EXECUTION

Initialize

Test

: Execute Initializers

12.1.3

a.out

  file that contains a fully linked version of the program, including com 

pletely resolved links to library routines used by the program. Copies of these

library routines are included in the  

a.out

  file.)

An implementation may instead choose to resolve a symbolic reference only

when it is actively used; consistent use of this strategy for all symbolic references

would represent the  laziest  form of resolution. In this case, if

Test

 had several

symbolic references to another class, then the references might be resolved one at

a time, as they are used, or perhaps not at all, if these references were never used

during execution of the program.

The only requirement on when resolution is performed is that any errors

detected during resolution must be thrown at a point in the program where some

action is taken by the program that might, directly or indirectly, require linkage to

the class or interface involved in the error. Using the  static  example implemen 

tation choice described above, loading and linkage errors could occur before the

program is executed if they involved a class or interface mentioned in the class

Test

 or any of the further, recursively referenced, classes and interfaces. In a

system that implemented the  laziest  resolution, these errors would be thrown

only when an incorrect symbolic reference is actively used.

The resolution process is described further in  12.3.3.

12.1.3   Initialize

Test

: Execute Initializers

In our continuing example, the virtual machine is still trying to execute the

method

main

 of class

Test

. This is an attempted active use ( 12.4.1) of the class,

which is permitted only if the class has been initialized.

Initialization consists of execution of any class variable initializers and static

initializers of the class

Test

, in textual order. But before

Test

 can be initialized,

its direct superclass must be initialized, as well as the direct superclass of its direct

superclass, and so on, recursively. In the simplest case,

Test

 has

Object

 as its

implicit direct superclass; if class

Object

 has not yet been initialized, then it must

be initialized before

Test

 is initialized. Class

Object

 has no superclass, so the

recursion terminates here.

If class

Test

 has another class

Super

 as its superclass, then

Super

 must be

initialized before

Test

. This requires loading, verifying, and preparing

Super

 if

this has not already been done and, depending on the implementation, may also

involve resolving the symbolic references from

Super

 and so on, recursively.

Initialization may thus cause loading, linking, and initialization errors, includ 

ing such errors involving other types.

The initialization process is described further in  12.4.

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