Here you can find the source of first(Iterable
| Parameter | Description |
|---|---|
| T | the element type |
| iterable | the collection |
public static <T> T first(Iterable<T> iterable)
//package com.java2s; /*//w w w. j a v a 2 s. com * DuDe - The Duplicate Detection Toolkit * * Copyright (C) 2010 Hasso-Plattner-Institut f?r Softwaresystemtechnik GmbH, * Potsdam, Germany * * This file is part of DuDe. * * DuDe 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. * * DuDe 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 DuDe. If not, see <http://www.gnu.org/licenses/>. * */ import java.util.Deque; import java.util.Iterator; import java.util.List; public class Main { /** * Returns the first element of the collection. * * @param <T> * the element type * @param list * the collection * @return the first element or null if the list is empty */ @SuppressWarnings("unchecked") public static <T> T first(List<T> list) { if (list instanceof Deque<?>) return ((Deque<T>) list).getFirst(); return list.isEmpty() ? null : list.get(0); } /** * Returns the first element of the collection. * * @param <T> * the element type * @param iterable * the collection * @return the first element or null if the list is empty */ public static <T> T first(Iterable<T> iterable) { if (iterable instanceof Deque<?>) return ((Deque<T>) iterable).getFirst(); if (iterable instanceof List<?>) { List<T> list = (List<T>) iterable; return list.isEmpty() ? null : list.get(0); } Iterator<T> iterator = iterable.iterator(); return iterator.hasNext() ? iterator.next() : null; } }