Javas are very social birds and like to be in a group. So you can keep more than 1 pair in a large cage together. But for breeding, you should keep only 1 pair per cage or there will be fighting. If you don't want to breed them, just don't put in any nest boxes.
You can colony breed Javas in a large
aviary.
RigorMortisKitten, 4 (or even 6) Javas would probably be fine in the cage you posted a photo of - but that is too small to breed 2 pairs together (they will probably fight).
Here are some photos of my pet Javas, from the past... they can be tamed if you start out with very young ones and really work at it. But adult birds are pretty much untameable. I wrote an article about taming them.
I had this trio back in the 1990s. I got them as fledgelings and worked hard to tame them. They were very tame and would fly to me whenever I called them. I could let them fly in my screened porch in the summer.
Wild Java Sparrows in Hawaii. There are huge flocks of them in Hawaii. They were introduced there from Asia.
Will they not do good in single pairs ?
I was thinking about having just males or just females though, since i dont want any babies!
