1 /** 2 * Licensed to the Apache Software Foundation (ASF) under one 3 * or more contributor license agreements. See the NOTICE file 4 * distributed with this work for additional information 5 * regarding copyright ownership. The ASF licenses this file 6 * to you under the Apache License, Version 2.0 (the 7 * "License"); you may not use this file except in compliance 8 * with the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 package org.apache.hadoop.util; 20 21 import java.lang.reflect.Array; 22 import java.util.List; 23 24 import org.apache.hadoop.classification.InterfaceAudience; 25 import org.apache.hadoop.classification.InterfaceStability; 26 27 /** 28 * Contains utility methods for dealing with Java Generics. 29 */ 30 @InterfaceAudience.Private 31 @InterfaceStability.Unstable 32 public class GenericsUtil { 33 34 /** 35 * Returns the Class object (of type <code>Class<T></code>) of the 36 * argument of type <code>T</code>. 37 * @param <T> The type of the argument 38 * @param t the object to get it class 39 * @return <code>Class<T></code> 40 */ getClass(T t)41 public static <T> Class<T> getClass(T t) { 42 @SuppressWarnings("unchecked") 43 Class<T> clazz = (Class<T>)t.getClass(); 44 return clazz; 45 } 46 47 /** 48 * Converts the given <code>List<T></code> to a an array of 49 * <code>T[]</code>. 50 * @param c the Class object of the items in the list 51 * @param list the list to convert 52 */ toArray(Class<T> c, List<T> list)53 public static <T> T[] toArray(Class<T> c, List<T> list) 54 { 55 @SuppressWarnings("unchecked") 56 T[] ta= (T[])Array.newInstance(c, list.size()); 57 58 for (int i= 0; i<list.size(); i++) 59 ta[i]= list.get(i); 60 return ta; 61 } 62 63 64 /** 65 * Converts the given <code>List<T></code> to a an array of 66 * <code>T[]</code>. 67 * @param list the list to convert 68 * @throws ArrayIndexOutOfBoundsException if the list is empty. 69 * Use {@link #toArray(Class, List)} if the list may be empty. 70 */ toArray(List<T> list)71 public static <T> T[] toArray(List<T> list) { 72 return toArray(getClass(list.get(0)), list); 73 } 74 75 } 76