LoopStringsBenchmark.java

package scratch;

import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.infra.Blackhole;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;

import java.util.UUID;
import java.util.concurrent.TimeUnit;

@Warmup(iterations = 10, time = 1, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 10, time = 1, timeUnit = TimeUnit.SECONDS)
@Fork(1)
@State(Scope.Thread)
public class LoopStringsBenchmark {

    public static void main(String[] args) throws RunnerException {
        Options opt = new OptionsBuilder()
                .include(LoopStringsBenchmark.class.getSimpleName())
                .forks(1)
                .build();

        new Runner(opt).run();
    }

    private String[] strings;

    @Setup
    public void setupTest() {
        strings = new String[100];
        for (int i = 0; i < 100; i++) {
            strings[i] = UUID.randomUUID().toString().substring(0, 10);
        }
    }

    @Benchmark
    public void testPlus(Blackhole bh) {
        String combined = "";
        for (String s : strings) {
            combined = combined + s;
        }
        bh.consume(combined);
    }

    @Benchmark
    public void testStringBuilder(Blackhole bh) {
        StringBuilder sb = new StringBuilder();
        for (String s : strings) {
            sb.append(s);
        }
        bh.consume(sb.toString());
    }

    @Benchmark
    public void testStringBuffer(Blackhole bh) {
        StringBuffer sb = new StringBuffer();
        for (String s : strings) {
            sb.append(s);
        }
        bh.consume(sb.toString());
    }

    @Benchmark
    public void testStringJoiner(Blackhole bh) {
        bh.consume(String.join("", strings));
    }

    @Benchmark
    public void testStringConcat(Blackhole bh) {
        String combined = "";
        for (String s : strings) {
            combined.concat(s);
        }
        bh.consume(combined);
    }
}

// Java 8 results
//# Run complete. Total time: 00:00:51
//
//        Benchmark                                Mode  Cnt       Score        Error  Units
//        LoopStringsBenchmark.testPlus           thrpt   10   80120.589 ±  18155.538  ops/s
//        LoopStringsBenchmark.testStringBuffer   thrpt   10  595825.572 ± 233297.303  ops/s
//        LoopStringsBenchmark.testStringBuilder  thrpt   10  596329.000 ± 270195.655  ops/s
//        LoopStringsBenchmark.testStringConcat   thrpt   10  428817.984 ±  96583.918  ops/s
//        LoopStringsBenchmark.testStringJoiner   thrpt   10  449707.702 ±  79852.503  ops/s
//
//
// Java 7 results
//        Benchmark                                Mode  Cnt       Score       Error  Units
//        LoopStringsBenchmark.testPlus           thrpt   10   82123.780 ±  5162.099  ops/s
//        LoopStringsBenchmark.testStringBuffer   thrpt   10  526157.298 ± 67294.995  ops/s
//        LoopStringsBenchmark.testStringBuilder  thrpt   10  579148.486 ± 77417.358  ops/s
//        LoopStringsBenchmark.testStringConcat   thrpt   10  479200.469 ± 57042.272  ops/s