Depends on what your goals are for your breeding program. If it doesn't have decent Java *type*, then I wouldn't bother with it at all - put it into your food-egg flock or eat it.
If you are breeding your Mottleds to the Standard, then you do not want to use that bird. Mottled Javas already have more white in them than the SOP calls for (with individual differences in white amounts). Mottleds also get whiter with age. Even if that white bird were to have correct body type and other correct Java characteristics, if you add that white bird into your Mottled breeding program, you could add in way too much white into the Mottleds. White is something that needs to be toned down in most Mottleds and it's a struggle to try to get the number of all-white feathers out of the wings and tails especially.
If the bird turns out to have correct Java type and other characteristics once it is fully matured (usually at least a year for females, males can take a couple of years to be fully matured to where they will not change much except to have their white feathering increase over time), then you could look at breeding it as a White Java if you desired.
There is no SOP for the White Java because they are no longer recognized as a variety. The problem with the White Javas was the leg/foot color. The Standard for the Whites, which it seems was not officially disseminated in print, forced the Java breeders to make changes to their White Javas in order for them to look different from White Rocks. The APA wanted the White Javas to have willow (greeny-blackish color) legs. However in the old literature, the breeders say that the White Javas should have yellow legs, not willow legs. And that SOP for White Javas is 100+ years old. So you would have to decide what color legs you were going to try breeding for and whether or not you wanted to try to go for the willow color which the APA recognized, or the yellow legs that the breeders in the late 18th/early 19th century said was correct for them. It was apparently difficult for enough White Javas to get the willow leg color, which is why they died out and were removed from the Standard.
Beyond the leg color issue, if you were to try to breed the White, I would say to breed them to the Java SOP for the non-color characteristics, and then make your choice as to what leg color you want. I don't recall if I have found anything in the old literature yet about what the correct eye color for the White Java was supposed to be. If the bird doesn't have good Java type, you can breed it but it will probably be a really long while (if at all) before you get offspring that have the correct *Java look*, rather than just the generic white chicken silhouette.
If you decided to breed the White bird, if you have good Java type, you're still going to be fighting with black feathering for a while in the offspring. I would say to pick the best typed Mottleds that have the most amount of white in them when they are young, to breed to the White bird first. But you may have to hatch some pretty large amounts of chicks for a few years to try to get more white birds to breed with, as well as to maintain the other Java characteristics.
It would not be a project for the faint of heart. It's a lot of hard work and frustration just trying to improve/maintain the proper characteristics in the Blacks and Mottleds.
