Grit for your Java's
As Java's are a seed eating bird a vital part of their diet is grit. Why! Because they have no teeth, grit is held in the organ known as the gizzard and grinds the seed, to help break it down as part of their digestive system. I have kept budgies in the past and have also put grit out for them to eat, I don't know why but Java's seem to eat grit more than the budgies ever did.
There are two different types of grit you can use: oyster shell obviously from a shell, (lime) this type of grit is known as soluble that dissolves readily in the acid conditions of the Java's gizzard and provides a useful source of minerals and is past through the digestive system after some time. Mineral grit (quartz), insoluble, it's sharp edges grind at the seeds better in the thick muscular walls of the gizzard, you need to ensure both types of grit are on offer at all times. My Java's are constantly picking bits out of the earth in the outdoor flight

I offer grit in small round containers. You can put different types of grit in separate containers if you like or as I do mix the two together, I have watched the Java's to see if one type of grit is favoured more than the other, my conclusion after endless hours is NO! one is not favoured more than the other. Give the containers a shake up every so often to mix the grit up as the Java's pick the best bits off the top.

Bird sand that some people use on the cage or aviary floors contains small white bits of oyster shell.

Captive birds can not get this needed part of their diet freely its up to you the bird keeper to provide it for them.