为什么在linux命令(iostat)中每秒钟读取(r/s)是零?

I run a java code that produces a lot of read and write from/to a text file. The program source is very simple and in a loop I write 2000 lines in a test file and then I read them again just to generate a lot of read and write to the disk. But when program is running I I run a java code that produces a lot of read a