public class ConstantCallSite extends CallSite
A 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.
public ConstantCallSite(MethodHandle target)
Creates a call site with a permanent 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 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 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()
Returns the target method of the call site, which behaves like a 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 completedConstantCallSite, VolatileCallSite, CallSite.setTarget(java.lang.invoke.MethodHandle), getTarget(), MutableCallSite.getTarget(), VolatileCallSite.getTarget()
public final void setTarget(MethodHandle ignore)
Always throws an 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 targetCallSite.getTarget(), setTarget(java.lang.invoke.MethodHandle), MutableCallSite.setTarget(java.lang.invoke.MethodHandle), VolatileCallSite.setTarget(java.lang.invoke.MethodHandle)
public final MethodHandle dynamicInvoker()
Returns this call site's permanent target. Since that target will never change, this is a correct implementation of CallSite.dynamicInvoker.
dynamicInvoker in class CallSite
IllegalStateException - if the ConstantCallSite constructor has not completed
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