Widely used classes, such as those in java.io and java.util, are well known to the typical Java programmer. When importing such classes, it's reasonable to use an abbreviated style:
When importing classes that are not among the most widely used, one should probably use another style, in which each class has an explicit import statement. If a class is unfamiliar to a reader, an explicit import makes it easier to find related documentation.
For example, if a class imports items from the Apache Commons FileUpload tool, then instead of :
import org.apache.commons.fileupload.*;one should likely use the more explicit style :
import org.apache.commons.fileupload.FileUploadException; import org.apache.commons.fileupload.FileItem; ...etc...