Hello ChenJY,
Can you clarify what kind of Java class you are creating? For example, are you trying to create a Java class that extends one of DevTest's SDK base classes, such as a custom Data Protocol Handler for a virtual service or a custom Test step for Application Test?
If this is the case, and you are trying to import the Logger class to log or output debug to a log file, then you'll need to import the following class and package and typically declare your Logger like the following:
import org.apache.log4j.Logger;
public class MyCustomDPH extends DataProtocol {
private static final Logger log = Logger.getLogger(MyCustomDPH.class);
....
}