There is no runtime penalty for using import package.* and import package.class in Java. The only different is in compile time, the import package.* will search for whole package to find the correct class' information.
The Single-Type-Import (e.g., import java.util.Vector) increases the readability of the program and it will be very clear which classes have been used.
The Type-Import-on-Demand (e.g. import java.util.*) causes the simple names of all public types declared in the package java.util to be available within the class and interface declarations of the compilation unit.