GenericsUtil.java
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上传日期:2018-01-08
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文件大小:2k
- /**
- * 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.
- */
- package org.apache.hadoop.util;
- import java.lang.reflect.Array;
- import java.util.List;
- /**
- * Contains utility methods for dealing with Java Generics.
- */
- public class GenericsUtil {
- /**
- * Returns the Class object (of type <code>Class<T></code>) of the
- * argument of type <code>T</code>.
- * @param <T> The type of the argument
- * @param t the object to get it class
- * @return <code>Class<T></code>
- */
- public static <T> Class<T> getClass(T t) {
- @SuppressWarnings("unchecked")
- Class<T> clazz = (Class<T>)t.getClass();
- return clazz;
- }
- /**
- * Converts the given <code>List<T></code> to a an array of
- * <code>T[]</code>.
- * @param c the Class object of the items in the list
- * @param list the list to convert
- */
- public static <T> T[] toArray(Class<T> c, List<T> list)
- {
- @SuppressWarnings("unchecked")
- T[] ta= (T[])Array.newInstance(c, list.size());
- for (int i= 0; i<list.size(); i++)
- ta[i]= list.get(i);
- return ta;
- }
- /**
- * Converts the given <code>List<T></code> to a an array of
- * <code>T[]</code>.
- * @param list the list to convert
- * @throws ArrayIndexOutOfBoundsException if the list is empty.
- * Use {@link #toArray(Class, List)} if the list may be empty.
- */
- public static <T> T[] toArray(List<T> list) {
- return toArray(getClass(list.get(0)), list);
- }
- }