StringJoinBench.java

package si.pele.jmh;

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.Param;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Warmup;

import java.util.SplittableRandom;
import java.util.StringJoiner;
import java.util.concurrent.TimeUnit;

@BenchmarkMode(Mode.Throughput)
@Warmup(iterations = 5, time = 500, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
@State(Scope.Benchmark)
@Fork(1)
public class StringJoinBench {
    static final String utf16chars = "ČŠŽĐĆ";

    @Param("10")
    int numElem;

    @Param({"10", "20", "100", "1000"})
    int elemLength;

    @Param({"LATIN1", "UTF16"})
    Coder coder;

    public enum Coder {
        LATIN1, UTF16
    }

    private String[] elements;

    @Setup
    public void setup() {
        var rnd = new SplittableRandom(0L); // deterministic
        elements = new String[numElem];
        for (int i = 0; i < numElem; i++) {
            StringBuilder sb = new StringBuilder(elemLength);
            for (int j = 0; j < elemLength; j++) {
                char l1char = (char) rnd.nextInt(' ', '~');
                char utf16char = utf16chars.charAt(rnd.nextInt(utf16chars.length()));
                sb.append(coder == Coder.UTF16 &&
                          (j + 1 == elemLength || rnd.nextInt(10) == 0)
                          ? utf16char
                          : l1char);
            }
            elements[i] = sb.toString();
        }
    }

    @Benchmark
    public String join() {
        return String.join(",", elements);
    }

    @Benchmark
    public String stringJoiner() {
        var sj = new StringJoiner(",", "[", "]");
        for (var s : elements) {
            sj.add(s);
        }
        return sj.toString();
    }
}