将for循环转换为concat String为lambda表达式 [英] Convert a for loop to concat String into a lambda expression

问题描述

我有以下for循环遍历字符串列表，并将每个单词的第一个字符存储在 StringBuilder 中。我想知道如何将其转换为lambda表达式

I have the following for loop which iterates through a list of strings and stores the first character of each word in a StringBuilder. I would like to know how can I transform this to a lambda expression

StringBuilder chars = new StringBuilder();
for (String l : list) {
    chars.append(l.charAt(0));
}  

推荐答案

假设你调用<$ c之后，我想你只是在寻找 toString（）上的 StringBuilder oracle.com/javase/8/docs/api/java/util/stream/Collectors.html#joining - > Collectors.joining（） ，在将每个字符串映射到单字符子串后：

Assuming you call toString() on the StringBuilder afterwards, I think you're just looking for Collectors.joining(), after mapping each string to a single-character substring:

String result = list
    .stream()
    .map(s -> s.substring(0, 1))
    .collect(Collectors.joining());

示例代码：

import java.util.*;
import java.util.stream.*;

public class Test {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("foo");
        list.add("bar");
        list.add("baz");
        String result = list
            .stream()
            .map(s -> s.substring(0, 1))
            .collect(Collectors.joining());
        System.out.println(result); // fbb
    }
}

注意使用 substring 而不是 charAt ，因此我们仍然有一串字符串。

Note the use of substring instead of charAt, so we still have a stream of strings to work with.

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