程序员的小窝

What is the main difference between StringBuffer and StringBuilder? Is there any performance issues when deciding on any one of these?

StringBuffer is synchronized, StringBuilder is not.

StringBuilder is faster than StringBuffer because it's not synchronized.

Here's a simple benchmark test:

public class Main {
    public static void main(String[] args) {
        int N = 77777777;
        long t;

        {
            StringBuffer sb = new StringBuffer();
            t = System.currentTimeMillis();
            for (int i = N; i --> 0 ;) {
                sb.append("");
            }
            System.out.println(System.currentTimeMillis() - t);
        }

        {
            StringBuilder sb = new StringBuilder();
            t = System.currentTimeMillis();
            for (int i = N; i > 0 ; i--) {
                sb.append("");
            }
            System.out.println(System.currentTimeMillis() - t);
        }
    }
}

A test run gives the numbers of 2241 ms for StringBuffer vs 753 ms for StringBuilder.