Java compact1, compact2, compact3 java.lang.invoke Class ConstantCallSite（JDK8）

Constructor Detail

• ConstantCallSite

  public ConstantCallSite(MethodHandle target)

  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

  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.

  Parameters:

  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

  Throws:

  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

Method Detail

• getTarget

  public 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.

  Specified by:

  getTarget in class CallSite

  Returns:

  the immutable linkage state of this call site, a constant method handle

  Throws:

  IllegalStateException - if the ConstantCallSite constructor has not completed

  See Also:

  ConstantCallSite, VolatileCallSite, CallSite.setTarget(java.lang.invoke.MethodHandle), getTarget(), MutableCallSite.getTarget(), VolatileCallSite.getTarget()

• setTarget

  public final void setTarget(MethodHandle ignore)

  Always throws an UnsupportedOperationException. This kind of call site cannot change its target.

  Specified by:

  setTarget in class CallSite

  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:

  CallSite.getTarget(), setTarget(java.lang.invoke.MethodHandle), MutableCallSite.setTarget(java.lang.invoke.MethodHandle), VolatileCallSite.setTarget(java.lang.invoke.MethodHandle)

• dynamicInvoker

  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.

  Specified by:

  dynamicInvoker in class CallSite

  Returns:

  the immutable linkage state of this call site, a constant method handle

  Throws:

  IllegalStateException - if the ConstantCallSite constructor has not completed