001 /*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package com.google.common.collect;
018
019 import com.google.common.annotations.GwtCompatible;
020 import com.google.common.annotations.GwtIncompatible;
021
022 import java.util.Collection;
023
024 import javax.annotation.Nullable;
025
026 /**
027 * Static utility methods pertaining to object arrays.
028 *
029 * @author Kevin Bourrillion
030 * @since 2.0 (imported from Google Collections Library)
031 */
032 @GwtCompatible(emulated = true)
033 public final class ObjectArrays {
034 private ObjectArrays() {}
035
036 /**
037 * Returns a new array of the given length with the specified component type.
038 *
039 * @param type the component type
040 * @param length the length of the new array
041 */
042 @GwtIncompatible("Array.newInstance(Class, int)")
043 public static <T> T[] newArray(Class<T> type, int length) {
044 return Platform.newArray(type, length);
045 }
046
047 /**
048 * Returns a new array of the given length with the same type as a reference
049 * array.
050 *
051 * @param reference any array of the desired type
052 * @param length the length of the new array
053 */
054 public static <T> T[] newArray(T[] reference, int length) {
055 return Platform.newArray(reference, length);
056 }
057
058 /**
059 * Returns a new array that contains the concatenated contents of two arrays.
060 *
061 * @param first the first array of elements to concatenate
062 * @param second the second array of elements to concatenate
063 * @param type the component type of the returned array
064 */
065 @GwtIncompatible("Array.newInstance(Class, int)")
066 public static <T> T[] concat(T[] first, T[] second, Class<T> type) {
067 T[] result = newArray(type, first.length + second.length);
068 System.arraycopy(first, 0, result, 0, first.length);
069 System.arraycopy(second, 0, result, first.length, second.length);
070 return result;
071 }
072
073 /**
074 * Returns a new array that prepends {@code element} to {@code array}.
075 *
076 * @param element the element to prepend to the front of {@code array}
077 * @param array the array of elements to append
078 * @return an array whose size is one larger than {@code array}, with
079 * {@code element} occupying the first position, and the
080 * elements of {@code array} occupying the remaining elements.
081 */
082 public static <T> T[] concat(@Nullable T element, T[] array) {
083 T[] result = newArray(array, array.length + 1);
084 result[0] = element;
085 System.arraycopy(array, 0, result, 1, array.length);
086 return result;
087 }
088
089 /**
090 * Returns a new array that appends {@code element} to {@code array}.
091 *
092 * @param array the array of elements to prepend
093 * @param element the element to append to the end
094 * @return an array whose size is one larger than {@code array}, with
095 * the same contents as {@code array}, plus {@code element} occupying the
096 * last position.
097 */
098 public static <T> T[] concat(T[] array, @Nullable T element) {
099 T[] result = arraysCopyOf(array, array.length + 1);
100 result[array.length] = element;
101 return result;
102 }
103
104 /** GWT safe version of Arrays.copyOf. */
105 static <T> T[] arraysCopyOf(T[] original, int newLength) {
106 T[] copy = newArray(original, newLength);
107 System.arraycopy(
108 original, 0, copy, 0, Math.min(original.length, newLength));
109 return copy;
110 }
111
112 /**
113 * Returns an array containing all of the elements in the specified
114 * collection; the runtime type of the returned array is that of the specified
115 * array. If the collection fits in the specified array, it is returned
116 * therein. Otherwise, a new array is allocated with the runtime type of the
117 * specified array and the size of the specified collection.
118 *
119 * <p>If the collection fits in the specified array with room to spare (i.e.,
120 * the array has more elements than the collection), the element in the array
121 * immediately following the end of the collection is set to {@code null}.
122 * This is useful in determining the length of the collection <i>only</i> if
123 * the caller knows that the collection does not contain any null elements.
124 *
125 * <p>This method returns the elements in the order they are returned by the
126 * collection's iterator.
127 *
128 * <p>TODO(kevinb): support concurrently modified collections?
129 *
130 * @param c the collection for which to return an array of elements
131 * @param array the array in which to place the collection elements
132 * @throws ArrayStoreException if the runtime type of the specified array is
133 * not a supertype of the runtime type of every element in the specified
134 * collection
135 */
136 static <T> T[] toArrayImpl(Collection<?> c, T[] array) {
137 int size = c.size();
138 if (array.length < size) {
139 array = newArray(array, size);
140 }
141 fillArray(c, array);
142 if (array.length > size) {
143 array[size] = null;
144 }
145 return array;
146 }
147
148 /**
149 * Returns an array containing all of the elements in the specified
150 * collection. This method returns the elements in the order they are returned
151 * by the collection's iterator. The returned array is "safe" in that no
152 * references to it are maintained by the collection. The caller is thus free
153 * to modify the returned array.
154 *
155 * <p>This method assumes that the collection size doesn't change while the
156 * method is running.
157 *
158 * <p>TODO(kevinb): support concurrently modified collections?
159 *
160 * @param c the collection for which to return an array of elements
161 */
162 static Object[] toArrayImpl(Collection<?> c) {
163 return fillArray(c, new Object[c.size()]);
164 }
165
166 private static Object[] fillArray(Iterable<?> elements, Object[] array) {
167 int i = 0;
168 for (Object element : elements) {
169 array[i++] = element;
170 }
171 return array;
172 }
173
174 /**
175 * Swaps {@code array[i]} with {@code array[j]}.
176 */
177 static void swap(Object[] array, int i, int j) {
178 Object temp = array[i];
179 array[i] = array[j];
180 array[j] = temp;
181 }
182 }