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

From class


        
          java.lang.invoke.CallSite

`abstract MethodHandle`	`dynamicInvoker()` Produces a method handle equivalent to an invokedynamic instruction which has been linked to this call site.
`abstract MethodHandle`	`getTarget()` Returns the target method of the call site, according to the behavior defined by this call site's specific class.
`abstract void`	`setTarget(MethodHandle newTarget)` Updates the target method of this call site, according to the behavior defined by this call site's specific class.
`MethodType`	`type()` Returns the type of this call site's target.

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

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