Module java.base

Package java.lang.constant

Interface ConstantDesc

All Known Subinterfaces:

ClassDesc, DirectMethodHandleDesc, MethodHandleDesc, MethodTypeDesc

All Known Implementing Classes:

Double, DynamicConstantDesc, Enum.EnumDesc, Float, Integer, Long, String, VarHandle.VarHandleDesc

public interface ConstantDesc

A nominal descriptor for a loadable constant value, as defined in JVMS 4.4. Such a descriptor can be resolved via 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 to a 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.

Since:

12

See Also:

Constable, ConstantDescs

Method Summary

Modifier and Type	Method	Description
Object	resolveConstantDesc(MethodHandles.Lookup lookup)	Resolve this descriptor reflectively, emulating the resolution behavior of JVMS 5.4.3 and the access control behavior of JVMS 5.4.4.

Method Detail

resolveConstantDesc

Object resolveConstantDesc(MethodHandles.Lookup lookup)
                    throws ReflectiveOperationException

Resolve 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 the MethodHandles.Lookup parameter. No caching of the resulting value is performed.

Parameters:

lookup - The MethodHandles.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 resolution

LinkageError - if a linkage error occurs