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