public interface MethodHandleInfo
Lookup.revealDirect
. ldc
instruction on a CONSTANT_MethodHandle
constant. (See the Java Virtual Machine Specification, sections 4.4.8 and 5.4.3.) Lookup.findVirtual
, to resolve a symbolic reference into a method handle. A symbolic reference consists of a class, name string, and type. Lookup.unreflect
or Lookup.unreflectSpecial
to convert a Method
into a method handle. Lookup.unreflectConstructor
to convert a Constructor
into a method handle. Lookup.unreflectGetter
or Lookup.unreflectSetter
to convert a Field
into a method handle. 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 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 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 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 MethodHandles.reflectAs(java.lang.Class<T>, java.lang.invoke.MethodHandle)
to override this limitation.
reference kind | descriptive name | scope | member | behavior |
---|---|---|---|---|
1 |
REF_getField |
class | FT f; |
(T) this.f; |
2 |
REF_getStatic |
class or interface
|
static FT f;
|
(T) C.f; |
3 |
REF_putField |
class | FT f; |
this.f = x; |
4 |
REF_putStatic |
class |
static FT f;
|
C.f = arg; |
5 |
REF_invokeVirtual |
class | T m(A*); |
(T) this.m(arg*); |
6 |
REF_invokeStatic |
class or interface
|
static T m(A*);
|
(T) C.m(arg*); |
7 |
REF_invokeSpecial |
class or interface
| T m(A*); |
(T) super.m(arg*); |
8 |
REF_newInvokeSpecial |
class | C(A*); |
new C(arg*); |
9 |
REF_invokeInterface |
interface | T m(A*); |
(T) this.m(arg*); |
Modifier and Type | Field | Description |
---|---|---|
static final int |
REF_getField |
A direct method handle reference kind, as defined in the table above. |
static final int |
REF_getStatic |
A direct method handle reference kind, as defined in the table above. |
static final int |
REF_invokeInterface |
A direct method handle reference kind, as defined in the table above. |
static final int |
REF_invokeSpecial |
A direct method handle reference kind, as defined in the table above. |
static final int |
REF_invokeStatic |
A direct method handle reference kind, as defined in the table above. |
static final int |
REF_invokeVirtual |
A direct method handle reference kind, as defined in the table above. |
static final int |
REF_newInvokeSpecial |
A direct method handle reference kind, as defined in the table above. |
static final int |
REF_putField |
A direct method handle reference kind, as defined in the table above. |
static final int |
REF_putStatic |
A direct method handle reference kind, as defined in the table above. |
Modifier and Type | Method | Description |
---|---|---|
Class |
getDeclaringClass() |
Returns the class in which the cracked method handle's underlying member was defined. |
MethodType |
getMethodType() |
Returns the nominal type of the cracked symbolic reference, expressed as a method type. |
int |
getModifiers() |
Returns the access modifiers of the underlying member. |
String |
getName() |
Returns the name of the cracked method handle's underlying member. |
int |
getReferenceKind() |
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. |
default boolean |
isVarArgs() |
Determines if the underlying member was a variable arity method or constructor. |
static String |
referenceKindToString |
Returns the descriptive name of the given reference kind, as defined in the table above. |
<T extends Member> |
reflectAs |
Reflects the underlying member as a method, constructor, or field object. |
static String |
toString |
Returns a string representation for a MethodHandleInfo , given the four parts of its symbolic reference. |
static final int REF_getField
static final int REF_getStatic
static final int REF_putField
static final int REF_putStatic
static final int REF_invokeVirtual
static final int REF_invokeStatic
static final int REF_invokeSpecial
static final int REF_newInvokeSpecial
static final int REF_invokeInterface
int getReferenceKind()
Class<?> getDeclaringClass()
String getName()
MethodType getMethodType()
void
. If it is to a non-static method, the method type will not mention the 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 void
. Note that original direct method handle may include a leading this
parameter, or (in the case of a constructor) will replace the void
return type with the constructed class. The nominal type does not include any this
parameter, and (in the case of a constructor) will return void
.
<T extends Member> T reflectAs(Class<T> expected, MethodHandles.Lookup lookup)
getMethod
, getConstructor
, or getField
. Otherwise, it is reflected as if by getDeclaredMethod
, getDeclaredConstructor
, or getDeclaredField
. The underlying member must be accessible to the given lookup object.T
- the desired type of the result, either Member
or a subtypeexpected
- a class object representing the desired result type T
lookup
- the lookup object that created this MethodHandleInfo, or one with equivalent access privilegesClassCastException
- if the member is not of the expected typeNullPointerException
- if either argument is null
IllegalArgumentException
- if the underlying member is not accessible to the given lookup objectint getModifiers()
default boolean isVarArgs()
getReferenceKind() >= REF_invokeVirtual && Modifier.isTransient(getModifiers())
true
if and only if the underlying member was declared with variable arity.static String referenceKindToString(int referenceKind)
referenceKind
- an integer code for a kind of reference used to access a class member"getField"
IllegalArgumentException
- if the argument is not a valid reference kind number
static String toString(int kind, Class<?> defc, String name, MethodType type)
MethodHandleInfo
, given the four parts of its symbolic reference. This is defined to be of the form "RK C.N:MT"
, where RK
is the reference kind string for kind
, C
is the name of defc
N
is the name
, and MT
is the type
. These four values may be obtained from the reference kind, declaring class, member name, and method type of a MethodHandleInfo
object.
String.format("%s %s.%s:%s", referenceKindToString(kind), defc.getName(), name, type)
kind
- the reference kind part of the symbolic referencedefc
- the declaring class part of the symbolic referencename
- the member name part of the symbolic referencetype
- the method type part of the symbolic reference"RK C.N:MT"
IllegalArgumentException
- if the first argument is not a valid reference kind number
NullPointerException
- if any reference argument is null
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/invoke/MethodHandleInfo.html