ConstantCallSite

public class ConstantCallSite
extends CallSite

java.lang.Object
   ↳ java.lang.invoke.CallSite
     ↳ java.lang.invoke.ConstantCallSite


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.

Summary

Public constructors

ConstantCallSite(MethodHandle target)

Creates a call site with a permanent target.

Protected constructors

ConstantCallSite(MethodType targetType, MethodHandle createTargetHook)

Creates a call site with a permanent target, possibly bound to the call site itself.

Public methods

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(MethodHandle ignore)

Always throws an UnsupportedOperationException.

Inherited methods

Public constructors

ConstantCallSite

added in API level 26
public ConstantCallSite (MethodHandle target)

Creates a call site with a permanent target.

Parameters
target MethodHandle: the target to be permanently associated with this call site

Throws
NullPointerException if the proposed target is null

Protected constructors

ConstantCallSite

added in API level 26
protected ConstantCallSite (MethodType targetType, 
                MethodHandle createTargetHook)

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 MethodType: the type of the method handle to be permanently associated with this call site

createTargetHook MethodHandle: 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

Public methods

dynamicInvoker

added in API level 26
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.

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

Throws
IllegalStateException if the ConstantCallSite constructor has not completed

getTarget

added in API level 26
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.

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

Throws
IllegalStateException if the ConstantCallSite constructor has not completed

setTarget

added in API level 26
public final void setTarget (MethodHandle ignore)

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

Parameters
ignore MethodHandle: a new target proposed for the call site, which is ignored

Throws
UnsupportedOperationException because this kind of call site cannot change its target