This is the fifth article in the series of "Become a Java GC Expert". The author, a senior software engineer at NHN, explains about the principles of Java application performance tuning. Specifically, he explains what is required in order to tune the performance of Java application, the steps you need to perform to identify whether your application needs tuning. The author also explains the problems you may encounter during performance tuning. The article is finalized with the recommendations you need to follow to make better decisions when tuning Java applications.