I know that the package
A good reason not to autoimport too much is to avoid namespace clashes. If everything in
java.util was imported automatically and then you wanted to refer to a different class named 'Map', for example, you would have to refer to it by its fully-qualified name.
In response to other answers in this thread,
import does not actually modify the internal representation of your class files. In fact, here is a link to the JVM spec describing the class file structure: see that imports are not stored anywhere.