12.3.4

Linking: Implications for Code Generation

EXECUTION

or default access (not

public

), or because the class was not declared

public

.

This can occur, for example, if a field that is originally declared

public

 is

changed to be

private

 after another class that refers to the field has been

compiled ( 13.4.6).

InstantiationError

: A symbolic reference has been encountered that is

used in a class instance creation expression, but an instance cannot be created

because the reference turns out to refer to an interface or to an

abstract

class. This can occur, for example, if a class that is originally not

abstract

 is

changed to be

abstract

 after another class that refers to the class in question

has been compiled ( 13.4.1).

NoSuchFieldError

: A symbolic reference has been encountered that refers

to a specific field of a specific class or interface, but the class or interface does

not declare a field of that name (it is specifically not sufficient for it simply to

be an inherited field of that class or interface). This can occur, for example, if

a field declaration was deleted from a class after another class that refers to

the field was compiled ( 13.4.7).

NoSuchMethodError

: A symbolic reference has been encountered that refers

to a specific method of a specific class or interface, but the class or interface

does not declare a method of that signature (it is specifically not sufficient for

it simply to be an inherited method of that class or interface). This can occur,

for example, if a method declaration was deleted from a class after another

class that refers to the method was compiled ( 13.4.12).

Additionally, an

UnsatisfiedLinkError

 (a subclass of

LinkageError

)

may be thrown if a class declares a

native

 method for which no implementation

can be found. The error will occur if the method is used, or earlier depending on

what kind of resolution strategy is being used by the virtual machine ( 12.3).

12.3.4   Linking: Implications for Code Generation

The symbolic references within a group of types may be resolved even before the

group is loaded ( 12.2.2), in an implementation that uses a special (non standard)

binary format ( 13.1). This corresponds to the traditional practice of  linkage

editing.  Even if this is not done, a Java implementation has a lot of flexibility. It

may resolve all symbolic references from a type at the point of the first linkage

activity on the type, or defer the resolution of each symbolic reference to the first

use of that reference.

We note that the flexibility accorded the Java implementation in the linkage

process does not affect correctly formed Java programs, which should never

encounter linkage errors.

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