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