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;
020import static java.lang.System.arraycopy;
021
022import com.google.common.annotations.GwtCompatible;
023import com.google.common.annotations.GwtIncompatible;
024import com.google.errorprone.annotations.CanIgnoreReturnValue;
025import java.lang.reflect.Array;
026import java.util.Arrays;
027import java.util.Collection;
028import org.checkerframework.checker.nullness.qual.NonNull;
029import org.checkerframework.checker.nullness.qual.Nullable;
030
031/**
032 * Static utility methods pertaining to object arrays.
033 *
034 * @author Kevin Bourrillion
035 * @since 2.0
036 */
037@GwtCompatible(emulated = true)
038@ElementTypesAreNonnullByDefault
039@SuppressWarnings("AvoidObjectArrays")
040public final class ObjectArrays {
041
042  private ObjectArrays() {}
043
044  /**
045   * Returns a new array of the given length with the specified component type.
046   *
047   * @param type the component type
048   * @param length the length of the new array
049   */
050  @GwtIncompatible // Array.newInstance(Class, int)
051  @SuppressWarnings("unchecked")
052  public static <T extends @Nullable Object> T[] newArray(Class<@NonNull T> type, int length) {
053    return (T[]) Array.newInstance(type, length);
054  }
055
056  /**
057   * Returns a new array of the given length with the same type as a reference array.
058   *
059   * @param reference any array of the desired type
060   * @param length the length of the new array
061   */
062  public static <T extends @Nullable Object> T[] newArray(T[] reference, int length) {
063    return Platform.newArray(reference, length);
064  }
065
066  /**
067   * Returns a new array that contains the concatenated contents of two arrays.
068   *
069   * @param first the first array of elements to concatenate
070   * @param second the second array of elements to concatenate
071   * @param type the component type of the returned array
072   */
073  @GwtIncompatible // Array.newInstance(Class, int)
074  public static <T extends @Nullable Object> T[] concat(
075      T[] first, T[] second, Class<@NonNull T> type) {
076    T[] result = newArray(type, first.length + second.length);
077    arraycopy(first, 0, result, 0, first.length);
078    arraycopy(second, 0, result, first.length, second.length);
079    return result;
080  }
081
082  /**
083   * Returns a new array that prepends {@code element} to {@code array}.
084   *
085   * @param element the element to prepend to the front of {@code array}
086   * @param array the array of elements to append
087   * @return an array whose size is one larger than {@code array}, with {@code element} occupying
088   *     the first position, and the elements of {@code array} occupying the remaining elements.
089   */
090  public static <T extends @Nullable Object> T[] concat(@ParametricNullness T element, T[] array) {
091    T[] result = newArray(array, array.length + 1);
092    result[0] = element;
093    arraycopy(array, 0, result, 1, array.length);
094    return result;
095  }
096
097  /**
098   * Returns a new array that appends {@code element} to {@code array}.
099   *
100   * @param array the array of elements to prepend
101   * @param element the element to append to the end
102   * @return an array whose size is one larger than {@code array}, with the same contents as {@code
103   *     array}, plus {@code element} occupying the last position.
104   */
105  public static <T extends @Nullable Object> T[] concat(T[] array, @ParametricNullness T element) {
106    T[] result = Arrays.copyOf(array, array.length + 1);
107    result[array.length] = element;
108    return result;
109  }
110
111  /**
112   * Returns an array containing all of the elements in the specified collection; the runtime type
113   * of the returned array is that of the specified array. If the collection fits in the specified
114   * array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the
115   * specified array and the size of the specified collection.
116   *
117   * <p>If the collection fits in the specified array with room to spare (i.e., the array has more
118   * elements than the collection), the element in the array immediately following the end of the
119   * collection is set to {@code null}. This is useful in determining the length of the collection
120   * <i>only</i> if the caller knows that the collection does not contain any null elements.
121   *
122   * <p>This method returns the elements in the order they are returned by the collection's
123   * iterator.
124   *
125   * <p>TODO(kevinb): support concurrently modified collections?
126   *
127   * @param c the collection for which to return an array of elements
128   * @param array the array in which to place the collection elements
129   * @throws ArrayStoreException if the runtime type of the specified array is not a supertype of
130   *     the runtime type of every element in the specified collection
131   */
132  static <T extends @Nullable Object> T[] toArrayImpl(Collection<?> c, T[] array) {
133    int size = c.size();
134    if (array.length < size) {
135      array = newArray(array, size);
136    }
137    fillArray(c, array);
138    if (array.length > size) {
139      @Nullable Object[] unsoundlyCovariantArray = array;
140      unsoundlyCovariantArray[size] = null;
141    }
142    return array;
143  }
144
145  /**
146   * Implementation of {@link Collection#toArray(Object[])} for collections backed by an object
147   * array. the runtime type of the returned array is that of the specified array. If the collection
148   * fits in the specified array, it is returned therein. Otherwise, a new array is allocated with
149   * the runtime type of the specified array and the size of the specified collection.
150   *
151   * <p>If the collection fits in the specified array with room to spare (i.e., the array has more
152   * elements than the collection), the element in the array immediately following the end of the
153   * collection is set to {@code null}. This is useful in determining the length of the collection
154   * <i>only</i> if the caller knows that the collection does not contain any null elements.
155   */
156  static <T extends @Nullable Object> T[] toArrayImpl(
157      @Nullable Object[] src, int offset, int len, T[] dst) {
158    checkPositionIndexes(offset, offset + len, src.length);
159    if (dst.length < len) {
160      dst = newArray(dst, len);
161    } else if (dst.length > len) {
162      @Nullable Object[] unsoundlyCovariantArray = dst;
163      unsoundlyCovariantArray[len] = null;
164    }
165    arraycopy(src, offset, dst, 0, len);
166    return dst;
167  }
168
169  /**
170   * Returns an array containing all of the elements in the specified collection. This method
171   * returns the elements in the order they are returned by the collection's iterator. The returned
172   * array is "safe" in that no references to it are maintained by the collection. The caller is
173   * thus free to modify the returned array.
174   *
175   * <p>This method assumes that the collection size doesn't change while the method is running.
176   *
177   * <p>TODO(kevinb): support concurrently modified collections?
178   *
179   * @param c the collection for which to return an array of elements
180   */
181  static @Nullable Object[] toArrayImpl(Collection<?> c) {
182    return fillArray(c, new Object[c.size()]);
183  }
184
185  /**
186   * Returns a copy of the specified subrange of the specified array that is literally an Object[],
187   * and not e.g. a {@code String[]}.
188   */
189  static @Nullable Object[] copyAsObjectArray(@Nullable Object[] elements, int offset, int length) {
190    checkPositionIndexes(offset, offset + length, elements.length);
191    if (length == 0) {
192      return new Object[0];
193    }
194    @Nullable Object[] result = new Object[length];
195    arraycopy(elements, offset, result, 0, length);
196    return result;
197  }
198
199  @CanIgnoreReturnValue
200  private static @Nullable Object[] fillArray(Iterable<?> elements, @Nullable Object[] array) {
201    int i = 0;
202    for (Object element : elements) {
203      array[i++] = element;
204    }
205    return array;
206  }
207
208  /** Swaps {@code array[i]} with {@code array[j]}. */
209  static void swap(Object[] array, int i, int j) {
210    Object temp = array[i];
211    array[i] = array[j];
212    array[j] = temp;
213  }
214
215  @CanIgnoreReturnValue
216  static Object[] checkElementsNotNull(Object... array) {
217    return checkElementsNotNull(array, array.length);
218  }
219
220  @CanIgnoreReturnValue
221  static Object[] checkElementsNotNull(Object[] array, int length) {
222    for (int i = 0; i < length; i++) {
223      checkElementNotNull(array[i], i);
224    }
225    return array;
226  }
227
228  // We do this instead of Preconditions.checkNotNull to save boxing and array
229  // creation cost.
230  @CanIgnoreReturnValue
231  static Object checkElementNotNull(Object element, int index) {
232    if (element == null) {
233      throw new NullPointerException("at index " + index);
234    }
235    return element;
236  }
237}