为什么我们已经有StringBuilder的StringJoiner？ [英] Why StringJoiner when we already have StringBuilder?

问题描述

我最近遇到过Java 8类 StringJoiner 使用分隔符添加String并添加前缀和后缀，但我无法理解这个类的需要，因为它也使用 StringBuilder 在后端并且还执行非常简单的附加字符串的操作。

I recently encountered with a Java 8 class StringJoiner which adds the String using the delimiters and adds prefix and suffix to it, but I can't understand the need of this class as it also uses StringBuilder at the backend and also performs very simple operation of appending the Strings.

我是否因为没有真正理解这个类的真正目的而错过了什么？

Am I missing something by not actually understanding the real purpose of this class?

推荐答案

StringJoiner 非常有用，当你需要以<$ c $加入字符串时c> Stream 。

StringJoiner is very useful, when you need to join Strings in a Stream.

例如，如果你必须遵循字符串列表：

As an example, if you have to following List of Strings:

final List<String> strings = Arrays.asList("Foo", "Bar", "Baz");

使用起来要简单得多

final String collectJoin = strings.stream().collect(Collectors.joining(", "));

与 StringBuilder 一样：

final String collectBuilder =
    strings.stream().collect(Collector.of(StringBuilder::new,
        (stringBuilder, str) -> stringBuilder.append(str).append(", "),
        StringBuilder::append,
        StringBuilder::toString));

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