avoid calling a heavy-cost method to log

Steps to Reproduce

1. import a 50MB file and profile with VisaulVM sampler

Current Result

SheetRegion.getReferenceString() takes some time which is unexpected

Expected Result

SheetRegion.getReferenceString() should not be invoked by logger when log level is higher than DEBUG

Debug Information

• parameterized messages only save the cost of calling toString(). the logger stills call a new statement or other methods before creating a logger message.
• should pass a variable instead of calling a method.