- Base of all "Object" for equals() and
toString() methods.
- Exception class. You can't do away
with it.
- Collections API. Almost everything
from Collections API is useful and
used in your code.
- System class for System.out.println.
But it is almost replaced by logger
API.
- ThreadPoolExecutor if your product
really uses threads and you really
care about them being controlled :).
- JDBC API. Solely based on if we are
talking about usage. But even this is
going in background due to use of
Hibernate (ORM tools)
Tried to list few useful ones, But I think list will really go long.
