public non-sealed class ConstantCallSite extends CallSite
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.Modifier | Constructor | Description |
---|---|---|
Creates a call site with a permanent target. |
||
protected |
Creates a call site with a permanent target, possibly bound to the call site itself. |
Modifier and Type | Method | Description |
---|---|---|
final MethodHandle |
dynamicInvoker() |
Returns this call site's permanent target. |
final MethodHandle |
getTarget() |
Returns the target method of the call site, which behaves like a final field of the ConstantCallSite . |
final void |
setTarget |
Always throws an UnsupportedOperationException . |
public ConstantCallSite(MethodHandle target)
target
- the target to be permanently associated with this call siteNullPointerException
- if the proposed target is nullprotected ConstantCallSite(MethodType targetType, MethodHandle createTargetHook) throws Throwable
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 to getTarget
, or any other attempt to use the target, will result in an IllegalStateException
. It is legal at all times to obtain the call site's type using the type
method.
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 targetWrongMethodTypeException
- if the hook cannot be invoked on the required arguments, or if the target returned by the hook is not of the given targetType
NullPointerException
- if the hook returns a null valueClassCastException
- if the hook returns something other than a MethodHandle
Throwable
- anything else thrown by the hook functionpublic final MethodHandle getTarget()
final
field of the ConstantCallSite
. That is, the target is always the original value passed to the constructor call which created this instance.getTarget
in class CallSite
IllegalStateException
- if the ConstantCallSite
constructor has not completedpublic final void setTarget(MethodHandle ignore)
UnsupportedOperationException
. This kind of call site cannot change its target.setTarget
in class CallSite
ignore
- a new target proposed for the call site, which is ignoredUnsupportedOperationException
- because this kind of call site cannot change its targetpublic final MethodHandle dynamicInvoker()
CallSite.dynamicInvoker
.dynamicInvoker
in class CallSite
IllegalStateException
- if the ConstantCallSite
constructor has not completed
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/invoke/ConstantCallSite.html