Enthuware

The option 2, is misguiding,

You can set the Locale after constructing a DateFormat or a NumberFormat object and before using it to do country specific formatting.

we can actually, set the default local, calling, Locale.setDefault(Locale.US)

1. NumberFormat f = NumberFormat.getInstance();
2. Locale.setDefault(Locale.Category.FORMAT,Locale.US)
3. f.format(23456.56);

The first line formatter, will be always impacted by the line 2,
NumberFormat f = NumberFormat.getInstance(Locale.US);, this shall not get impacted by, the second line.

EDIT:
Hi, I tried the thing, it does not seem, to work,
The instance returned, in the 1st line does not seem to get impacted, by the second line.

You are changing the default locale. You are not changing the locale of NumberFormat.
But the case that you have highlighted is definitely interesting to know. I haven't tested it out though.

Hi, I tried the thing, it does not seem, to work,
The instance returned, in the 1st line does not seem to get impacted, by the second line.