Module java.base

Class ConstantCallSite

  • 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.
    • Constructor Detail

      • ConstantCallSite

        public ConstantCallSite​(MethodHandle target)
        Creates a call site with a permanent target.
        target - the target to be permanently associated with this call site
        NullPointerException - if the proposed target is null
      • ConstantCallSite

        protected 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 site
        createTargetHook - a method handle to invoke (on the call site) to produce the call site's target
        WrongMethodTypeException - 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 value
        ClassCastException - if the hook returns something other than a MethodHandle
        Throwable - anything else thrown by the hook function