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package java.lang.invoke;
import java.lang.reflect.*;
import java.util.*;
import java.lang.invoke.MethodHandleNatives.Constants;
import java.lang.invoke.MethodHandles.Lookup;
import static java.lang.invoke.MethodHandleStatics.*;
/**
* A symbolic reference obtained by cracking a direct method handle
* into its constituent symbolic parts.
* To crack a direct method handle, call {@link Lookup#revealDirect Lookup.revealDirect}.
* Direct Method Handles
* A direct method handle represents a method, constructor, or field without
* any intervening argument bindings or other transformations.
* The method, constructor, or field referred to by a direct method handle is called
* its underlying member.
* Direct method handles may be obtained in any of these ways:
*
* - By executing an {@code ldc} instruction on a {@code CONSTANT_MethodHandle} constant.
* (See the Java Virtual Machine Specification, sections {@jvms
* 4.4.8} and {@jvms 5.4.3}.)
*
- By calling one of the Lookup Factory Methods,
* such as {@link Lookup#findVirtual Lookup.findVirtual},
* to resolve a symbolic reference into a method handle.
* A symbolic reference consists of a class, name string, and type.
*
- By calling the factory method {@link Lookup#unreflect Lookup.unreflect}
* or {@link Lookup#unreflectSpecial Lookup.unreflectSpecial}
* to convert a {@link Method} into a method handle.
*
- By calling the factory method {@link Lookup#unreflectConstructor Lookup.unreflectConstructor}
* to convert a {@link Constructor} into a method handle.
*
- By calling the factory method {@link Lookup#unreflectGetter Lookup.unreflectGetter}
* or {@link Lookup#unreflectSetter Lookup.unreflectSetter}
* to convert a {@link Field} into a method handle.
*
*
* Restrictions on Cracking
* Given a suitable {@code Lookup} object, it is possible to crack any direct method handle
* to recover a symbolic reference for the underlying method, constructor, or field.
* Cracking must be done via a {@code Lookup} object equivalent to that which created
* the target method handle, or which has enough access permissions to recreate
* an equivalent method handle.
*
* If the underlying method is caller sensitive,
* the direct method handle will have been "bound" to a particular caller class, the
* {@linkplain java.lang.invoke.MethodHandles.Lookup#lookupClass() lookup class}
* of the lookup object used to create it.
* Cracking this method handle with a different lookup class will fail
* even if the underlying method is public (like {@code Class.forName}).
*
* The requirement of lookup object matching provides a "fast fail" behavior
* for programs which may otherwise trust erroneous revelation of a method
* handle with symbolic information (or caller binding) from an unexpected scope.
* Use {@link java.lang.invoke.MethodHandles#reflectAs} to override this limitation.
*
*
Reference kinds
* The Lookup Factory Methods
* correspond to all major use cases for methods, constructors, and fields.
* These use cases may be distinguished using small integers as follows:
*
*
*
* reference kind descriptive name scope member behavior
* {@code 1} {@code REF_getField} {@code class}
* {@code FT f;} {@code (T) this.f;}
*
*
* {@code 2} {@code REF_getStatic} {@code class} or {@code interface}
* {@code static}
{@code FT f;} {@code (T) C.f;}
*
*
* {@code 3} {@code REF_putField} {@code class}
* {@code FT f;} {@code this.f = x;}
*
*
* {@code 4} {@code REF_putStatic} {@code class}
* {@code static}
{@code FT f;} {@code C.f = arg;}
*
*
* {@code 5} {@code REF_invokeVirtual} {@code class}
* {@code T m(A*);} {@code (T) this.m(arg*);}
*
*
* {@code 6} {@code REF_invokeStatic} {@code class} or {@code interface}
* {@code static}
{@code T m(A*);} {@code (T) C.m(arg*);}
*
*
* {@code 7} {@code REF_invokeSpecial} {@code class} or {@code interface}
* {@code T m(A*);} {@code (T) super.m(arg*);}
*
*
* {@code 8} {@code REF_newInvokeSpecial} {@code class}
* {@code C(A*);} {@code new C(arg*);}
*
*
* {@code 9} {@code REF_invokeInterface} {@code interface}
* {@code T m(A*);} {@code (T) this.m(arg*);}
*
*
*
* @since 1.8
*/
public interface MethodHandleInfo {
/**
* A direct method handle reference kind,
* as defined in the table above.
*/
public static final int
REF_getField = Constants.REF_getField,
REF_getStatic = Constants.REF_getStatic,
REF_putField = Constants.REF_putField,
REF_putStatic = Constants.REF_putStatic,
REF_invokeVirtual = Constants.REF_invokeVirtual,
REF_invokeStatic = Constants.REF_invokeStatic,
REF_invokeSpecial = Constants.REF_invokeSpecial,
REF_newInvokeSpecial = Constants.REF_newInvokeSpecial,
REF_invokeInterface = Constants.REF_invokeInterface;
/**
* Returns the reference kind of the cracked method handle, which in turn
* determines whether the method handle's underlying member was a constructor, method, or field.
* See the table above for definitions.
* @return the integer code for the kind of reference used to access the underlying member
*/
public int getReferenceKind();
/**
* Returns the class in which the cracked method handle's underlying member was defined.
* @return the declaring class of the underlying member
*/
public Class getDeclaringClass();
/**
* Returns the name of the cracked method handle's underlying member.
* This is {@code ""} if the underlying member was a constructor,
* else it is a simple method name or field name.
* @return the simple name of the underlying member
*/
public String getName();
/**
* Returns the nominal type of the cracked symbolic reference, expressed as a method type.
* If the reference is to a constructor, the return type will be {@code void}.
* If it is to a non-static method, the method type will not mention the {@code this} parameter.
* If it is to a field and the requested access is to read the field,
* the method type will have no parameters and return the field type.
* If it is to a field and the requested access is to write the field,
* the method type will have one parameter of the field type and return {@code void}.
*
* Note that original direct method handle may include a leading {@code this} parameter,
* or (in the case of a constructor) will replace the {@code void} return type
* with the constructed class.
* The nominal type does not include any {@code this} parameter,
* and (in the case of a constructor) will return {@code void}.
* @return the type of the underlying member, expressed as a method type
*/
public MethodType getMethodType();
// Utility methods.
// NOTE: class/name/type and reference kind constitute a symbolic reference
// member and modifiers are an add-on, derived from Core Reflection (or the equivalent)
/**
* Reflects the underlying member as a method, constructor, or field object.
* If the underlying member is public, it is reflected as if by
* {@code getMethod}, {@code getConstructor}, or {@code getField}.
* Otherwise, it is reflected as if by
* {@code getDeclaredMethod}, {@code getDeclaredConstructor}, or {@code getDeclaredField}.
* The underlying member must be accessible to the given lookup object.
* @param the desired type of the result, either {@link Member} or a subtype
* @param expected a class object representing the desired result type {@code T}
* @param lookup the lookup object that created this MethodHandleInfo, or one with equivalent access privileges
* @return a reference to the method, constructor, or field object
* @throws ClassCastException if the member is not of the expected type
* @throws NullPointerException if either argument is {@code null}
* @throws IllegalArgumentException if the underlying member is not accessible to the given lookup object
*/
public T reflectAs(Class expected, Lookup lookup);
/**
* Returns the access modifiers of the underlying member.
* @return the Java language modifiers for underlying member,
* or -1 if the member cannot be accessed
* @see Modifier
* @see #reflectAs
*/
public int getModifiers();
/**
* Determines if the underlying member was a variable arity method or constructor.
* Such members are represented by method handles that are varargs collectors.
* @implSpec
* This produces a result equivalent to:
* {@code
* getReferenceKind() >= REF_invokeVirtual && Modifier.isTransient(getModifiers())
* }
*
*
* @return {@code true} if and only if the underlying member was declared with variable arity.
*/
// spelling derived from java.lang.reflect.Executable, not MethodHandle.isVarargsCollector
public default boolean isVarArgs() {
// fields are never varargs:
if (MethodHandleNatives.refKindIsField((byte) getReferenceKind()))
return false;
// not in the public API: Modifier.VARARGS
final int ACC_VARARGS = 0x00000080; // from JVMS 4.6 (Table 4.20)
assert(ACC_VARARGS == Modifier.TRANSIENT);
return Modifier.isTransient(getModifiers());
}
/**
* Returns the descriptive name of the given reference kind,
* as defined in the table above.
* The conventional prefix "REF_" is omitted.
* @param referenceKind an integer code for a kind of reference used to access a class member
* @return a mixed-case string such as {@code "getField"}
* @throws IllegalArgumentException if the argument is not a valid
* reference kind number
*/
public static String referenceKindToString(int referenceKind) {
if (!MethodHandleNatives.refKindIsValid(referenceKind))
throw newIllegalArgumentException("invalid reference kind", referenceKind);
return MethodHandleNatives.refKindName((byte)referenceKind);
}
/**
* Returns a string representation for a {@code MethodHandleInfo},
* given the four parts of its symbolic reference.
* This is defined to be of the form {@code "RK C.N:MT"}, where {@code RK} is the
* {@linkplain #referenceKindToString reference kind string} for {@code kind},
* {@code C} is the {@linkplain java.lang.Class#getName name} of {@code defc}
* {@code N} is the {@code name}, and
* {@code MT} is the {@code type}.
* These four values may be obtained from the
* {@linkplain #getReferenceKind reference kind},
* {@linkplain #getDeclaringClass declaring class},
* {@linkplain #getName member name},
* and {@linkplain #getMethodType method type}
* of a {@code MethodHandleInfo} object.
*
* @implSpec
* This produces a result equivalent to:
* {@code
* String.format("%s %s.%s:%s", referenceKindToString(kind), defc.getName(), name, type)
* }
*
* @param kind the {@linkplain #getReferenceKind reference kind} part of the symbolic reference
* @param defc the {@linkplain #getDeclaringClass declaring class} part of the symbolic reference
* @param name the {@linkplain #getName member name} part of the symbolic reference
* @param type the {@linkplain #getMethodType method type} part of the symbolic reference
* @return a string of the form {@code "RK C.N:MT"}
* @throws IllegalArgumentException if the first argument is not a valid
* reference kind number
* @throws NullPointerException if any reference argument is {@code null}
*/
public static String toString(int kind, Class defc, String name, MethodType type) {
Objects.requireNonNull(name); Objects.requireNonNull(type);
return String.format("%s %s.%s:%s", referenceKindToString(kind), defc.getName(), name, type);
}
}