Lookup} object, is allowed to

     * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing

     * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing

     * the target class, then this check ensures that

     * <ul>

     *     <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>

     *     <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing

     *     the target class to at least {@code m1}.</li>

     *     <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>

     * </ul>

     * <p>

     * If there is a security manager, its {@code checkPermission} method is called to

     * check {@code ReflectPermission("suppressAccessChecks")}.

     * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object

     * was created by code in the caller module (or derived from a lookup object originally

     * created by the caller). A lookup object with the {@code MODULE} lookup mode can be

     * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}

     * access to the caller.

     * @param targetClass the target class

     * @param lookup the caller lookup object

     * @return a lookup object for the target class, with private access

     * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class

     * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}

     * @throws IllegalAccessException if the access check specified above fails

     * @throws SecurityException if denied by the security manager

     * @since 9

     * @spec JPMS

     * @see Lookup#dropLookupMode

     */

    public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) sm.checkPermission(ACCESS_PERMISSION);

        if (targetClass.isPrimitive())

            throw new IllegalArgumentException(targetClass + " is a primitive class");

        if (targetClass.isArray())

            throw new IllegalArgumentException(targetClass + " is an array class");

        Module targetModule = targetClass.getModule();

        Module callerModule = lookup.lookupClass().getModule();

        if (!callerModule.canRead(targetModule))

            throw new IllegalAccessException(callerModule + " does not read " + targetModule);

        if (targetModule.isNamed()) {

            String pn = targetClass.getPackageName();

            assert pn.length() > 0 : "unnamed package cannot be in named module";

            if (!targetModule.isOpen(pn, callerModule))

                throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);

        }

        if ((lookup.lookupModes() & Lookup.MODULE) == 0)

            throw new IllegalAccessException("lookup does not have MODULE lookup mode");

        if (!callerModule.isNamed() && targetModule.isNamed()) {

            IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();

            if (logger != null) {

                logger.logIfOpenedForIllegalAccess(lookup, targetClass);

            }

        }

        return new Lookup(targetClass);

    }

    /**

     * Performs an unchecked "crack" of a

     * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.

     * The result is as if the user had obtained a lookup object capable enough

     * to crack the target method handle, called

     * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}

     * on the target to obtain its symbolic reference, and then called

     * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}

     * to resolve the symbolic reference to a member.

     * <p>

     * If there is a security manager, its {@code checkPermission} method

     * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.

     * @param <T> the desired type of the result, either {@link Member} or a subtype

     * @param target a direct method handle to crack into symbolic reference components

     * @param expected a class object representing the desired result type {@code T}

     * @return a reference to the method, constructor, or field object

     * @exception SecurityException if the caller is not privileged to call {@code setAccessible}

     * @exception NullPointerException if either argument is {@code null}

     * @exception IllegalArgumentException if the target is not a direct method handle

     * @exception ClassCastException if the member is not of the expected type

     * @since 1.8

     */

    public static <T extends Member> T

    reflectAs(Class<T> expected, MethodHandle target) {

        SecurityManager smgr = System.getSecurityManager();

        if (smgr != null)  smgr.checkPermission(ACCESS_PERMISSION);

        Lookup lookup = Lookup.IMPL_LOOKUP;  // use maximally privileged lookup

        return lookup.revealDirect(target).reflectAs(expected, lookup);

    }

    // Copied from AccessibleObject, as used by Method.setAccessible, etc.:

    private static final java.security.Permission ACCESS_PERMISSION =

        new ReflectPermission("suppressAccessChecks");

    /**

     * A <em>lookup object</em> is a factory for creating method handles,

     * when the creation requires access checking.

     * Method handles do not perform

     * access checks when they are called, but rather when they are created.

     * Therefore, method handle access

     * restrictions must be enforced when a method handle is created.

     * The caller class against which those restrictions are enforced

     * is known as the {@linkplain #lookupClass() lookup class}.

     * <p>

     * A lookup class which needs to create method handles will call

     * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.

     * When the {@code Lookup} factory object is created, the identity of the lookup class is

     * determined, and securely stored in the {@code Lookup} object.

     * The lookup class (or its delegates) may then use factory methods

     * on the {@code Lookup} object to create method handles for access-checked members.

     * This includes all methods, constructors, and fields which are allowed to the lookup class,

     * even private ones.

     *

     * <h1><a id="lookups"></a>Lookup Factory Methods</h1>

     * The factory methods on a {@code Lookup} object correspond to all major

     * use cases for methods, constructors, and fields.

     * Each method handle created by a factory method is the functional

     * equivalent of a particular <em>bytecode behavior</em>.

     * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)

     * Here is a summary of the correspondence between these factory methods and

     * the behavior of the resulting method handles:

     * <table class="striped">

     * <caption style="display:none">lookup method behaviors</caption>

     * <thead>

     * <tr>

     *     <th scope="col"><a id="equiv"></a>lookup expression</th>

     *     <th scope="col">member</th>

     *     <th scope="col">bytecode behavior</th>

     * </tr>

     * </thead>

     * <tbody>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>

     *     <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>

     *     <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>

     *     <td>{@code FT f;}</td><td>{@code this.f = x;}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>

     *     <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>

     *     <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>

     *     <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>

     *     <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>

     *     <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>

     *     <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>

     *     <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>

     *     <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>

     *     <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>

     *     <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>

     * </tr>

     * <tr>

     *     <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>

     *     <td>{@code class C { ... }}</td><td>{@code C.class;}</td>

     * </tr>

     * </tbody>

     * </table>

     *

     * Here, the type {@code C} is the class or interface being searched for a member,

     * documented as a parameter named {@code refc} in the lookup methods.

     * The method type {@code MT} is composed from the return type {@code T}

     * and the sequence of argument types {@code A*}.

     * The constructor also has a sequence of argument types {@code A*} and

     * is deemed to return the newly-created object of type {@code C}.

     * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.

     * The formal parameter {@code this} stands for the self-reference of type {@code C};

     * if it is present, it is always the leading argument to the method handle invocation.

     * (In the case of some {@code protected} members, {@code this} may be

     * restricted in type to the lookup class; see below.)

     * The name {@code arg} stands for all the other method handle arguments.

     * In the code examples for the Core Reflection API, the name {@code thisOrNull}

     * stands for a null reference if the accessed method or field is static,

     * and {@code this} otherwise.

     * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand

     * for reflective objects corresponding to the given members.

     * <p>

     * The bytecode behavior for a {@code findClass} operation is a load of a constant class,

     * as if by {@code ldc CONSTANT_Class}.

     * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.

     * <p>

     * In cases where the given member is of variable arity (i.e., a method or constructor)

     * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.

     * In all other cases, the returned method handle will be of fixed arity.

     * <p style="font-size:smaller;">

     * <em>Discussion:</em>

     * The equivalence between looked-up method handles and underlying

     * class members and bytecode behaviors

     * can break down in a few ways:

     * <ul style="font-size:smaller;">

     * <li>If {@code C} is not symbolically accessible from the lookup class's loader,

     * the lookup can still succeed, even when there is no equivalent

     * Java expression or bytecoded constant.

     * <li>Likewise, if {@code T} or {@code MT}

     * is not symbolically accessible from the lookup class's loader,

     * the lookup can still succeed.

     * For example, lookups for {@code MethodHandle.invokeExact} and

     * {@code MethodHandle.invoke} will always succeed, regardless of requested type.

     * <li>If there is a security manager installed, it can forbid the lookup

     * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).

     * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}

     * constant is not subject to security manager checks.

     * <li>If the looked-up method has a

     * <a href="MethodHandle.html#maxarity">very large arity</a>,

     * the method handle creation may fail, due to the method handle

     * type having too many parameters.

     * </ul>

     *

     * <h1><a id="access"></a>Access checking</h1>

     * Access checks are applied in the factory methods of {@code Lookup},

     * when a method handle is created.

     * This is a key difference from the Core Reflection API, since

     * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}

     * performs access checking against every caller, on every call.

     * <p>

     * All access checks start from a {@code Lookup} object, which

     * compares its recorded lookup class against all requests to

     * create method handles.

     * A single {@code Lookup} object can be used to create any number

     * of access-checked method handles, all checked against a single

     * lookup class.

     * <p>

     * A {@code Lookup} object can be shared with other trusted code,

     * such as a metaobject protocol.

     * A shared {@code Lookup} object delegates the capability

     * to create method handles on private members of the lookup class.

     * Even if privileged code uses the {@code Lookup} object,

     * the access checking is confined to the privileges of the

     * original lookup class.

     * <p>

     * A lookup can fail, because

     * the containing class is not accessible to the lookup class, or

     * because the desired class member is missing, or because the

     * desired class member is not accessible to the lookup class, or

     * because the lookup object is not trusted enough to access the member.

     * In any of these cases, a {@code ReflectiveOperationException} will be

     * thrown from the attempted lookup.  The exact class will be one of

     * the following:

     * <ul>

     * <li>NoSuchMethodException &mdash; if a method is requested but does not exist

     * <li>NoSuchFieldException &mdash; if a field is requested but does not exist

     * <li>IllegalAccessException &mdash; if the member exists but an access check fails

     * </ul>

     * <p>

     * In general, the conditions under which a method handle may be

     * looked up for a method {@code M} are no more restrictive than the conditions

     * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.

     * Where the JVM would raise exceptions like {@code NoSuchMethodError},

     * a method handle lookup will generally raise a corresponding

     * checked exception, such as {@code NoSuchMethodException}.

     * And the effect of invoking the method handle resulting from the lookup

     * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>

     * to executing the compiled, verified, and resolved call to {@code M}.

     * The same point is true of fields and constructors.

     * <p style="font-size:smaller;">

     * <em>Discussion:</em>

     * Access checks only apply to named and reflected methods,

     * constructors, and fields.

     * Other method handle creation methods, such as

     * {@link MethodHandle#asType MethodHandle.asType},

     * do not require any access checks, and are used

     * independently of any {@code Lookup} object.

     * <p>

     * If the desired member is {@code protected}, the usual JVM rules apply,

     * including the requirement that the lookup class must be either be in the

     * same package as the desired member, or must inherit that member.

     * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)

     * In addition, if the desired member is a non-static field or method

     * in a different package, the resulting method handle may only be applied

     * to objects of the lookup class or one of its subclasses.

     * This requirement is enforced by narrowing the type of the leading

     * {@code this} parameter from {@code C}

     * (which will necessarily be a superclass of the lookup class)

     * to the lookup class itself.

     * <p>

     * The JVM imposes a similar requirement on {@code invokespecial} instruction,

     * that the receiver argument must match both the resolved method <em>and</em>

     * the current class.  Again, this requirement is enforced by narrowing the

     * type of the leading parameter to the resulting method handle.

     * (See the Java Virtual Machine Specification, section 4.10.1.9.)

     * <p>

     * The JVM represents constructors and static initializer blocks as internal methods

     * with special names ({@code "<init>"} and {@code "<clinit>"}).

     * The internal syntax of invocation instructions allows them to refer to such internal

     * methods as if they were normal methods, but the JVM bytecode verifier rejects them.

     * A lookup of such an internal method will produce a {@code NoSuchMethodException}.

     * <p>

     * If the relationship between nested types is expressed directly through the

     * {@code NestHost} and {@code NestMembers} attributes

     * (see the Java Virtual Machine Specification, sections 4.7.28 and 4.7.29),

     * then the associated {@code Lookup} object provides direct access to

     * the lookup class and all of its nestmates

     * (see {@link java.lang.Class#getNestHost Class.getNestHost}).

     * Otherwise, access between nested classes is obtained by the Java compiler creating

     * a wrapper method to access a private method of another class in the same nest.

     * For example, a nested class {@code C.D}

     * can access private members within other related classes such as

     * {@code C}, {@code C.D.E}, or {@code C.B},

     * but the Java compiler may need to generate wrapper methods in

     * those related classes.  In such cases, a {@code Lookup} object on

     * {@code C.E} would be unable to access those private members.

     * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,

     * which can transform a lookup on {@code C.E} into one on any of those other

     * classes, without special elevation of privilege.

     * <p>

     * The accesses permitted to a given lookup object may be limited,

     * according to its set of {@link #lookupModes lookupModes},

     * to a subset of members normally accessible to the lookup class.

     * For example, the {@link MethodHandles#publicLookup publicLookup}

     * method produces a lookup object which is only allowed to access

     * public members in public classes of exported packages.

     * The caller sensitive method {@link MethodHandles#lookup lookup}

     * produces a lookup object with full capabilities relative to

     * its caller class, to emulate all supported bytecode behaviors.

     * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object

     * with fewer access modes than the original lookup object.

     *

     * <p style="font-size:smaller;">

     * <a id="privacc"></a>

     * <em>Discussion of private access:</em>

     * We say that a lookup has <em>private access</em>

     * if its {@linkplain #lookupModes lookup modes}

     * include the possibility of accessing {@code private} members

     * (which includes the private members of nestmates).

     * As documented in the relevant methods elsewhere,

     * only lookups with private access possess the following capabilities:

     * <ul style="font-size:smaller;">

     * <li>access private fields, methods, and constructors of the lookup class and its nestmates

     * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,

     *     such as {@code Class.forName}

     * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions

     * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>

     *     for classes accessible to the lookup class

     * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes

     *     within the same package member

     * </ul>

     * <p style="font-size:smaller;">

     * Each of these permissions is a consequence of the fact that a lookup object

     * with private access can be securely traced back to an originating class,

     * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions

     * can be reliably determined and emulated by method handles.

     *

     * <h1><a id="secmgr"></a>Security manager interactions</h1>

     * Although bytecode instructions can only refer to classes in

     * a related class loader, this API can search for methods in any

     * class, as long as a reference to its {@code Class} object is

     * available.  Such cross-loader references are also possible with the

     * Core Reflection API, and are impossible to bytecode instructions

     * such as {@code invokestatic} or {@code getfield}.

     * There is a {@linkplain java.lang.SecurityManager security manager API}

     * to allow applications to check such cross-loader references.

     * These checks apply to both the {@code MethodHandles.Lookup} API

     * and the Core Reflection API

     * (as found on {@link java.lang.Class Class}).

     * <p>

     * If a security manager is present, member and class lookups are subject to

     * additional checks.

     * From one to three calls are made to the security manager.

     * Any of these calls can refuse access by throwing a

     * {@link java.lang.SecurityException SecurityException}.

     * Define {@code smgr} as the security manager,

     * {@code lookc} as the lookup class of the current lookup object,

     * {@code refc} as the containing class in which the member

     * is being sought, and {@code defc} as the class in which the

     * member is actually defined.

     * (If a class or other type is being accessed,

     * the {@code refc} and {@code defc} values are the class itself.)

     * The value {@code lookc} is defined as <em>not present</em>

     * if the current lookup object does not have

     * <a href="MethodHandles.Lookup.html#privacc">private access</a>.

     * The calls are made according to the following rules:

     * <ul>

     * <li><b>Step 1:</b>

     *     If {@code lookc} is not present, or if its class loader is not

     *     the same as or an ancestor of the class loader of {@code refc},

     *     then {@link SecurityManager#checkPackageAccess

     *     smgr.checkPackageAccess(refcPkg)} is called,

     *     where {@code refcPkg} is the package of {@code refc}.

     * <li><b>Step 2a:</b>

     *     If the retrieved member is not public and

     *     {@code lookc} is not present, then

     *     {@link SecurityManager#checkPermission smgr.checkPermission}

     *     with {@code RuntimePermission("accessDeclaredMembers")} is called.

     * <li><b>Step 2b:</b>

     *     If the retrieved class has a {@code null} class loader,

     *     and {@code lookc} is not present, then

     *     {@link SecurityManager#checkPermission smgr.checkPermission}

     *     with {@code RuntimePermission("getClassLoader")} is called.

     * <li><b>Step 3:</b>

     *     If the retrieved member is not public,

     *     and if {@code lookc} is not present,

     *     and if {@code defc} and {@code refc} are different,

     *     then {@link SecurityManager#checkPackageAccess

     *     smgr.checkPackageAccess(defcPkg)} is called,

     *     where {@code defcPkg} is the package of {@code defc}.

     * </ul>

     * Security checks are performed after other access checks have passed.

     * Therefore, the above rules presuppose a member or class that is public,

     * or else that is being accessed from a lookup class that has

     * rights to access the member or class.

     *

     * <h1><a id="callsens"></a>Caller sensitive methods</h1>

     * A small number of Java methods have a special property called caller sensitivity.

     * A <em>caller-sensitive</em> method can behave differently depending on the

     * identity of its immediate caller.

     * <p>

     * If a method handle for a caller-sensitive method is requested,

     * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,

     * but they take account of the lookup class in a special way.

     * The resulting method handle behaves as if it were called

     * from an instruction contained in the lookup class,

     * so that the caller-sensitive method detects the lookup class.

     * (By contrast, the invoker of the method handle is disregarded.)

     * Thus, in the case of caller-sensitive methods,

     * different lookup classes may give rise to

     * differently behaving method handles.

     * <p>

     * In cases where the lookup object is

     * {@link MethodHandles#publicLookup() publicLookup()},

     * or some other lookup object without

     * <a href="MethodHandles.Lookup.html#privacc">private access</a>,

     * the lookup class is disregarded.

     * In such cases, no caller-sensitive method handle can be created,

     * access is forbidden, and the lookup fails with an

     * {@code IllegalAccessException}.

     * <p style="font-size:smaller;">

     * <em>Discussion:</em>

     * For example, the caller-sensitive method

     * {@link java.lang.Class#forName(String) Class.forName(x)}

     * can return varying classes or throw varying exceptions,

     * depending on the class loader of the class that calls it.

     * A public lookup of {@code Class.forName} will fail, because

     * there is no reasonable way to determine its bytecode behavior.

     * <p style="font-size:smaller;">

     * If an application caches method handles for broad sharing,

     * it should use {@code publicLookup()} to create them.

     * If there is a lookup of {@code Class.forName}, it will fail,

     * and the application must take appropriate action in that case.

     * It may be that a later lookup, perhaps during the invocation of a

     * bootstrap method, can incorporate the specific identity

     * of the caller, making the method accessible.

     * <p style="font-size:smaller;">

     * The function {@code MethodHandles.lookup} is caller sensitive

     * so that there can be a secure foundation for lookups.

     * Nearly all other methods in the JSR 292 API rely on lookup

     * objects to check access requests.

     *

     * @revised 9

     */

    public static final

    class Lookup {

        /** The class on behalf of whom the lookup is being performed. */

        private final Class<?> lookupClass;

        /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */

        private final int allowedModes;

        /** A single-bit mask representing {@code public} access,

         *  which may contribute to the result of {@link #lookupModes lookupModes}.

         *  The value, {@code 0x01}, happens to be the same as the value of the

         *  {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.

         */

        public static final int PUBLIC = Modifier.PUBLIC;

        /** A single-bit mask representing {@code private} access,

         *  which may contribute to the result of {@link #lookupModes lookupModes}.

         *  The value, {@code 0x02}, happens to be the same as the value of the

         *  {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.

         */

        public static final int PRIVATE = Modifier.PRIVATE;

        /** A single-bit mask representing {@code protected} access,

         *  which may contribute to the result of {@link #lookupModes lookupModes}.

         *  The value, {@code 0x04}, happens to be the same as the value of the

         *  {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.

         */

        public static final int PROTECTED = Modifier.PROTECTED;

        /** A single-bit mask representing {@code package} access (default access),

         *  which may contribute to the result of {@link #lookupModes lookupModes}.

         *  The value is {@code 0x08}, which does not correspond meaningfully to

         *  any particular {@linkplain java.lang.reflect.Modifier modifier bit}.

         */

        public static final int PACKAGE = Modifier.STATIC;

        /** A single-bit mask representing {@code module} access (default access),

         *  which may contribute to the result of {@link #lookupModes lookupModes}.

         *  The value is {@code 0x10}, which does not correspond meaningfully to

         *  any particular {@linkplain java.lang.reflect.Modifier modifier bit}.

         *  In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}

         *  with this lookup mode can access all public types in the module of the

         *  lookup class and public types in packages exported by other modules

         *  to the module of the lookup class.

         *  @since 9

         *  @spec JPMS

         */

        public static final int MODULE = PACKAGE << 1;

        /** A single-bit mask representing {@code unconditional} access

         *  which may contribute to the result of {@link #lookupModes lookupModes}.

         *  The value is {@code 0x20}, which does not correspond meaningfully to

         *  any particular {@linkplain java.lang.reflect.Modifier modifier bit}.

         *  A {@code Lookup} with this lookup mode assumes {@linkplain

         *  java.lang.Module#canRead(java.lang.Module) readability}.

         *  In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}

         *  with this lookup mode can access all public members of public types

         *  of all modules where the type is in a package that is {@link

         *  java.lang.Module#isExported(String) exported unconditionally}.

         *  @since 9

         *  @spec JPMS

         *  @see #publicLookup()

         */

        public static final int UNCONDITIONAL = PACKAGE << 2;

        private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);

        private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);

        private static final int TRUSTED   = -1;

        private static int fixmods(int mods) {

            mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);

            return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);

        }

        /** Tells which class is performing the lookup.  It is this class against

         *  which checks are performed for visibility and access permissions.

         *  <p>

         *  The class implies a maximum level of access permission,

         *  but the permissions may be additionally limited by the bitmask

         *  {@link #lookupModes lookupModes}, which controls whether non-public members

         *  can be accessed.

         *  @return the lookup class, on behalf of which this lookup object finds members

         */

        public Class<?> lookupClass() {

            return lookupClass;

        }

        // This is just for calling out to MethodHandleImpl.

        private Class<?> lookupClassOrNull() {

            return (allowedModes == TRUSTED) ? null : lookupClass;

        }

        /** Tells which access-protection classes of members this lookup object can produce.

         *  The result is a bit-mask of the bits

         *  {@linkplain #PUBLIC PUBLIC (0x01)},

         *  {@linkplain #PRIVATE PRIVATE (0x02)},

         *  {@linkplain #PROTECTED PROTECTED (0x04)},

         *  {@linkplain #PACKAGE PACKAGE (0x08)},

         *  {@linkplain #MODULE MODULE (0x10)},

         *  and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.

         *  <p>

         *  A freshly-created lookup object

         *  on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has

         *  all possible bits set, except {@code UNCONDITIONAL}.

         *  A lookup object on a new lookup class

         *  {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}

         *  may have some mode bits set to zero.

         *  Mode bits can also be

         *  {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.

         *  Once cleared, mode bits cannot be restored from the downgraded lookup object.

         *  The purpose of this is to restrict access via the new lookup object,

         *  so that it can access only names which can be reached by the original

         *  lookup object, and also by the new lookup class.

         *  @return the lookup modes, which limit the kinds of access performed by this lookup object

         *  @see #in

         *  @see #dropLookupMode

         *

         *  @revised 9

         *  @spec JPMS

         */

        public int lookupModes() {

            return allowedModes & ALL_MODES;

        }

        /** Embody the current class (the lookupClass) as a lookup class

         * for method handle creation.

         * Must be called by from a method in this package,

         * which in turn is called by a method not in this package.

         */

        Lookup(Class<?> lookupClass) {

            this(lookupClass, FULL_POWER_MODES);

            // make sure we haven't accidentally picked up a privileged class:

            checkUnprivilegedlookupClass(lookupClass);

        }

        private Lookup(Class<?> lookupClass, int allowedModes) {

            this.lookupClass = lookupClass;

            this.allowedModes = allowedModes;

        }

        /**

         * Creates a lookup on the specified new lookup class.

         * The resulting object will report the specified

         * class as its own {@link #lookupClass() lookupClass}.

         * <p>

         * However, the resulting {@code Lookup} object is guaranteed

         * to have no more access capabilities than the original.

         * In particular, access capabilities can be lost as follows:<ul>

         * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and

         * the new lookup class is in a different module {@code M}, then no members, not

         * even public members in {@code M}'s exported packages, will be accessible.

         * The exception to this is when this lookup is {@link #publicLookup()

         * publicLookup}, in which case {@code PUBLIC} access is not lost.

         * <li>If the old lookup class is in an unnamed module, and the new lookup class

         * is a different module then {@link #MODULE MODULE} access is lost.

         * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost.

         * <li>If the new lookup class is in a different package

         * than the old one, protected and default (package) members will not be accessible.

         * <li>If the new lookup class is not within the same package member

         * as the old one, private members will not be accessible, and protected members

         * will not be accessible by virtue of inheritance.

         * (Protected members may continue to be accessible because of package sharing.)

         * <li>If the new lookup class is not accessible to the old lookup class,

         * then no members, not even public members, will be accessible.

         * (In all other cases, public members will continue to be accessible.)

         * </ul>

         * <p>

         * The resulting lookup's capabilities for loading classes

         * (used during {@link #findClass} invocations)

         * are determined by the lookup class' loader,

         * which may change due to this operation.

         *

         * @param requestedLookupClass the desired lookup class for the new lookup object

         * @return a lookup object which reports the desired lookup class, or the same object

         * if there is no change

         * @throws NullPointerException if the argument is null

         *

         * @revised 9

         * @spec JPMS

         */

        public Lookup in(Class<?> requestedLookupClass) {

            Objects.requireNonNull(requestedLookupClass);

            if (allowedModes == TRUSTED)  // IMPL_LOOKUP can make any lookup at all

                return new Lookup(requestedLookupClass, FULL_POWER_MODES);

            if (requestedLookupClass == this.lookupClass)

                return this;  // keep same capabilities

            int newModes = (allowedModes & FULL_POWER_MODES);

            if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {

                // Need to drop all access when teleporting from a named module to another

                // module. The exception is publicLookup where PUBLIC is not lost.

                if (this.lookupClass.getModule().isNamed()

                    && (this.allowedModes & UNCONDITIONAL) == 0)

                    newModes = 0;

                else

                    newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);

            }

            if ((newModes & PACKAGE) != 0

                && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {

                newModes &= ~(PACKAGE|PRIVATE|PROTECTED);

            }

            // Allow nestmate lookups to be created without special privilege:

            if ((newModes & PRIVATE) != 0

                && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {

                newModes &= ~(PRIVATE|PROTECTED);

            }

            if ((newModes & PUBLIC) != 0

                && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {

                // The requested class it not accessible from the lookup class.

                // No permissions.

                newModes = 0;

            }

            checkUnprivilegedlookupClass(requestedLookupClass);

            return new Lookup(requestedLookupClass, newModes);

        }

        /**

         * Creates a lookup on the same lookup class which this lookup object

         * finds members, but with a lookup mode that has lost the given lookup mode.

         * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE

         * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.

         * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always

         * dropped and so the resulting lookup mode will never have these access capabilities.

         * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}

         * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will

         * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}

         * is dropped then the resulting lookup has no access.

         * @param modeToDrop the lookup mode to drop

         * @return a lookup object which lacks the indicated mode, or the same object if there is no change

         * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},

         * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}

         * @see MethodHandles#privateLookupIn

         * @since 9

         */

        public Lookup dropLookupMode(int modeToDrop) {

            int oldModes = lookupModes();

            int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);

            switch (modeToDrop) {

                case PUBLIC: newModes &= ~(ALL_MODES); break;

                case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;

                case PACKAGE: newModes &= ~(PRIVATE); break;

                case PROTECTED:

                case PRIVATE:

                case UNCONDITIONAL: break;

                default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");

            }

            if (newModes == oldModes) return this;  // return self if no change

            return new Lookup(lookupClass(), newModes);

        }

        /**

         * Defines a class to the same class loader and in the same runtime package and

         * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's

         * {@linkplain #lookupClass() lookup class}.

         *

         * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include

         * {@link #PACKAGE PACKAGE} access as default (package) members will be

         * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate

         * that the lookup object was created by a caller in the runtime package (or derived

         * from a lookup originally created by suitably privileged code to a target class in

         * the runtime package). </p>

         *

         * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined

         * by the <em>The Java Virtual Machine Specification</em>) with a class name in the

         * same package as the lookup class. </p>

         *

         * <p> This method does not run the class initializer. The class initializer may

         * run at a later time, as detailed in section 12.4 of the <em>The Java Language

         * Specification</em>. </p>

         *

         * <p> If there is a security manager, its {@code checkPermission} method is first called

         * to check {@code RuntimePermission("defineClass")}. </p>

         *

         * @param bytes the class bytes

         * @return the {@code Class} object for the class

         * @throws IllegalArgumentException the bytes are for a class in a different package

         * to the lookup class

         * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access

         * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be

         * verified ({@code VerifyError}), is already defined, or another linkage error occurs

         * @throws SecurityException if denied by the security manager

         * @throws NullPointerException if {@code bytes} is {@code null}

         * @since 9

         * @spec JPMS

         * @see Lookup#privateLookupIn

         * @see Lookup#dropLookupMode

         * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)

         */

        public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {

            SecurityManager sm = System.getSecurityManager();

            if (sm != null)

                sm.checkPermission(new RuntimePermission("defineClass"));

            if ((lookupModes() & PACKAGE) == 0)

                throw new IllegalAccessException("Lookup does not have PACKAGE access");

            assert (lookupModes() & (MODULE|PUBLIC)) != 0;

            // parse class bytes to get class name (in internal form)

            bytes = bytes.clone();

            String name;

            try {

                ClassReader reader = new ClassReader(bytes);

                name = reader.getClassName();

            } catch (RuntimeException e) {

                // ASM exceptions are poorly specified

                ClassFormatError cfe = new ClassFormatError();

                cfe.initCause(e);

                throw cfe;

            }

            // get package and class name in binary form

            String cn, pn;

            int index = name.lastIndexOf('/');

            if (index == -1) {

                cn = name;

                pn = "";

            } else {

                cn = name.replace('/', '.');

                pn = cn.substring(0, index);

            }

            if (!pn.equals(lookupClass.getPackageName())) {

                throw new IllegalArgumentException("Class not in same package as lookup class");

            }

            // invoke the class loader's defineClass method

            ClassLoader loader = lookupClass.getClassLoader();

            ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;

            String source = "__Lookup_defineClass__";

            Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);

            assert clazz.getClassLoader() == lookupClass.getClassLoader()

                    && clazz.getPackageName().equals(lookupClass.getPackageName())

                    && protectionDomain(clazz) == lookupClassProtectionDomain();

            return clazz;

        }

        private ProtectionDomain lookupClassProtectionDomain() {

            ProtectionDomain pd = cachedProtectionDomain;

            if (pd == null) {

                cachedProtectionDomain = pd = protectionDomain(lookupClass);

            }

            return pd;

        }

        private ProtectionDomain protectionDomain(Class<?> clazz) {

            PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;

            return AccessController.doPrivileged(pa);

        }

        // cached protection domain

        private volatile ProtectionDomain cachedProtectionDomain;

        // Make sure outer class is initialized first.

        static { IMPL_NAMES.getClass(); }

        /** Package-private version of lookup which is trusted. */

        static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);

        /** Version of lookup which is trusted minimally.

         *  It can only be used to create method handles to publicly accessible

         *  members in packages that are exported unconditionally.

         */

        static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));

        private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {

            String name = lookupClass.getName();

            if (name.startsWith("java.lang.invoke."))

                throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);

        }

        /**

         * Displays the name of the class from which lookups are to be made.

         * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)

         * If there are restrictions on the access permitted to this lookup,

         * this is indicated by adding a suffix to the class name, consisting

         * of a slash and a keyword.  The keyword represents the strongest

         * allowed access, and is chosen as follows:

         * <ul>

         * <li>If no access is allowed, the suffix is "/noaccess".

         * <li>If only public access to types in exported packages is allowed, the suffix is "/public".

         * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".

         * <li>If only public and module access are allowed, the suffix is "/module".

         * <li>If only public, module and package access are allowed, the suffix is "/package".

         * <li>If only public, module, package, and private access are allowed, the suffix is "/private".

         * </ul>

         * If none of the above cases apply, it is the case that full

         * access (public, module, package, private, and protected) is allowed.

         * In this case, no suffix is added.

         * This is true only of an object obtained originally from

         * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.

         * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}

         * always have restricted access, and will display a suffix.

         * <p>

         * (It may seem strange that protected access should be

         * stronger than private access.  Viewed independently from

         * package access, protected access is the first to be lost,

         * because it requires a direct subclass relationship between

         * caller and callee.)

         * @see #in

         *

         * @revised 9

         * @spec JPMS

         */

        @Override

        public String toString() {

            String cname = lookupClass.getName();

            switch (allowedModes) {

            case 0:  // no privileges

                return cname + "/noaccess";

            case PUBLIC:

                return cname + "/public";

            case PUBLIC|UNCONDITIONAL:

                return cname  + "/publicLookup";

            case PUBLIC|MODULE:

                return cname + "/module";

            case PUBLIC|MODULE|PACKAGE:

                return cname + "/package";

            case FULL_POWER_MODES & ~PROTECTED:

                return cname + "/private";

            case FULL_POWER_MODES:

                return cname;

            case TRUSTED:

                return "/trusted";  // internal only; not exported

            default:  // Should not happen, but it's a bitfield...

                cname = cname + "/" + Integer.toHexString(allowedModes);

                assert(false) : cname;

                return cname;

            }

        }

        /**

         * Produces a method handle for a static method.

         * The type of the method handle will be that of the method.

         * (Since static methods do not take receivers, there is no

         * additional receiver argument inserted into the method handle type,

         * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)

         * The method and all its argument types must be accessible to the lookup object.

         * <p>

         * The returned method handle will have

         * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if

         * the method's variable arity modifier bit ({@code 0x0080}) is set.

         * <p>

         * If the returned method handle is invoked, the method's class will

         * be initialized, if it has not already been initialized.

         * <p><b>Example:</b>

         * <blockquote><pre>{@code

import static java.lang.invoke.MethodHandles.*;

import static java.lang.invoke.MethodType.*;

...

MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,

  "asList", methodType(List.class, Object[].class));

assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());

         * }</pre></blockquote>

         * @param refc the class from which the method is accessed

         * @param name the name of the method

         * @param type the type of the method

         * @return the desired method handle

         * @throws NoSuchMethodException if the method does not exist

         * @throws IllegalAccessException if access checking fails,

         *                                or if the method is not {@code static},

         *                                or if the method's variable arity modifier bit

         *                                is set and {@code asVarargsCollector} fails

         * @exception SecurityException if a security manager is present and it

         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>

         * @throws NullPointerException if any argument is null

         */

        public

        MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {

            MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);

            return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));

        }

        /**

         * Produces a method handle for a virtual method.

         * The type of the method handle will be that of the method,

         * with the receiver type (usually {@code refc}) prepended.

         * The method and all its argument types must be accessible to the lookup object.

         * <p>

         * When called, the handle will treat the first argument as a receiver

         * and, for non-private methods, dispatch on the receiver's type to determine which method

         * implementation to enter.

         * For private methods the named method in {@code refc} will be invoked on the receiver.

         * (The dispatching action is identical with that performed by an

         * {@code invokevirtual} or {@code invokeinterface} instruction.)

         * <p>

         * The first argument will be of type {@code refc} if the lookup

         * class has full privileges to access the member.  Otherwise

         * the member must be {@code protected} and the first argument

         * will be restricted in type to the lookup class.

         * <p>

         * The returned method handle will have

         * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if

         * the method's variable arity modifier bit ({@code 0x0080}) is set.

         * <p>

         * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}

         * instructions and method handles produced by {@code findVirtual},

         * if the class is {@code MethodHandle} and the name string is

         * {@code invokeExact} or {@code invoke}, the resulting

         * method handle is equivalent to one produced by

         * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or

         * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}

         * with the same {@code type} argument.

         * <p>

         * If the class is {@code VarHandle} and the name string corresponds to

         * the name of a signature-polymorphic access mode method, the resulting

         * method handle is equivalent to one produced by

         * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with

         * the access mode corresponding to the name string and with the same

         * {@code type} arguments.

         * <p>

         * <b>Example:</b>

         * <blockquote><pre>{@code

import static java.lang.invoke.MethodHandles.*;

import static java.lang.invoke.MethodType.*;

...

MethodHandle MH_concat = publicLookup().findVirtual(String.class,

  "concat", methodType(String.class, String.class));

MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,

  "hashCode", methodType(int.class));

MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,

  "hashCode", methodType(int.class));

assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));

assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));

assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));

// interface method:

MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,

  "subSequence", methodType(CharSequence.class, int.class, int.class));

assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());

// constructor "internal method" must be accessed differently:

MethodType MT_newString = methodType(void.class); //()V for new String()

try { assertEquals("impossible", lookup()

        .findVirtual(String.class, "<init>", MT_newString));

 } catch (NoSuchMethodException ex) { } // OK

MethodHandle MH_newString = publicLookup()

  .findConstructor(String.class, MT_newString);

assertEquals("", (String) MH_newString.invokeExact());

         * }</pre></blockquote>

         *

         * @param refc the class or interface from which the method is accessed

         * @param name the name of the method

         * @param type the type of the method, with the receiver argument omitted

         * @return the desired method handle

         * @throws NoSuchMethodException if the method does not exist

         * @throws IllegalAccessException if access checking fails,

         *                                or if the method is {@code static},

         *                                or if the method's variable arity modifier bit

         *                                is set and {@code asVarargsCollector} fails

         * @exception SecurityException if a security manager is present and it

         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>

         * @throws NullPointerException if any argument is null

         */

        public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {

            if (refc == MethodHandle.class) {

                MethodHandle mh = findVirtualForMH(name, type);

                if (mh != null)  return mh;

            } else if (refc == VarHandle.class) {