1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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14 * version 2 for more details (a copy is included in the LICENSE file that
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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 * <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 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 * <h2>Restrictions on Cracking</h2>
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 * <h2><a id="refkinds"></a>Reference kinds</h2>
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 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>
88 * </thead>
89 * <tbody>
90 * <tr>
91 * <th scope="row">{@code 1}</th><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 * <th scope="row">{@code 2}</th><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 * <th scope="row">{@code 3}</th><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 * <th scope="row">{@code 4}</th><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 * <th scope="row">{@code 5}</th><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 * <th scope="row">{@code 6}</th><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 * <th scope="row">{@code 7}</th><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 * <th scope="row">{@code 8}</th><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 * <th scope="row">{@code 9}</th><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 interface MethodHandleInfo {
131 /**
132 * A direct method handle reference kind,
133 * as defined in the <a href="MethodHandleInfo.html#refkinds">table above</a>.
134 */
135 public static final int
136 REF_getField = Constants.REF_getField,
137 REF_getStatic = Constants.REF_getStatic,
138 REF_putField = Constants.REF_putField,
139 REF_putStatic = Constants.REF_putStatic,
140 REF_invokeVirtual = Constants.REF_invokeVirtual,
141 REF_invokeStatic = Constants.REF_invokeStatic,
142 REF_invokeSpecial = Constants.REF_invokeSpecial,
143 REF_newInvokeSpecial = Constants.REF_newInvokeSpecial,
144 REF_invokeInterface = Constants.REF_invokeInterface;
145
146 /**
147 * Returns the reference kind of the cracked method handle, which in turn
148 * determines whether the method handle's underlying member was a constructor, method, or field.
149 * See the <a href="MethodHandleInfo.html#refkinds">table above</a> for definitions.
150 * @return the integer code for the kind of reference used to access the underlying member
151 */
152 public int getReferenceKind();
153
154 /**
155 * Returns the class in which the cracked method handle's underlying member was defined.
156 * @return the declaring class of the underlying member
157 */
158 public Class<?> getDeclaringClass();
159
160 /**
161 * Returns the name of the cracked method handle's underlying member.
162 * This is {@code "<init>"} if the underlying member was a constructor,
163 * else it is a simple method name or field name.
164 * @return the simple name of the underlying member
165 */
166 public String getName();
167
168 /**
169 * Returns the nominal type of the cracked symbolic reference, expressed as a method type.
170 * If the reference is to a constructor, the return type will be {@code void}.
171 * If it is to a non-static method, the method type will not mention the {@code this} parameter.
172 * If it is to a field and the requested access is to read the field,
173 * the method type will have no parameters and return the field type.
174 * If it is to a field and the requested access is to write the field,
175 * the method type will have one parameter of the field type and return {@code void}.
176 * <p>
177 * Note that original direct method handle may include a leading {@code this} parameter,
178 * or (in the case of a constructor) will replace the {@code void} return type
179 * with the constructed class.
180 * The nominal type does not include any {@code this} parameter,
181 * and (in the case of a constructor) will return {@code void}.
182 * @return the type of the underlying member, expressed as a method type
183 */
184 public MethodType getMethodType();
185
186 // Utility methods.
187 // NOTE: class/name/type and reference kind constitute a symbolic reference
188 // member and modifiers are an add-on, derived from Core Reflection (or the equivalent)
189
190 /**
191 * Reflects the underlying member as a method, constructor, or field object.
192 * If the underlying member is public, it is reflected as if by
193 * {@code getMethod}, {@code getConstructor}, or {@code getField}.
194 * Otherwise, it is reflected as if by
195 * {@code getDeclaredMethod}, {@code getDeclaredConstructor}, or {@code getDeclaredField}.
196 * The underlying member must be accessible to the given lookup object.
197 * @param <T> the desired type of the result, either {@link Member} or a subtype
198 * @param expected a class object representing the desired result type {@code T}
199 * @param lookup the lookup object that created this MethodHandleInfo, or one with equivalent access privileges
200 * @return a reference to the method, constructor, or field object
201 * @throws ClassCastException if the member is not of the expected type
202 * @throws NullPointerException if either argument is {@code null}
203 * @throws IllegalArgumentException if the underlying member is not accessible to the given lookup object
204 */
205 public <T extends Member> T reflectAs(Class<T> expected, Lookup lookup);
206
207 /**
208 * Returns the access modifiers of the underlying member.
209 * @return the Java language modifiers for underlying member,
210 * or -1 if the member cannot be accessed
211 * @see Modifier
212 * @see #reflectAs
213 */
214 public int getModifiers();
215
216 /**
217 * Determines if the underlying member was a variable arity method or constructor.
218 * Such members are represented by method handles that are varargs collectors.
219 * @implSpec
220 * This produces a result equivalent to:
221 * <pre>{@code
222 * getReferenceKind() >= REF_invokeVirtual && Modifier.isTransient(getModifiers())
223 * }</pre>
224 *
225 *
226 * @return {@code true} if and only if the underlying member was declared with variable arity.
227 */
228 // spelling derived from java.lang.reflect.Executable, not MethodHandle.isVarargsCollector
229 public default boolean isVarArgs() {
230 // fields are never varargs:
231 if (MethodHandleNatives.refKindIsField((byte) getReferenceKind()))
232 return false;
233 // not in the public API: Modifier.VARARGS
234 final int ACC_VARARGS = 0x00000080; // from JVMS 4.6 (Table 4.20)
235 assert(ACC_VARARGS == Modifier.TRANSIENT);
236 return Modifier.isTransient(getModifiers());
237 }
238
239 /**
240 * Returns the descriptive name of the given reference kind,
241 * as defined in the <a href="MethodHandleInfo.html#refkinds">table above</a>.
242 * The conventional prefix "REF_" is omitted.
243 * @param referenceKind an integer code for a kind of reference used to access a class member
244 * @return a mixed-case string such as {@code "getField"}
245 * @throws IllegalArgumentException if the argument is not a valid
246 * <a href="MethodHandleInfo.html#refkinds">reference kind number</a>
247 */
248 public static String referenceKindToString(int referenceKind) {
249 if (!MethodHandleNatives.refKindIsValid(referenceKind))
250 throw newIllegalArgumentException("invalid reference kind", referenceKind);
251 return MethodHandleNatives.refKindName((byte)referenceKind);
252 }
253
254 /**
255 * Returns a string representation for a {@code MethodHandleInfo},
256 * given the four parts of its symbolic reference.
257 * This is defined to be of the form {@code "RK C.N:MT"}, where {@code RK} is the
258 * {@linkplain #referenceKindToString reference kind string} for {@code kind},
259 * {@code C} is the {@linkplain java.lang.Class#getName name} of {@code defc}
260 * {@code N} is the {@code name}, and
261 * {@code MT} is the {@code type}.
262 * These four values may be obtained from the
263 * {@linkplain #getReferenceKind reference kind},
264 * {@linkplain #getDeclaringClass declaring class},
265 * {@linkplain #getName member name},
266 * and {@linkplain #getMethodType method type}
267 * of a {@code MethodHandleInfo} object.
268 *
269 * @implSpec
270 * This produces a result equivalent to:
271 * <pre>{@code
272 * String.format("%s %s.%s:%s", referenceKindToString(kind), defc.getName(), name, type)
273 * }</pre>
274 *
275 * @param kind the {@linkplain #getReferenceKind reference kind} part of the symbolic reference
276 * @param defc the {@linkplain #getDeclaringClass declaring class} part of the symbolic reference
277 * @param name the {@linkplain #getName member name} part of the symbolic reference
278 * @param type the {@linkplain #getMethodType method type} part of the symbolic reference
279 * @return a string of the form {@code "RK C.N:MT"}
280 * @throws IllegalArgumentException if the first argument is not a valid
281 * <a href="MethodHandleInfo.html#refkinds">reference kind number</a>
282 * @throws NullPointerException if any reference argument is {@code null}
283 */
284 public static String toString(int kind, Class<?> defc, String name, MethodType type) {
285 Objects.requireNonNull(name); Objects.requireNonNull(type);
286 return String.format("%s %s.%s:%s", referenceKindToString(kind), defc.getName(), name, type);
287 }
288 }