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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
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  25 
  26 package java.lang.invoke;
  27 
  28 import java.lang.reflect.*;
  29 import java.util.*;
  30 import java.lang.invoke.MethodHandleNatives.Constants;
  31 import java.lang.invoke.MethodHandles.Lookup;
  32 import static java.lang.invoke.MethodHandleStatics.*;
  33 
  34 /**
  35  * A symbolic reference obtained by cracking a direct method handle
  36  * into its consitutent symbolic parts.
  37  * To crack a direct method handle, call {@link Lookup#revealDirect Lookup.revealDirect}.
  38  * <h1><a id="directmh"></a>Direct Method Handles</h1>
  39  * A <em>direct method handle</em> represents a method, constructor, or field without
  40  * any intervening argument bindings or other transformations.
  41  * The method, constructor, or field referred to by a direct method handle is called
  42  * its <em>underlying member</em>.
  43  * Direct method handles may be obtained in any of these ways:
  44  * <ul>
  45  * <li>By executing an {@code ldc} instruction on a {@code CONSTANT_MethodHandle} constant.
  46  *     (See the Java Virtual Machine Specification, sections 4.4.8 and 5.4.3.)
  47  * <li>By calling one of the <a href="MethodHandles.Lookup.html#lookups">Lookup Factory Methods</a>,
  48  *     such as {@link Lookup#findVirtual Lookup.findVirtual},
  49  *     to resolve a symbolic reference into a method handle.
  50  *     A symbolic reference consists of a class, name string, and type.
  51  * <li>By calling the factory method {@link Lookup#unreflect Lookup.unreflect}
  52  *     or {@link Lookup#unreflectSpecial Lookup.unreflectSpecial}
  53  *     to convert a {@link Method} into a method handle.
  54  * <li>By calling the factory method {@link Lookup#unreflectConstructor Lookup.unreflectConstructor}
  55  *     to convert a {@link Constructor} into a method handle.
  56  * <li>By calling the factory method {@link Lookup#unreflectGetter Lookup.unreflectGetter}
  57  *     or {@link Lookup#unreflectSetter Lookup.unreflectSetter}
  58  *     to convert a {@link Field} into a method handle.
  59  * </ul>
  60  *
  61  * <h1>Restrictions on Cracking</h1>
  62  * Given a suitable {@code Lookup} object, it is possible to crack any direct method handle
  63  * to recover a symbolic reference for the underlying method, constructor, or field.
  64  * Cracking must be done via a {@code Lookup} object equivalent to that which created
  65  * the target method handle, or which has enough access permissions to recreate
  66  * an equivalent method handle.
  67  * <p>
  68  * If the underlying method is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>,
  69  * the direct method handle will have been "bound" to a particular caller class, the
  70  * {@linkplain java.lang.invoke.MethodHandles.Lookup#lookupClass() lookup class}
  71  * of the lookup object used to create it.
  72  * Cracking this method handle with a different lookup class will fail
  73  * even if the underlying method is public (like {@code Class.forName}).
  74  * <p>
  75  * The requirement of lookup object matching provides a "fast fail" behavior
  76  * for programs which may otherwise trust erroneous revelation of a method
  77  * handle with symbolic information (or caller binding) from an unexpected scope.
  78  * Use {@link java.lang.invoke.MethodHandles#reflectAs} to override this limitation.
  79  *
  80  * <h1><a id="refkinds"></a>Reference kinds</h1>
  81  * The <a href="MethodHandles.Lookup.html#lookups">Lookup Factory Methods</a>
  82  * correspond to all major use cases for methods, constructors, and fields.
  83  * These use cases may be distinguished using small integers as follows:
  84  * <table class="striped">
  85  * <caption style="display:none">reference kinds</caption>
  86  * <thead>
  87  * <tr><th>reference kind</th><th>descriptive name</th><th>scope</th><th>member</th><th>behavior</th></tr>
  88  * </thead>
  89  * <tbody>
  90  * <tr>
  91  *     <td>{@code 1}</td><td>{@code REF_getField}</td><td>{@code class}</td>
  92  *     <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
  93  * </tr>
  94  * <tr>
  95  *     <td>{@code 2}</td><td>{@code REF_getStatic}</td><td>{@code class} or {@code interface}</td>
  96  *     <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
  97  * </tr>
  98  * <tr>
  99  *     <td>{@code 3}</td><td>{@code REF_putField}</td><td>{@code class}</td>
 100  *     <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
 101  * </tr>
 102  * <tr>
 103  *     <td>{@code 4}</td><td>{@code REF_putStatic}</td><td>{@code class}</td>
 104  *     <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
 105  * </tr>
 106  * <tr>
 107  *     <td>{@code 5}</td><td>{@code REF_invokeVirtual}</td><td>{@code class}</td>
 108  *     <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
 109  * </tr>
 110  * <tr>
 111  *     <td>{@code 6}</td><td>{@code REF_invokeStatic}</td><td>{@code class} or {@code interface}</td>
 112  *     <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
 113  * </tr>
 114  * <tr>
 115  *     <td>{@code 7}</td><td>{@code REF_invokeSpecial}</td><td>{@code class} or {@code interface}</td>
 116  *     <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
 117  * </tr>
 118  * <tr>
 119  *     <td>{@code 8}</td><td>{@code REF_newInvokeSpecial}</td><td>{@code class}</td>
 120  *     <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
 121  * </tr>
 122  * <tr>
 123  *     <td>{@code 9}</td><td>{@code REF_invokeInterface}</td><td>{@code interface}</td>
 124  *     <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
 125  * </tr>
 126  * </tbody>
 127  * </table>
 128  * @since 1.8
 129  */
 130 public
 131 interface MethodHandleInfo {
 132     /**
 133      * A direct method handle reference kind,
 134      * as defined in the <a href="MethodHandleInfo.html#refkinds">table above</a>.
 135      */
 136     public static final int
 137         REF_getField                = Constants.REF_getField,
 138         REF_getStatic               = Constants.REF_getStatic,
 139         REF_putField                = Constants.REF_putField,
 140         REF_putStatic               = Constants.REF_putStatic,
 141         REF_invokeVirtual           = Constants.REF_invokeVirtual,
 142         REF_invokeStatic            = Constants.REF_invokeStatic,
 143         REF_invokeSpecial           = Constants.REF_invokeSpecial,
 144         REF_newInvokeSpecial        = Constants.REF_newInvokeSpecial,
 145         REF_invokeInterface         = Constants.REF_invokeInterface;
 146 
 147     /**
 148      * Returns the reference kind of the cracked method handle, which in turn
 149      * determines whether the method handle's underlying member was a constructor, method, or field.
 150      * See the <a href="MethodHandleInfo.html#refkinds">table above</a> for definitions.
 151      * @return the integer code for the kind of reference used to access the underlying member
 152      */
 153     public int getReferenceKind();
 154 
 155     /**
 156      * Returns the class in which the cracked method handle's underlying member was defined.
 157      * @return the declaring class of the underlying member
 158      */
 159     public Class<?> getDeclaringClass();
 160 
 161     /**
 162      * Returns the name of the cracked method handle's underlying member.
 163      * This is {@code "<init>"} if the underlying member was a constructor,
 164      * else it is a simple method name or field name.
 165      * @return the simple name of the underlying member
 166      */
 167     public String getName();
 168 
 169     /**
 170      * Returns the nominal type of the cracked symbolic reference, expressed as a method type.
 171      * If the reference is to a constructor, the return type will be {@code void}.
 172      * If it is to a non-static method, the method type will not mention the {@code this} parameter.
 173      * If it is to a field and the requested access is to read the field,
 174      * the method type will have no parameters and return the field type.
 175      * If it is to a field and the requested access is to write the field,
 176      * the method type will have one parameter of the field type and return {@code void}.
 177      * <p>
 178      * Note that original direct method handle may include a leading {@code this} parameter,
 179      * or (in the case of a constructor) will replace the {@code void} return type
 180      * with the constructed class.
 181      * The nominal type does not include any {@code this} parameter,
 182      * and (in the case of a constructor) will return {@code void}.
 183      * @return the type of the underlying member, expressed as a method type
 184      */
 185     public MethodType getMethodType();
 186 
 187     // Utility methods.
 188     // NOTE: class/name/type and reference kind constitute a symbolic reference
 189     // member and modifiers are an add-on, derived from Core Reflection (or the equivalent)
 190 
 191     /**
 192      * Reflects the underlying member as a method, constructor, or field object.
 193      * If the underlying member is public, it is reflected as if by
 194      * {@code getMethod}, {@code getConstructor}, or {@code getField}.
 195      * Otherwise, it is reflected as if by
 196      * {@code getDeclaredMethod}, {@code getDeclaredConstructor}, or {@code getDeclaredField}.
 197      * The underlying member must be accessible to the given lookup object.
 198      * @param <T> the desired type of the result, either {@link Member} or a subtype
 199      * @param expected a class object representing the desired result type {@code T}
 200      * @param lookup the lookup object that created this MethodHandleInfo, or one with equivalent access privileges
 201      * @return a reference to the method, constructor, or field object
 202      * @exception ClassCastException if the member is not of the expected type
 203      * @exception NullPointerException if either argument is {@code null}
 204      * @exception IllegalArgumentException if the underlying member is not accessible to the given lookup object
 205      */
 206     public <T extends Member> T reflectAs(Class<T> expected, Lookup lookup);
 207 
 208     /**
 209      * Returns the access modifiers of the underlying member.
 210      * @return the Java language modifiers for underlying member,
 211      *         or -1 if the member cannot be accessed
 212      * @see Modifier
 213      * @see #reflectAs
 214      */
 215     public int getModifiers();
 216 
 217     /**
 218      * Determines if the underlying member was a variable arity method or constructor.
 219      * Such members are represented by method handles that are varargs collectors.
 220      * @implSpec
 221      * This produces a result equivalent to:
 222      * <pre>{@code
 223      *     getReferenceKind() >= REF_invokeVirtual && Modifier.isTransient(getModifiers())
 224      * }</pre>
 225      *
 226      *
 227      * @return {@code true} if and only if the underlying member was declared with variable arity.
 228      */
 229     // spelling derived from java.lang.reflect.Executable, not MethodHandle.isVarargsCollector
 230     public default boolean isVarArgs()  {
 231         // fields are never varargs:
 232         if (MethodHandleNatives.refKindIsField((byte) getReferenceKind()))
 233             return false;
 234         // not in the public API: Modifier.VARARGS
 235         final int ACC_VARARGS = 0x00000080;  // from JVMS 4.6 (Table 4.20)
 236         assert(ACC_VARARGS == Modifier.TRANSIENT);
 237         return Modifier.isTransient(getModifiers());
 238     }
 239 
 240     /**
 241      * Returns the descriptive name of the given reference kind,
 242      * as defined in the <a href="MethodHandleInfo.html#refkinds">table above</a>.
 243      * The conventional prefix "REF_" is omitted.
 244      * @param referenceKind an integer code for a kind of reference used to access a class member
 245      * @return a mixed-case string such as {@code "getField"}
 246      * @exception IllegalArgumentException if the argument is not a valid
 247      *            <a href="MethodHandleInfo.html#refkinds">reference kind number</a>
 248      */
 249     public static String referenceKindToString(int referenceKind) {
 250         if (!MethodHandleNatives.refKindIsValid(referenceKind))
 251             throw newIllegalArgumentException("invalid reference kind", referenceKind);
 252         return MethodHandleNatives.refKindName((byte)referenceKind);
 253     }
 254 
 255     /**
 256      * Returns a string representation for a {@code MethodHandleInfo},
 257      * given the four parts of its symbolic reference.
 258      * This is defined to be of the form {@code "RK C.N:MT"}, where {@code RK} is the
 259      * {@linkplain #referenceKindToString reference kind string} for {@code kind},
 260      * {@code C} is the {@linkplain java.lang.Class#getName name} of {@code defc}
 261      * {@code N} is the {@code name}, and
 262      * {@code MT} is the {@code type}.
 263      * These four values may be obtained from the
 264      * {@linkplain #getReferenceKind reference kind},
 265      * {@linkplain #getDeclaringClass declaring class},
 266      * {@linkplain #getName member name},
 267      * and {@linkplain #getMethodType method type}
 268      * of a {@code MethodHandleInfo} object.
 269      *
 270      * @implSpec
 271      * This produces a result equivalent to:
 272      * <pre>{@code
 273      *     String.format("%s %s.%s:%s", referenceKindToString(kind), defc.getName(), name, type)
 274      * }</pre>
 275      *
 276      * @param kind the {@linkplain #getReferenceKind reference kind} part of the symbolic reference
 277      * @param defc the {@linkplain #getDeclaringClass declaring class} part of the symbolic reference
 278      * @param name the {@linkplain #getName member name} part of the symbolic reference
 279      * @param type the {@linkplain #getMethodType method type} part of the symbolic reference
 280      * @return a string of the form {@code "RK C.N:MT"}
 281      * @exception IllegalArgumentException if the first argument is not a valid
 282      *            <a href="MethodHandleInfo.html#refkinds">reference kind number</a>
 283      * @exception NullPointerException if any reference argument is {@code null}
 284      */
 285     public static String toString(int kind, Class<?> defc, String name, MethodType type) {
 286         Objects.requireNonNull(name); Objects.requireNonNull(type);
 287         return String.format("%s %s.%s:%s", referenceKindToString(kind), defc.getName(), name, type);
 288     }
 289 }