Here you can find the source of length(Iterator> iter)
public static int length(Iterator<?> iter)
//package com.java2s; /*//from ww w .j a v a 2 s. c o m * Copyright (C) 2016 Chan Chung Kwong <1m02math@126.com> * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <http://www.gnu.org/licenses/>. */ import java.util.*; public class Main { public static int length(Iterator<?> iter) { int len = 0; while (iter.hasNext()) { iter.next(); ++len; } return len; } }