EXECUTION

Finalization of Class Instances

12.6

class Test extends Super {

int indiana = (int)Math.PI;

//

That is,

3

public static void main(String[] args) {

Test t = new Test();

t.printThree();

}

void printThree() { System.out.println(indiana); }

}

produces the output:

0

3

This shows that the invocation of

printThree

 in the constructor for class

Super

does not invoke the definition of

printThree

 in class

Super

, but rather invokes

the overriding definition of

printThree

 in class

Test

. This method therefore

runs before the field initializers of

Test

 have been executed, which is why the first

value output is

0

, the default value to which the field

three

 of

Test

 is initialized.

The later invocation of

printThree

 in method

main

 invokes the same definition

of

printThree

, but by that point the initializer for instance variable

three

 has

been executed, and so the value

3

 is printed.

See  8.6 for more details on constructor declarations.

12.6   Finalization of Class Instances

The class

Object

 has a

protected

 method called

finalize

( 20.1.11); this

method can be overridden by other classes. The particular definition of

finalize

that can be invoked for an object is called the

finalizer

 of that object. Before the

storage for an object is reclaimed by the garbage collector, the Java Virtual

Machine will invoke the finalizer of that object.

Finalizers provide a chance to free up resources (such as file descriptors or

operating system graphics contexts) that cannot be freed automatically by an auto 

matic storage manager. In such situations, simply reclaiming the memory used by

an object would not guarantee that the resources it held would be reclaimed.

The Java language does not specify how soon a finalizer will be invoked,

except to say that it will happen before the storage for the object is reused. Also,

the Java language does not specify which thread will invoke the finalizer for any

given object. If an uncaught exception is thrown during the finalization, the excep 

tion is ignored and finalization of that object terminates.

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