Hi there, so we learned the string, StringBuilder, and the StringBuffer classes. So, what's the difference between these classes? Now, let's look at the difference between string, StringBuffer, and StringBuilder. The string object is stored in string pool but StringBuffer and StringBuilder objects are stored in heap. The string object is immutable in Java but StringBuffer and StringBuilder are mutable objects. This is the main difference and it is very important. The performance of string and StringBuilder is fast, but StringBuffer is slow because StringBuffer is a synchronized class. StringBuilder and StringBuffer are almost the same. The main difference is that StringBuffer is synchronized and StringBuilder is not synchronized. 

So, StringBuilder is faster than StringBuffer, but the performance difference is negligible for small programs, their functionality is the same. If your program is used by multiple threads, then it's better to use StringBuffer. If your program is used by a single thread then use StringBuilder. Yes, those are the main differences between these classes. The most important thing for you and you should pay attention to is that the StringBuilder and StringBuffer classes are mutable, while the string class is immutable. Because of this difference, comparing the equations of objects with each other produces different results. We have explained this in our previous lessons. Let's take a short break now. See you in the next lesson.