Reflection question: Why is length not a field of an array?

[Ian A. Mason]

The Java Language Specification says (10.7 page 197)

"The members of an array type are all of the following"

* The public final field length ...
* The public method clone which overrides ...
* All the members inherited from the class Object; ...

....

"

Yet if one tries to access that field via reflection, it isn't there.
(Nor is the public clone method that is supposed to be there.)
It seems only to be accessible via the Array.getLength method. Any
*real* reason for this? For doubting thomases:

import java.lang.reflect.Field;
import java.lang.reflect.Array;
import java.lang.reflect.Method;

public class ArrayLength {
public static void main(String[] args){
Object target = new int[10];
Class targetClass = target.getClass();
Field field;
try {
field = targetClass.getField("length");
}catch(NoSuchFieldException e){
System.err.println("No such field: " + e);
}catch(SecurityException e){
System.err.println("Security exception: " + e);
}
/* look for the length field */
Field[] fields = targetClass.getFields();
System.err.println("fields.length = " + fields.length);
/* nope */
/* OK get it the other way */
System.err.println("array length = " + Array.getLength(target));
/* what about the methods inherited from Object */
Method[] methods = targetClass.getMethods();
System.err.println("methods.length = " + methods.length);
/* OK looks right */
/* a public clone is supposed to be here as well */
Method[] dmethods = targetClass.getDeclaredMethods();
System.err.println("declared methods.length = " + dmethods.length);
/* nope not there either */
}
}

 

[Tor Iver Wilhelmsen]

Yet if one tries to access that field via reflection, it isn't there.

Correct: The "Java-the-language" array length "field" is turned into a
call to the "Java-the-VM" instruction arraylength.

In effect, it's syntactic sugar, much like the Foo.class "static
field" which does not exist either (though the compiler will
synthesize a method class$(String) which wraps a call to
Class.forName()).

 

[Chris Uppal]

Correct: The "Java-the-language" array length "field" is turned into a
call to the "Java-the-VM" instruction arraylength.

In effect, it's syntactic sugar

Yes, and a bloody stupid idea too...

-- chris