Hi Peepers, I feel like I answered this already but someone tagged me (thanks,
@BirdWorld !) so I will try to help you. Let me know if you already heard from me.
First - think about what 'aggressive' means and what you can tolerate. As far as I know, Java finches don't maim other birds or anything like that. "Get away from me" is usually just done by opening the beak, you've probably seen that already. Two java males may fight, so you do need to be sure you know whether yours is a male or a female. And of course cage size comes into play, as does out-of-cage time. Meaning the more room they have the less they'll fight. If they are guarding food, just put a second feeder in so they each have their own. I actually put in 3 sometimes, so there's no hope of one getting left out. There are other tricks as well, like hanging visual barriers so they don't see each other as much. I don't mind squabbling, as long as there's no injury.
Next - that video was about 2 completely different species than yours. I didn't see the aggression, other than the beak opening. I did see a size difference, and I probably would not have put the canary with the goldfinch myself. You could put yours with another Java, or a gray singer - or even a diamond firetail! Have you seen them?
But if it was me, I'd get a fellow Java. Definitely do not put a smaller, more laid back finch with Peepers. That's where people run into trouble!
Third, this is just my opinion but I think it's kind of cruel to keep finches as singles. They're flock birds and they need their flock. We can try, but we're not really a good substitute for someone that speaks their language.
That said, I haven't heard what you have about separating them due to aggression. I know quite a few people that raise them. I would bet that it comes down to cage size/flying room. Anyway, if you have Peepers hand tamed and after reading all this you still feel reluctant to get him a companion -- there's nothing wrong with that. He looks like he enjoys Youtube birds!
