Java 获取字符在字符串中出现位置下标索引的方法

1､ 使用IntStream实现的几种方法

intStream文档：https://docs.oracle.com/javase/8/docs/api/java/util/stream/IntStream.html

1) IntStream.range

public static List getIndexList(String s, char c) {
    return IntStream.range(0, s.length())
                    .filter(index -> s.charAt(index) == c)
                    .boxed()
                    .collect(Collectors.toList());
}

2) IntStream.iterate

public static List getIndexList(String s, char c) {    return IntStream.iterate(s.indexOf(c), i -> s.indexOf(c, i + 1))            .takeWhile(i -> i > -1)            .boxed()            .collect(Collectors.toList());}

或

private static List getIndexList(String word, char c) {  return IntStream          .iterate(word.indexOf(c), index -> index >= 0, index -> word.indexOf(c, index + 1))          .boxed()          .collect(Collectors.toList());}

2､使用Stream.of实现

Stream.of("Hello world!")            .map(Scanner::new)            .flatMap(s -> s.findAll("l"))            .map(mr -> mr.start())            .forEach(System.out::println);