Java reduce sample

java_reduce.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

public class Main3 {

    public static void main(String[] args) {
        log(test01("abc"));
        log(test02("abc"));
        log(test03("snakeToCamel"));
        log(test04("snake_to_camel"));

        // test00();
        int r = Stream.of(1,2,3).reduce(10, (x,y) -> x + y);
        System.out.println(r); // 16

    }

    private static void log(Object obj) {
        System.out.println(obj);
    }

    private static String test04(String str) {
        return Arrays.stream(str.split("_"))
            .map(x -> x.substring(0,1).toUpperCase() + x.substring(1).toLowerCase())
            .collect(Collectors.joining());
    }

    private static String test03(String in) {
        String out = in.codePoints()
            .mapToObj(c -> (char)c) // IntStream to Stream<Character>
            .reduce("" ,
                (acc, v) -> acc + (Character.isLowerCase(v) ? v : "_" + Character.toLowerCase(v)) ,
                (s1, s2) -> s1 + s2
            );
        return out;
    }

    private static List<Character> test02(String in) {
        List<Character> out = in.codePoints()
            .mapToObj(c -> Character.valueOf((char)c))
            .reduce(new ArrayList() ,
                (acc, v) -> {acc.add(v);return acc;},
                (s1, s2) -> {s1.addAll(s2);return s1;}
            );
        return out;
    }

    private static String test01(String in) {
        String out = in.codePoints()
            .mapToObj(x -> String.valueOf(x))
            .reduce("x" ,
                (String acc, String v) -> acc + "_" + v,
                (String s1, String s2) -> s1 + s2
            );
        return out;
    }


     private static String test00() {
        List<String> tokens = new ArrayList<String>();
        for (int i = 0; i < 1000; i++) {
            tokens.add("_" + i + "\n");
        }
        String ret = tokens.parallelStream().reduce("", String::concat, String::concat);
        return ret;
    }



}