Java – convert a for loop to a concat string of a lambda expression

I have the following for loop to traverse a string list and store the first character of each word in StringBuilder I want to know how to convert it to a lambda expression

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

Solution

Assuming you call toString () after StringBuilder, I think you are looking for Collectors. after mapping each string to a single character substring. joining()：

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

Example code:

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
    }
}

Note that substrings are used instead of charat, so we still have a string to deal with