Standards or best practises for Java imports?

Question

I was just wondering how some of the more seasoned developers out there handle Java imports. I'm fairly new to Java programming and as far as I know there is very little difference between explicitly importing individual classes and importing entire packages, other than at compilation time on large projects, however I'm wondering if there is an official standard or if you have any personal preferences for it.
Personally I always used to import packages unless I was only using one class from the package, however I have a friend who swears by importing individual classes for everything you use unless you are using almost every class in the package. I'm thinking that a happy medium might be to put a level of inclusion on your work, say if you use less than 50% of classes you should import them individually, but if you use more than 50% you should import the entire package.
I realise that it doesn't make a great deal of difference to the overall outcome of a project, I'm just looking for your opinions and experiences with it.

Answer 1

If you're working on a large codebase with a team, then it is helpful to use explicit imports, so that others can readily see which package particular classes come from.
Also consider the case where there two classes from different packages share a name. In this case you must use at least one explicit import.
But what if this situation doesn't exist (yet). You import two packages using wildcards. And then later someone comes along and creates a class in the second package with a name used by a class in the first package. Suddenly the class with the wildcard imports won't compile. Perhaps this is a contrived example.
Regarding personal practice, I usually use explicit imports for the first reason listed above. But secondly, I like to do so because it forces me to remember the package to which the class belongs. Most programmers type pretty quickly, so it's not much of a burden.
By the way, the compile-time cost, if it is even measurable, is no factor whatsoever. Writing readable and maintainable code is much more important.