ConstantCallSite
is a CallSite
whose target is permanent, and can never be changed.
An invokedynamic
instruction linked to a ConstantCallSite
is permanently
bound to the call site's target.- Since:
- 1.7
-
Constructor Summary
ModifierConstructorDescriptionConstantCallSite
(MethodHandle target) Creates a call site with a permanent target.protected
ConstantCallSite
(MethodType targetType, MethodHandle createTargetHook) Creates a call site with a permanent target, possibly bound to the call site itself. -
Method Summary
Modifier and TypeMethodDescriptionfinal MethodHandle
Returns this call site's permanent target.final MethodHandle
Returns the target method of the call site, which behaves like afinal
field of theConstantCallSite
.final void
setTarget
(MethodHandle ignore) Always throws anUnsupportedOperationException
.
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Constructor Details
-
ConstantCallSite
Creates a call site with a permanent target.- Parameters:
target
- the target to be permanently associated with this call site- Throws:
NullPointerException
- if the proposed target is null
-
ConstantCallSite
Creates a call site with a permanent target, possibly bound to the call site itself.During construction of the call site, the
createTargetHook
is invoked to produce the actual target, as if by a call of the form(MethodHandle) createTargetHook.invoke(this)
.Note that user code cannot perform such an action directly in a subclass constructor, since the target must be fixed before the
ConstantCallSite
constructor returns.The hook is said to bind the call site to a target method handle, and a typical action would be
someTarget.bindTo(this)
. However, the hook is free to take any action whatever, including ignoring the call site and returning a constant target.The result returned by the hook must be a method handle of exactly the same type as the call site.
While the hook is being called, the new
ConstantCallSite
object is in a partially constructed state. In this state, a call togetTarget
, or any other attempt to use the target, will result in anIllegalStateException
. It is legal at all times to obtain the call site's type using thetype
method.- Parameters:
targetType
- the type of the method handle to be permanently associated with this call sitecreateTargetHook
- a method handle to invoke (on the call site) to produce the call site's target- Throws:
WrongMethodTypeException
- if the hook cannot be invoked on the required arguments, or if the target returned by the hook is not of the giventargetType
NullPointerException
- if the hook returns a null valueClassCastException
- if the hook returns something other than aMethodHandle
Throwable
- anything else thrown by the hook function
-
-
Method Details
-
getTarget
Returns the target method of the call site, which behaves like afinal
field of theConstantCallSite
. That is, the target is always the original value passed to the constructor call which created this instance.- Specified by:
getTarget
in classCallSite
- Returns:
- the immutable linkage state of this call site, a constant method handle
- Throws:
IllegalStateException
- if theConstantCallSite
constructor has not completed- See Also:
-
setTarget
Always throws anUnsupportedOperationException
. This kind of call site cannot change its target.- Specified by:
setTarget
in classCallSite
- Parameters:
ignore
- a new target proposed for the call site, which is ignored- Throws:
UnsupportedOperationException
- because this kind of call site cannot change its target- See Also:
-
dynamicInvoker
Returns this call site's permanent target. Since that target will never change, this is a correct implementation ofCallSite.dynamicInvoker
.- Specified by:
dynamicInvoker
in classCallSite
- Returns:
- the immutable linkage state of this call site, a constant method handle
- Throws:
IllegalStateException
- if theConstantCallSite
constructor has not completed
-