String concatenation in a for loop. Java 9

Question

Please correct me if i\'m wrong. In Java 8, for performance reasons, when concatenating several strings by the \"+\" operator StringBuffer was invoked. And the problem of cr

Answer 1

For the record, here is a JMH test...

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
@Warmup(iterations = 5, time = 5, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 5, time = 5, timeUnit = TimeUnit.SECONDS)
@State(Scope.Thread)
public class LoopTest {

    public static void main(String[] args) throws RunnerException {
        Options opt = new OptionsBuilder().include(LoopTest.class.getSimpleName())
                .jvmArgs("-ea", "-Xms10000m", "-Xmx10000m")
                .shouldFailOnError(true)
                .build();
        new Runner(opt).run();
    }

    @Param(value = {"1000", "10000", "100000"})
    int howmany;

    @Fork(1)
    @Benchmark
    public String concatBuilder(){
        StringBuilder sb = new StringBuilder();
        for(int i=0;i

Produces result (only for 100000 shown here) that I did not really expect:

LoopTest.concatPlain       100000  avgt    5  3902.711 ± 67.215  ms/op
LoopTest.concatBuilder     100000  avgt    5     1.850 ±  0.574  ms/op