Here you can find the source of toIntArray(Collection
public static int[] toIntArray(Collection<Integer> collection)
//package com.java2s; /*/*from ww w . j a v a2 s . co m*/ * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ import java.util.Collection; import java.util.Iterator; import java.util.List; public class Main { public static int[] toIntArray(Collection<Integer> collection) { int[] newArray = new int[collection.size()]; if (collection instanceof List) { List<Integer> list = (List<Integer>) collection; for (int i = 0; i < list.size(); i++) { Integer value = list.get(i); newArray[i] = value.intValue(); } } else { int i = 0; Iterator<Integer> iterator = collection.iterator(); while (iterator.hasNext()) { Integer value = iterator.next(); newArray[i++] = value.intValue(); } } return newArray; } }