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 017package com.google.common.collect; 018 019import static com.google.common.base.Preconditions.checkPositionIndexes; 020 021import com.google.common.annotations.GwtCompatible; 022import com.google.common.annotations.GwtIncompatible; 023import com.google.errorprone.annotations.CanIgnoreReturnValue; 024import java.lang.reflect.Array; 025import java.util.Arrays; 026import java.util.Collection; 027import org.checkerframework.checker.nullness.qual.NonNull; 028import org.checkerframework.checker.nullness.qual.Nullable; 029 030/** 031 * Static utility methods pertaining to object arrays. 032 * 033 * @author Kevin Bourrillion 034 * @since 2.0 035 */ 036@GwtCompatible(emulated = true) 037@ElementTypesAreNonnullByDefault 038@SuppressWarnings("AvoidObjectArrays") 039public final class ObjectArrays { 040 041 private ObjectArrays() {} 042 043 /** 044 * Returns a new array of the given length with the specified component type. 045 * 046 * @param type the component type 047 * @param length the length of the new array 048 */ 049 @GwtIncompatible // Array.newInstance(Class, int) 050 @SuppressWarnings("unchecked") 051 public static <T extends @Nullable Object> T[] newArray(Class<@NonNull T> type, int length) { 052 return (T[]) Array.newInstance(type, length); 053 } 054 055 /** 056 * Returns a new array of the given length with the same type as a reference array. 057 * 058 * @param reference any array of the desired type 059 * @param length the length of the new array 060 */ 061 public static <T extends @Nullable Object> T[] newArray(T[] reference, int length) { 062 return Platform.newArray(reference, length); 063 } 064 065 /** 066 * Returns a new array that contains the concatenated contents of two arrays. 067 * 068 * @param first the first array of elements to concatenate 069 * @param second the second array of elements to concatenate 070 * @param type the component type of the returned array 071 */ 072 @GwtIncompatible // Array.newInstance(Class, int) 073 public static <T extends @Nullable Object> T[] concat( 074 T[] first, T[] second, Class<@NonNull T> type) { 075 T[] result = newArray(type, first.length + second.length); 076 System.arraycopy(first, 0, result, 0, first.length); 077 System.arraycopy(second, 0, result, first.length, second.length); 078 return result; 079 } 080 081 /** 082 * Returns a new array that prepends {@code element} to {@code array}. 083 * 084 * @param element the element to prepend to the front of {@code array} 085 * @param array the array of elements to append 086 * @return an array whose size is one larger than {@code array}, with {@code element} occupying 087 * the first position, and the elements of {@code array} occupying the remaining elements. 088 */ 089 public static <T extends @Nullable Object> T[] concat(@ParametricNullness T element, T[] array) { 090 T[] result = newArray(array, array.length + 1); 091 result[0] = element; 092 System.arraycopy(array, 0, result, 1, array.length); 093 return result; 094 } 095 096 /** 097 * Returns a new array that appends {@code element} to {@code array}. 098 * 099 * @param array the array of elements to prepend 100 * @param element the element to append to the end 101 * @return an array whose size is one larger than {@code array}, with the same contents as {@code 102 * array}, plus {@code element} occupying the last position. 103 */ 104 public static <T extends @Nullable Object> T[] concat(T[] array, @ParametricNullness T element) { 105 T[] result = Arrays.copyOf(array, array.length + 1); 106 result[array.length] = element; 107 return result; 108 } 109 110 /** 111 * Returns an array containing all of the elements in the specified collection; the runtime type 112 * of the returned array is that of the specified array. If the collection fits in the specified 113 * array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the 114 * specified array and the size of the specified collection. 115 * 116 * <p>If the collection fits in the specified array with room to spare (i.e., the array has more 117 * elements than the collection), the element in the array immediately following the end of the 118 * collection is set to {@code null}. This is useful in determining the length of the collection 119 * <i>only</i> if the caller knows that the collection does not contain any null elements. 120 * 121 * <p>This method returns the elements in the order they are returned by the collection's 122 * iterator. 123 * 124 * <p>TODO(kevinb): support concurrently modified collections? 125 * 126 * @param c the collection for which to return an array of elements 127 * @param array the array in which to place the collection elements 128 * @throws ArrayStoreException if the runtime type of the specified array is not a supertype of 129 * the runtime type of every element in the specified collection 130 */ 131 static <T extends @Nullable Object> T[] toArrayImpl(Collection<?> c, T[] array) { 132 int size = c.size(); 133 if (array.length < size) { 134 array = newArray(array, size); 135 } 136 fillArray(c, array); 137 if (array.length > size) { 138 @Nullable Object[] unsoundlyCovariantArray = array; 139 unsoundlyCovariantArray[size] = null; 140 } 141 return array; 142 } 143 144 /** 145 * Implementation of {@link Collection#toArray(Object[])} for collections backed by an object 146 * array. the runtime type of the returned array is that of the specified array. If the collection 147 * fits in the specified array, it is returned therein. Otherwise, a new array is allocated with 148 * the runtime type of the specified array and the size of the specified collection. 149 * 150 * <p>If the collection fits in the specified array with room to spare (i.e., the array has more 151 * elements than the collection), the element in the array immediately following the end of the 152 * collection is set to {@code null}. This is useful in determining the length of the collection 153 * <i>only</i> if the caller knows that the collection does not contain any null elements. 154 */ 155 static <T extends @Nullable Object> T[] toArrayImpl( 156 @Nullable Object[] src, int offset, int len, T[] dst) { 157 checkPositionIndexes(offset, offset + len, src.length); 158 if (dst.length < len) { 159 dst = newArray(dst, len); 160 } else if (dst.length > len) { 161 @Nullable Object[] unsoundlyCovariantArray = dst; 162 unsoundlyCovariantArray[len] = null; 163 } 164 System.arraycopy(src, offset, dst, 0, len); 165 return dst; 166 } 167 168 /** 169 * Returns an array containing all of the elements in the specified collection. This method 170 * returns the elements in the order they are returned by the collection's iterator. The returned 171 * array is "safe" in that no references to it are maintained by the collection. The caller is 172 * thus free to modify the returned array. 173 * 174 * <p>This method assumes that the collection size doesn't change while the method is running. 175 * 176 * <p>TODO(kevinb): support concurrently modified collections? 177 * 178 * @param c the collection for which to return an array of elements 179 */ 180 static @Nullable Object[] toArrayImpl(Collection<?> c) { 181 return fillArray(c, new Object[c.size()]); 182 } 183 184 /** 185 * Returns a copy of the specified subrange of the specified array that is literally an Object[], 186 * and not e.g. a {@code String[]}. 187 */ 188 static @Nullable Object[] copyAsObjectArray(@Nullable Object[] elements, int offset, int length) { 189 checkPositionIndexes(offset, offset + length, elements.length); 190 if (length == 0) { 191 return new Object[0]; 192 } 193 @Nullable Object[] result = new Object[length]; 194 System.arraycopy(elements, offset, result, 0, length); 195 return result; 196 } 197 198 @CanIgnoreReturnValue 199 private static @Nullable Object[] fillArray(Iterable<?> elements, @Nullable Object[] array) { 200 int i = 0; 201 for (Object element : elements) { 202 array[i++] = element; 203 } 204 return array; 205 } 206 207 /** Swaps {@code array[i]} with {@code array[j]}. */ 208 static void swap(Object[] array, int i, int j) { 209 Object temp = array[i]; 210 array[i] = array[j]; 211 array[j] = temp; 212 } 213 214 @CanIgnoreReturnValue 215 static Object[] checkElementsNotNull(Object... array) { 216 return checkElementsNotNull(array, array.length); 217 } 218 219 @CanIgnoreReturnValue 220 static Object[] checkElementsNotNull(Object[] array, int length) { 221 for (int i = 0; i < length; i++) { 222 checkElementNotNull(array[i], i); 223 } 224 return array; 225 } 226 227 // We do this instead of Preconditions.checkNotNull to save boxing and array 228 // creation cost. 229 @CanIgnoreReturnValue 230 static Object checkElementNotNull(Object element, int index) { 231 if (element == null) { 232 throw new NullPointerException("at index " + index); 233 } 234 return element; 235 } 236}