Here you can find the source of joinToString(List> list)
public static String joinToString(List<?> list)
//package com.java2s; import java.util.List; public class Main { public static String joinToString(List<?> list) { StringBuffer strBuf = new StringBuffer(); if (list != null) { for (Object item : list) { strBuf.append(item.toString()); }/*from w w w .j av a 2s. c o m*/ } return strBuf.toString(); } }