15.11.4

Runtime Evaluation of Method Invocation

EXPRESSIONS

( 15.11.3), then this is the method to be invoked, and the procedure terminates.

(We note that as part of the loading and linking process that the virtual machine

checks that an overriding method is at least as accessible as the overridden

method; an

IncompatibleClassChangeError

 occurs if this is not the case.)

2. Otherwise, if

S

 is not

T

, this same lookup procedure is performed using the

superclass of

S

; whatever it comes up with is the result of this lookup.

This procedure will find a suitable method when it reaches class

T

, because other 

wise an

IllegalAccessError

 would have been thrown by the checks of the pre 

vious section  15.11.4.3.

We note that the dynamic lookup process, while described here explicitly, will

often be implemented implicitly, for example as a side effect of the construction

and use of per class method dispatch tables, or the construction of other per class

structures used for efficient dispatch.

15.11.4.5

Create Frame, Synchronize, Transfer Control

A method

m

 in some class

S

 has been identified as the one to be invoked.

Now a new

activation frame

 is created, containing the target reference (if any)

and the argument values (if any), as well as enough space for the local variables

and stack for the method to be invoked and any other bookkeeping information

that may be required by the implementation (stack pointer, program counter, refer 

ence to previous activation frame, and the like). If there is not sufficient memory

available to create such an activation frame, an

OutOfMemoryError

 is thrown.

The newly created activation frame becomes the current activation frame. The

effect of this is to assign the argument values to corresponding freshly created

parameter variables of the method, and to make the target reference available as

this

, if there is a target reference.

If the method

m

 is a

native

 method but the necessary native, implementation 

dependent binary code has not been loaded ( 20.16.14,  20.16.13) or otherwise

cannot be dynamically linked, then an

UnsatisfiedLinkError

 is thrown.

If the method

m

 is not

synchronized

, control is transferred to the body of the

method

m

 to be invoked.

If the method

m

 is

synchronized

, then an object must be locked before the

transfer of control. No further progress can be made until the current thread can

obtain the lock. If there is a target reference, then the target must be locked; other 

wise the

Class

 object for class

S

, the class of the method

m

, must be locked. Con 

trol is then transferred to the body of the method

m

 to be invoked. The object is

automatically unlocked when execution of the body of the method has completed,

whether normally or abruptly. The locking and unlocking behavior is exactly as if

the body of the method were embedded in a

synchronized

 statement ( 14.17).

336