Zhiqiang Please don't cross post questions to multiple forums. You posted this exact same question in three different forums. Most of the people here at the Ranch visit multiple forums and will answer questions in more than one. Cross posting your message will actually reduce the chance of getting it answered becasu they will think it will get an answer in another forum. As it isn't really a beginner question I am closing this thread.
------------------ Dave Sun Certified Programmer for the Java� 2 Platform
I've got no option but to sell you all for scientific experiments. Or a tiny ad: