哪一个在性能方面更好？
finalWords.stream().forEach(word -> stringBuilder.append(word).append(”,“));
String finalResult = stringBuilder.toString();
VS
String finalResult = finalWords.stream().collect(Collectors.joining(","));
答案 0 :(得分：4)
我整理了一个小基准测试，因为我很好奇。它使用List随机生成的小写size初始化String，每个10的长度为@State(Scope.Benchmark)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Warmup(iterations = 5, time = 500, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
@Fork(3)
public class MyBenchmark {
@Param({"10", "100", "1000", "10000", "100000"})
private int size;
private List<String> finalWords;
@Setup(Level.Invocation)
public void initialize() {
finalWords = IntStream.range(0, size)
.mapToObj(i -> {
return ThreadLocalRandom.current()
.ints(10, 'a', 'z' + 1)
.mapToObj(c -> Character.toString((char) c))
.collect(Collectors.joining());
}).collect(Collectors.toList());
}
public static void main(String[] args) throws Exception {
org.openjdk.jmh.Main.main(args);
}
@Benchmark
public String stringBuilder() {
StringBuilder sb = new StringBuilder();
finalWords.forEach(word -> sb.append(word).append(","));
return sb.toString();
}
@Benchmark
public String stream() {
return finalWords.stream().collect(Collectors.joining(","));
}
}
：
Benchmark (size) Mode Cnt Score Error Units
MyBenchmark.stream 10 avgt 30 242.330 ± 5.177 ns/op
MyBenchmark.stream 100 avgt 30 1426.333 ± 20.183 ns/op
MyBenchmark.stream 1000 avgt 30 30779.509 ± 1114.992 ns/op
MyBenchmark.stream 10000 avgt 30 720944.424 ± 27845.997 ns/op
MyBenchmark.stream 100000 avgt 30 7701294.456 ± 648084.759 ns/op
MyBenchmark.stringBuilder 10 avgt 30 170.566 ± 1.833 ns/op
MyBenchmark.stringBuilder 100 avgt 30 1166.153 ± 21.162 ns/op
MyBenchmark.stringBuilder 1000 avgt 30 32374.567 ± 979.288 ns/op
MyBenchmark.stringBuilder 10000 avgt 30 473022.229 ± 8982.260 ns/op
MyBenchmark.stringBuilder 100000 avgt 30 4524267.849 ± 242801.008 ns/op
结果如下：
StringBuilder如您所见，{"inputFile": [["Column1", "Column2", "Column3", "Column4", "Column5", "Column6", "Column7", "Column8", "Column9", "Column10"], ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J"], ["K", "L", "M", "N", "O", "P", "Q", "R", "S", "T"]]}
方法在这种情况下更快，即使我没有指定初始容量。