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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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 constituent symbolic parts.
37 * To crack a direct method handle, call {@link Lookup#revealDirect Lookup.revealDirect}.
38 * <h2><a id="directmh"></a>Direct Method Handles</h2>
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 {@jvms
47 * 4.4.8} and {@jvms 5.4.3}.)
48 * <li>By calling one of the <a href="MethodHandles.Lookup.html#lookups">Lookup Factory Methods</a>,
49 * such as {@link Lookup#findVirtual Lookup.findVirtual},
50 * to resolve a symbolic reference into a method handle.
51 * A symbolic reference consists of a class, name string, and type.
52 * <li>By calling the factory method {@link Lookup#unreflect Lookup.unreflect}
53 * or {@link Lookup#unreflectSpecial Lookup.unreflectSpecial}
54 * to convert a {@link Method} into a method handle.
55 * <li>By calling the factory method {@link Lookup#unreflectConstructor Lookup.unreflectConstructor}
56 * to convert a {@link Constructor} into a method handle.
57 * <li>By calling the factory method {@link Lookup#unreflectGetter Lookup.unreflectGetter}
58 * or {@link Lookup#unreflectSetter Lookup.unreflectSetter}
59 * to convert a {@link Field} into a method handle.
60 * </ul>
61 *
62 * <h2>Restrictions on Cracking</h2>
63 * Given a suitable {@code Lookup} object, it is possible to crack any direct method handle
64 * to recover a symbolic reference for the underlying method, constructor, or field.
65 * Cracking must be done via a {@code Lookup} object equivalent to that which created
66 * the target method handle, or which has enough access permissions to recreate
67 * an equivalent method handle.
68 * <p>
69 * If the underlying method is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>,
70 * the direct method handle will have been "bound" to a particular caller class, the
71 * {@linkplain java.lang.invoke.MethodHandles.Lookup#lookupClass() lookup class}
72 * of the lookup object used to create it.
73 * Cracking this method handle with a different lookup class will fail
74 * even if the underlying method is public (like {@code Class.forName}).
75 * <p>
76 * The requirement of lookup object matching provides a "fast fail" behavior
77 * for programs which may otherwise trust erroneous revelation of a method
78 * handle with symbolic information (or caller binding) from an unexpected scope.
79 * Use {@link java.lang.invoke.MethodHandles#reflectAs} to override this limitation.
80 *
81 * <h2><a id="refkinds"></a>Reference kinds</h2>
82 * The <a href="MethodHandles.Lookup.html#lookups">Lookup Factory Methods</a>
83 * correspond to all major use cases for methods, constructors, and fields.
84 * These use cases may be distinguished using small integers as follows:
85 * <table class="striped">
86 * <caption style="display:none">reference kinds</caption>
87 * <thead>
88 * <tr><th scope="col">reference kind</th><th scope="col">descriptive name</th><th scope="col">scope</th><th scope="col">member</th><th scope="col">behavior</th></tr>
89 * </thead>
90 * <tbody>
91 * <tr>
92 * <th scope="row">{@code 1}</th><td>{@code REF_getField}</td><td>{@code class}</td>
93 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
94 * </tr>
95 * <tr>
96 * <th scope="row">{@code 2}</th><td>{@code REF_getStatic}</td><td>{@code class} or {@code interface}</td>
97 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
98 * </tr>
99 * <tr>
100 * <th scope="row">{@code 3}</th><td>{@code REF_putField}</td><td>{@code class}</td>
101 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
102 * </tr>
103 * <tr>
104 * <th scope="row">{@code 4}</th><td>{@code REF_putStatic}</td><td>{@code class}</td>
105 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
106 * </tr>
107 * <tr>
108 * <th scope="row">{@code 5}</th><td>{@code REF_invokeVirtual}</td><td>{@code class}</td>
109 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
110 * </tr>
111 * <tr>
112 * <th scope="row">{@code 6}</th><td>{@code REF_invokeStatic}</td><td>{@code class} or {@code interface}</td>
113 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
114 * </tr>
115 * <tr>
116 * <th scope="row">{@code 7}</th><td>{@code REF_invokeSpecial}</td><td>{@code class} or {@code interface}</td>
117 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
118 * </tr>
119 * <tr>
120 * <th scope="row">{@code 8}</th><td>{@code REF_newInvokeSpecial}</td><td>{@code class}</td>
121 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
122 * </tr>
123 * <tr>
124 * <th scope="row">{@code 9}</th><td>{@code REF_invokeInterface}</td><td>{@code interface}</td>
125 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
126 * </tr>
127 * </tbody>
128 * </table>
129 * @since 1.8
130 */
131 public 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 * @throws ClassCastException if the member is not of the expected type
203 * @throws NullPointerException if either argument is {@code null}
204 * @throws 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 * @throws 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 * @throws IllegalArgumentException if the first argument is not a valid
282 * <a href="MethodHandleInfo.html#refkinds">reference kind number</a>
283 * @throws 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 }