XSSFWorkbook uses much more memory than HSSFWorkbook?

[Bruce Jin]

My Excel file has 60,000 rows.
When I save it as filename.xls my Java can read it using HSSFWorkbook.
But if I save it as filename.xlsx and use XSSFWorkbook my Java program runs out of memory big time.

Use HSSFWorkbook it uses 300Mb memory.
Use XSSFWorkbook it runs out of memory at 1200Mb (the max allowed on my PC JVM).

Does XSSFWorkbook really use that much memory than HSSFWorkbook?

Thanks!

[Martijn Verburg]

I'm not a POI user, but instinctively it makes a horrible kind of sense. The XML format used in the later case would undoubtedly be incredibly verbose. However 1200Mb still seems a little excessive :-).