将Iterable <Character>转换为String的最佳方法是什么？

Question

什么是一个转换的最简单的/最快的方式Iterable<Character>为String从可迭代的人物？

例如,如何将"A","B"和"C"的Iterable转换为字符串"ABC"？

所述iter.toString()返回字符串"[A,B,C]" .

Answer 1

5个版本:

1)通过StringBuilder.append()以下方式收集Java 8流:

public static String streamAppend(Iterable<Character> chars){
    return StreamSupport.stream(chars.spliterator(), true)
                        .collect(
                            StringBuilder::new,
                            StringBuilder::append,
                            StringBuilder::append
                         )
                        .toString();
}

Java 8 Streams收集通过 Collectors.joining()

public static String streamJoin(Iterable<Character> chars){
    return StreamSupport.stream(chars.spliterator(), true)
                        .map(Object::toString)
                        .collect(Collectors.joining(""));
}

使用Java 5 for循环的Pre-Java8-Version:

public static String java7(Iterable<Character> chars) {
    StringBuilder sb = new StringBuilder();
    for (Character c: chars) {
        sb.append(c);
    }
    return sb.toString();
}

番石榴版使用Joiner:

public static String guavaJoin(Iterable<Character> chars) {
    return Joiner.on("").join(chars);
}

使用Java 8版本Iterable.forEach()和方法引用:

public static String iterableForEach(Iterable<Character> chars){
    StringBuilder sb = new StringBuilder();
    chars.forEach(sb::append);
    return sb.toString();
}

在关于性能的讨论之后,我运行了一个JMH微基准测试来亲眼看看.结果很明显,但比预期的要严重得多.

Benchmark                           (mode)  (size)          Score    Units
CharsToString.stringJoin     STREAM_APPEND       1    5071451.223 ±  ops/s
CharsToString.stringJoin     STREAM_APPEND       2     481656.870 ±  ops/s
CharsToString.stringJoin     STREAM_APPEND       5     162359.508 ±  ops/s
CharsToString.stringJoin     STREAM_APPEND      10      76910.668 ±  ops/s
CharsToString.stringJoin     STREAM_APPEND      20      49590.249 ±  ops/s
CharsToString.stringJoin     STREAM_APPEND      50      44608.948 ±  ops/s
CharsToString.stringJoin     STREAM_APPEND     100      20940.993 ±  ops/s
CharsToString.stringJoin     STREAM_APPEND     200      29634.118 ±  ops/s
CharsToString.stringJoin     STREAM_APPEND     500      19387.956 ±  ops/s
CharsToString.stringJoin     STREAM_APPEND    1000      17629.508 ±  ops/s
CharsToString.stringJoin       STREAM_JOIN       1    3342341.147 ±  ops/s
CharsToString.stringJoin       STREAM_JOIN       2     279516.584 ±  ops/s
CharsToString.stringJoin       STREAM_JOIN       5     102312.667 ±  ops/s
CharsToString.stringJoin       STREAM_JOIN      10      61759.122 ±  ops/s
CharsToString.stringJoin       STREAM_JOIN      20      34802.386 ±  ops/s
CharsToString.stringJoin       STREAM_JOIN      50      37629.593 ±  ops/s
CharsToString.stringJoin       STREAM_JOIN     100      33493.715 ±  ops/s
CharsToString.stringJoin       STREAM_JOIN     200      26186.986 ±  ops/s
CharsToString.stringJoin       STREAM_JOIN     500      19264.628 ±  ops/s
CharsToString.stringJoin       STREAM_JOIN    1000      14446.396 ±  ops/s
CharsToString.stringJoin        GUAVA_JOIN       1    6570784.907 ±  ops/s
CharsToString.stringJoin        GUAVA_JOIN       2    3821031.465 ±  ops/s
CharsToString.stringJoin        GUAVA_JOIN       5    1574828.190 ±  ops/s
CharsToString.stringJoin        GUAVA_JOIN      10     806057.685 ±  ops/s
CharsToString.stringJoin        GUAVA_JOIN      20     356533.358 ±  ops/s
CharsToString.stringJoin        GUAVA_JOIN      50     156129.534 ±  ops/s
CharsToString.stringJoin        GUAVA_JOIN     100     100195.171 ±  ops/s
CharsToString.stringJoin        GUAVA_JOIN     200      54820.347 ±  ops/s
CharsToString.stringJoin        GUAVA_JOIN     500      20577.137 ±  ops/s
CharsToString.stringJoin        GUAVA_JOIN    1000      11465.704 ±  ops/s
CharsToString.stringJoin  ITERABLE_FOREACH       1   11921819.833 ±  ops/s
CharsToString.stringJoin  ITERABLE_FOREACH       2    7007911.144 ±  ops/s
CharsToString.stringJoin  ITERABLE_FOREACH       5    4415785.561 ±  ops/s
CharsToString.stringJoin  ITERABLE_FOREACH      10    2107685.852 ±  ops/s
CharsToString.stringJoin  ITERABLE_FOREACH      20    1158806.591 ±  ops/s
CharsToString.stringJoin  ITERABLE_FOREACH      50     482412.510 ±  ops/s
CharsToString.stringJoin  ITERABLE_FOREACH     100     265362.511 ±  ops/s
CharsToString.stringJoin  ITERABLE_FOREACH     200     123663.470 ±  ops/s
CharsToString.stringJoin  ITERABLE_FOREACH     500      49238.673 ±  ops/s
CharsToString.stringJoin  ITERABLE_FOREACH    1000      24328.723 ±  ops/s
CharsToString.stringJoin             JAVA7       1    9746936.478 ±  ops/s
CharsToString.stringJoin             JAVA7       2    6431473.785 ±  ops/s
CharsToString.stringJoin             JAVA7       5    2736936.112 ±  ops/s
CharsToString.stringJoin             JAVA7      10    1764353.273 ±  ops/s
CharsToString.stringJoin             JAVA7      20     833322.493 ±  ops/s
CharsToString.stringJoin             JAVA7      50     278354.933 ±  ops/s
CharsToString.stringJoin             JAVA7     100     180763.740 ±  ops/s
CharsToString.stringJoin             JAVA7     200      86729.675 ±  ops/s
CharsToString.stringJoin             JAVA7     500      38560.347 ±  ops/s
CharsToString.stringJoin             JAVA7    1000      17798.159 ±  ops/s

正如您所看到的,最后一个版本(iterableForEach)实际上是最快的版本,Java 7和Guava版本至少在类似的范围内.对于数百个元素下的大小,Streams失败,它们显然针对大型数据集进行了优化.但是在1000个元素中,它们表现得更好,几乎与Java 7版本相当.在大约10000个元素(不在此图表上),Streams优于其他解决方案.

基准代码作为GitHub要点提供,随时修改参数并检查机器上的结果.