JLS tweaks

Archie Cobbs archie at dellroad.org
Thu Mar 13 22:00:42 UTC 2014

On Thu, Mar 13, 2014 at 5:21 AM, Peter Levart <peter.levart at gmail.com>wrote:

> On 03/13/2014 11:08 AM, Peter Levart wrote:
>> I don't see this as any more complex or unsafe as the rules for final
>> fields. But I don't know if it is compatible with JVM rules.
> Does JVM have any rules for final instance fields regarding their
> definitive assignment at all non-exceptional exit paths of the constructor?

My understanding is that the JVM doesn't care how many times you assign a
final field in a constructor, it only cares that you don't try to assign it
from within a non-constructor method. See also this stackoverflow

Note also that the JVM spec specifically allows a constructor to assign
final fields before invoking super()/this(). So if the proposal we are
talking about were implemented, it should probably also allow this. So for
example this would be legal:

public class SetOfInts extends HashSet<Integer> {

    private final int max;

    public SetOfInts(int max) {
        this.max = max;   // the only thing you can do with 'this' here
        final Integer[] array = new Integer[max];
        for (int i = 0; i < max; i++)
            array[i] = i;


Archie L. Cobbs
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