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数组 [2,2,3,4,9,3] 给一个元素 6 找出数组中两个元素之和等于它，并返回数组坐标。思路：使用map，key用来记录arr[i]的值，value用来记录对应的下标，使用 containsKey 或者 get 进行逻辑判断 arr[?] = target - arr[??]

@BenchmarkMode(Mode.Throughput)
@Warmup(iterations = 3)
@Measurement(iterations = 10, time = 5, timeUnit = TimeUnit.SECONDS)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
public class TestFindArrayIndex {

    @Benchmark
    public  int[] findIndexOfArray1() {
        int[] arr = new int[] {2,2,3,4,9,3}; int target = 6;
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < arr.length; i++) {
            if (map.containsKey(target - arr[i])) {
                return new int[] {map.get(target - arr[i]),i};
            }
            map.put(arr[i], i);
        }
        return null;
    }

    @Benchmark
    public  int[] findIndexOfArray2() {
        int[] arr = new int[] {2,2,3,4,9,3}; int target = 6;
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < arr.length; i++) {
            if (map.get(arr[i]) != null) {
                return new int[]{map.get(arr[i]), i};
            }
            map.put(target - arr[i], i);
        }
        return null;
    }

    public static void main(String[] args) throws RunnerException {
        Options opt = new OptionsBuilder()
                .include(TestFindArrayIndex.class.getSimpleName())
                .output("Benchmark.log")
                .forks(1)
                .build();
        new Runner(opt).run();
    }
}

给出了两个性能差不多的方案，使用 JMH 性能测试，更多例子参考 ，影响基准测试的因素比较多，包括代码预热、编译器动态优化、资源回收（GC）、文件缓存、电源、其他程序，JVM的VM选项等等，详细参考

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源码

Thus “FooBah” becomes “fooBah” and “X” becomes “x”, but “URL” stays as “URL”.
如果一个类名是以两个大写字母开头的，则首字母不变，其它情况下默认首字母变成小写。

/**
 * Utility method to take a string and convert it to normal Java variable
 * name capitalization.  This normally means converting the first
 * character from upper case to lower case, but in the (unusual) special
 * case when there is more than one character and both the first and
 * second characters are upper case, we leave it alone.
 * <p>
 * Thus "FooBah" becomes "fooBah" and "X" becomes "x", but "URL" stays
 * as "URL".
 *
 * @param  name The string to be decapitalized.
 * @return  The decapitalized version of the string.
 */
public static String decapitalize(String name) {
    if (name == null || name.length() == 0) {
        return name;
    }
    if (name.length() > 1 && Character.isUpperCase(name.charAt(1)) &&
                    Character.isUpperCase(name.charAt(0))){
        return name;
    }
    char chars[] = name.toCharArray();
    chars[0] = Character.toLowerCase(chars[0]);
    return new String(chars);
}

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执行步骤

查看 docker search vsftpd

NAME                                     DESCRIPTION                                     STARS               OFFICIAL            AUTOMATED
fauria/vsftpd                            vsftpd Docker image based on Centos 7. Suppo…   153                                     [OK]
panubo/vsftpd                            vsftpd - Secure, fast FTP server                36                                      [OK]
vimagick/vsftpd                                                                          13                                      [OK]
odiobill/vsftpd                          Very light vsftpd installation based on Debi…   7                                       [OK]
million12/vsftpd                         VSFTPD Server in a Docker                       7                                       [OK]
emilybache/vsftpd-server                                                                 6                                       [OK]
avenus/vsftpd-alpine                     Docker image of vsftpd server based on Alpin…   5                                       [OK]
wildscamp/vsftpd                         An FTP server designed to simplify local dev…   4                                       [OK]
loicmathieu/vsftpd                       vsftpd container                                2                                       [OK]
akue/vsftpd                              vsftpd Docker image based on Centos 7. Suppo…   1
hiproz/vsftpd                            an vsftpd that support virtual user which ha…   1
benssson/vsftpd                          copy of wildscamp/vsftpd but with pasv_addr_…   1                                       [OK]
instantlinux/vsftpd                      A clean, easy-to-use, tiny yet full-featured…   1                                       [OK]
mikenye/vsftpd-anon-uploads              A generic, ready-to-go anonymous ftp server …   1                                       [OK]
undying/vsftpd                           Vsftpd Docker Container                         0                                       [OK]
ledermann/vsftpd                         Clone of helderco/docker-vsftpd, just to pro…   0
dmanas/vsftpd-mysql                                                                      0
dolphyvn/vsftpd_priv                                                                     0
markhobson/vsftpd                                                                        0
valus/vsftpd                             vsftpd on CentOS 7 for internal usage.          0
shourai/vsftpd-alpine                    vsftpd based on alpine                          0
ernestas/vsftpd-server                   simple vsftpd server                            0                                       [OK]
openmicroscopy/vsftpd-anonymous-upload   Vsftpd Docker image for anonymous FTP upload…   0                                       [OK]
zloystrelok/vsftpd                       fixed fork vsftpd                               0
vistrcm/vsftpd                           This Docker container implements a vsftpd se…   0                                       [OK]

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