当我们已经有了 StringBuilder 时，为什么要使用 StringJoiner? [英] Why StringJoiner when we already have StringBuilder?

问题描述

我最近遇到了一个 Java 8 类 StringJoiner 它使用分隔符添加字符串并为其添加前缀和后缀，但我无法理解此类的需要，因为它也使用 StringBuilder 在后端，也执行非常简单的追加操作字符串.

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门课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，当你需要在 Stream 中加入 Strings 时.

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

例如，如果您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");

使用起来更简单

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

就像使用 StringBuilder 一样:

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

6 年后编辑正如评论中所指出的，现在有更简单的解决方案，例如 String.join(", ", strings)，当时还没有这些解决方案.但是用例还是一样的.

EDIT 6 years later As noted in the comments, there are now much simpler solutions like String.join(", ", strings), which were not available back then. But the use case is still the same.

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