String Concatenation vs. StringBuffer

Main.java

public class Main {
    private static final int ITERATIONS = 100000;

    public static void main(String[] args) {
        long stringConcatTime = time(Main::stringConcat);
        System.out.println("String concat time: " + stringConcatTime + " ms");

        long stringBufferAppendTime = time(Main::stringBufferAppend);
        System.out.println("StringBuffer append time: " + stringBufferAppendTime + " ms");
    }

    private static void stringConcat() {
        String s = "";
        for (int i=0; i<ITERATIONS; i++) {
            s += 'a';
        }
        System.out.println(s.length());
    }

    private static void stringBufferAppend() {
        StringBuffer sb = new StringBuffer();
        for (int i=0; i<ITERATIONS; i++) {
            sb.append('a');
        }
        String s = sb.toString();
        System.out.println(s.length());
    }

    private static long time(Runnable runnable) {
        long start = System.currentTimeMillis();
        runnable.run();
        long finish = System.currentTimeMillis();
        long delta = finish-start;
        return delta;
    }
}

Output with Oracle JDK8:

100000
String concat time: 4527 ms
100000
StringBuffer append time: 3 ms