Here you can find the source of concat(String[] parts)
public static String concat(String[] parts)
//package com.java2s; //License from project: Open Source License import java.util.Arrays; public class Main { public static String concat(String[] parts) { return Arrays.stream(parts).reduce((a, b) -> a.concat(" ").concat(b)).orElse(""); }/* w ww . j a va 2 s. c o m*/ }