- All Known Subinterfaces:
ClassDesc
,DirectMethodHandleDesc
,MethodHandleDesc
,MethodTypeDesc
public interface ConstantDesc
resolveConstantDesc(MethodHandles.Lookup)
to yield the
constant value itself.
Class names in a nominal descriptor, like class names in the constant pool of a classfile, must be interpreted with respect to a particular class loader, which is not part of the nominal descriptor.
Static constants that are expressible natively in the constant pool (String
,
Integer
, Long
, Float
, and Double
) implement
ConstantDesc
, and serve as nominal descriptors for themselves.
Native linkable constants (Class
, MethodType
, and
MethodHandle
) have counterpart ConstantDesc types:
ClassDesc
, MethodTypeDesc
, and MethodHandleDesc
.
Other constants are represented by subtypes of DynamicConstantDesc
.
APIs that perform generation or parsing of bytecode are encouraged to use
ConstantDesc to describe the operand of an ldc
instruction
(including dynamic constants), the static bootstrap arguments of
dynamic constants and invokedynamic
instructions, and other
bytecodes or classfile structures that make use of the constant pool.
Constants describing various common constants (such as ClassDesc
instances for platform types) can be found in ConstantDescs
.
Implementations of ConstantDesc must be value-based classes.
Non-platform classes should not implement ConstantDesc directly.
Instead, they should extend DynamicConstantDesc
(as Enum.EnumDesc
and VarHandle.VarHandleDesc
do.)
Nominal descriptors should be compared using the
Object.equals(Object)
method. There is no guarantee that any
particular entity will always be represented by the same descriptor instance.
- API Note:
- In the future, if the Java language permits, ConstantDesc
may become a
sealed
interface, which would prohibit subclassing except by explicitly permitted types. Clients can assume that the following set of subtypes is exhaustive:String
,Integer
,Long
,Float
,Double
,ClassDesc
,MethodTypeDesc
,MethodHandleDesc
, andDynamicConstantDesc
; this list may be extended to reflect future changes to the constant pool format as defined in JVMS 4.4. - See Java Virtual Machine Specification:
-
4.4 The Constant Pool
- Since:
- 12
- See Also:
Constable
,ConstantDescs
-
Method Summary
Modifier and TypeMethodDescriptionresolveConstantDesc(MethodHandles.Lookup lookup)
Resolves this descriptor reflectively, emulating the resolution behavior of JVMS 5.4.3 and the access control behavior of JVMS 5.4.4.
-
Method Details
-
resolveConstantDesc
Resolves this descriptor reflectively, emulating the resolution behavior of JVMS 5.4.3 and the access control behavior of JVMS 5.4.4. The resolution and access control context is provided by theMethodHandles.Lookup
parameter. No caching of the resulting value is performed.- API Note:
- MethodTypeDesc can represent method type descriptors that are not representable by MethodType, such as methods with more than 255 parameter slots, so attempts to resolve these may result in errors.
- Parameters:
lookup
- TheMethodHandles.Lookup
to provide name resolution and access control context- Returns:
- the resolved constant value
- Throws:
ReflectiveOperationException
- if a class, method, or field could not be reflectively resolved in the course of resolutionLinkageError
- if a linkage error occurs- See Java Virtual Machine Specification:
-
5.4.3 Resolution
5.4.4 Access Control
-