public class MethodHandleProxies extends Object
| Modifier and Type | Method and Description |
|---|---|
static <T> T |
asInterfaceInstance(Class<T> intfc,
MethodHandle target)
Produces an instance of the given single-method interface which redirects
its calls to the given method handle.
|
static boolean |
isWrapperInstance(Object x)
Determines if the given object was produced by a call to
asInterfaceInstance. |
static MethodHandle |
wrapperInstanceTarget(Object x)
Produces or recovers a target method handle which is behaviorally
equivalent to the unique method of this wrapper instance.
|
static Class<?> |
wrapperInstanceType(Object x)
Recovers the unique single-method interface type for which this wrapper instance was created.
|
public static <T> T asInterfaceInstance(Class<T> intfc, MethodHandle target)
A single-method interface is an interface which declares a uniquely named method.
When determining the uniquely named method of a single-method interface,
the public Object methods (toString, equals, hashCode)
are disregarded. For example, Comparator is a single-method interface,
even though it re-declares the Object.equals method.
The interface must be public. No additional access checks are performed.
The resulting instance of the required type will respond to
invocation of the type's uniquely named method by calling
the given target on the incoming arguments,
and returning or throwing whatever the target
returns or throws. The invocation will be as if by
target.invoke.
The target's type will be checked before the
instance is created, as if by a call to asType,
which may result in a WrongMethodTypeException.
The uniquely named method is allowed to be multiply declared,
with distinct type descriptors. (E.g., it can be overloaded,
or can possess bridge methods.) All such declarations are
connected directly to the target method handle.
Argument and return types are adjusted by asType
for each individual declaration.
The wrapper instance will implement the requested interface
and its super-types, but no other single-method interfaces.
This means that the instance will not unexpectedly
pass an instanceof test for any unrequested type.
Implementation Note:
Therefore, each instance must implement a unique single-method interface.
Implementations may not bundle together
multiple single-method interfaces onto single implementation classes
in the style of AWTEventMulticaster.
The method handle may throw an undeclared exception,
which means any checked exception (or other checked throwable)
not declared by the requested type's single abstract method.
If this happens, the throwable will be wrapped in an instance of
UndeclaredThrowableException
and thrown in that wrapped form.
Like Integer.valueOf,
asInterfaceInstance is a factory method whose results are defined
by their behavior.
It is not guaranteed to return a new instance for every call.
Because of the possibility of bridge methods
and other corner cases, the interface may also have several abstract methods
with the same name but having distinct descriptors (types of returns and parameters).
In this case, all the methods are bound in common to the one given target.
The type check and effective asType conversion is applied to each
method type descriptor, and all abstract methods are bound to the target in common.
Beyond this type check, no further checks are made to determine that the
abstract methods are related in any way.
Future versions of this API may accept additional types, such as abstract classes with single abstract methods. Future versions of this API may also equip wrapper instances with one or more additional public "marker" interfaces.
If a security manager is installed, this method is caller sensitive. During any invocation of the target method handle via the returned wrapper, the original creator of the wrapper (the caller) will be visible to context checks requested by the security manager.
T - the desired type of the wrapper, a single-method interfaceintfc - a class object representing Ttarget - the method handle to invoke from the wrapperNullPointerException - if either argument is nullIllegalArgumentException - if the intfc is not a
valid argument to this methodWrongMethodTypeException - if the target cannot
be converted to the type required by the requested interfacepublic static boolean isWrapperInstance(Object x)
asInterfaceInstance.x - any referenceasInterfaceInstancepublic static MethodHandle wrapperInstanceTarget(Object x)
x must have been produced by a call to asInterfaceInstance.
This requirement may be tested via isWrapperInstance.x - any referenceIllegalArgumentException - if the reference x is not to a wrapper instancepublic static Class<?> wrapperInstanceType(Object x)
x must have been produced by a call to asInterfaceInstance.
This requirement may be tested via isWrapperInstance.x - any referenceIllegalArgumentException - if the reference x is not to a wrapper instance Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright © 1993, 2015, Oracle and/or its affiliates. All rights reserved.