Shuffling a JSON array in Java
It runs in \$O(n)\$ time so I'm not sure there's a way to improve this.  It looks like you've implemented the algorithm pretty well, according the Fisher-Yates shuffle.

You might consider not using Object if you can use the type that's stored in the array instead.

I also thought I read somewhere that it should be safe to loop to \$n/2\$ instead of \$n\$ (because you're swapping with elements from \$1 \cdots n\$ so in theory, you shouldn't need to swap every element), but I don't have hard proof of that, so you take your chances ;)