Curious about "If" in Java

How many conditional statements can an if check for? EG,

if(a==1 && b==1 && c==1 && ... && n==1)

I know this could probably be solved simply by nesting ifs and then it wouldn't be an issue how many. But frankly, I'm curious and can't seem to find how many it will take.

In addition, since I have your attention anyway, is there any difference in efficiency between

if(a==1 && b ==1)

And

if(a==1)
    if(b==1)