EXECUTION

Resolution of Symbolic References

12.3.3

12.3.2   Preparation of a Class or Interface Type

Preparation

 involves creating the

static

 fields (class variables and constants) for

a class or interface and initializing such fields to the standard default values

( 4.5.4). This does not require the execution of any Java code; explicit initializers

for

static

 fields are executed as part of initialization ( 12.4), not preparation.

Java implementations must detect the following error during preparation:

AbstractMethodError

: A class that is not declared to be

abstract

 has an

abstract

 method. This can occur, for example, if a method that is originally

not

abstract

 is changed to be

abstract

 after another class that inherits the

now

abstract

 method declaration has been compiled ( 13.4.15).

If such an error is detected, then an instance of

AbstractMethodError

 should be

thrown at the point in the Java program that caused the class to be prepared.

Implementations of the Java Virtual Machine may precompute additional data

structures at preparation time in order to make later operations on a class or inter 

face more efficient. One particularly useful data structure is a  method table  or

other data structure that allows any method to be invoked on instances of a class

without requiring a search of superclasses at invocation time.

12.3.3   Resolution of Symbolic References

A Java binary file references other classes and interfaces and their fields, methods,

and constructors symbolically, using the fully qualified names of the other classes

and interfaces ( 13.1). For fields and methods, these symbolic references include

the name of the class or interface type that declares the field or method as well as

the name of the field or method itself, together with appropriate type information.

Before a symbolic reference can be used it must be undergo

resolution

,

wherein a symbolic reference is checked to be correct and, typically, replaced with

a direct reference that can be more efficiently processed if the reference is used

repeatedly.

If an error occurs during resolution, then an error will be thrown. Most typi 

cally, this will be an instance of one of the following subclasses of the class

IncompatibleClassChangeError

, but it may also be an instance of some other

subclass of

IncompatibleClassChangeError

 or even an instance of the class

IncompatibleClassChangeError

 itself. This error may be thrown at any point

in the program that uses a symbolic reference to the type, directly or indirectly:

IllegalAccessError

: A symbolic reference has been encountered that

specifies a use or assignment of a field, or invocation of a method, or creation

of an instance of a class, to which the code containing the reference does not

have access because the field or method was declared

private

,

protected

,

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