有人能解释一下cpu stat中的美好时光吗？

I know the difference between user time and sys time. However, I'm not quite sure about the nice time. I used to know that nice time is the time used in nice pr, but when I did an experiment, I found that the nice time didn't grow up after I reniced a 100%-CPU-using program(infinite loop doing add in Java) to 19. So, I'm confused...I know the difference between user time and sys