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/*
* Copyright (C) 2007 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.collect;
import com.google.common.base.Nullable;
import java.lang.reflect.Array;
import java.util.Arrays;
import java.util.Collection;
/**
* Static utility methods pertaining to object arrays.
*
* @author Kevin Bourrillion
*/
public final class ObjectArrays {
private ObjectArrays() {}
/**
* Returns a new array of the given length with the specified component type.
*
* @param type the component type
* @param length the length of the new array
*/
@SuppressWarnings("unchecked")
public static T[] newArray(Class type, int length) {
return (T[]) Array.newInstance(type, length);
}
/**
* Returns a new array of the given length with the same type as a reference
* array.
*
* @param reference any array of the desired type
* @param length the length of the new array
*/
public static T[] newArray(T[] reference, int length) {
Class type = reference.getClass().getComponentType();
// the cast is safe because result.getClass() == reference.getClass()
@SuppressWarnings("unchecked")
T[] result = (T[]) Array.newInstance(type, length);
return result;
}
/**
* Returns a new array that contains the concatenated contents of two arrays.
*
* @param first the first array of elements to concatenate
* @param second the second array of elements to concatenate
* @param type the component type of the returned array
*/
public static T[] concat(T[] first, T[] second, Class type) {
T[] result = newArray(type, first.length + second.length);
System.arraycopy(first, 0, result, 0, first.length);
System.arraycopy(second, 0, result, first.length, second.length);
return result;
}
/**
* Returns a new array that prepends {@code element} to {@code array}.
*
* @param element the element to prepend to the front of {@code array}
* @param array the array of elements to append
* @return an array whose size is one larger than {@code array}, with
* {@code element} occupying the first position, and the
* elements of {@code array} occupying the remaining elements.
*/
public static T[] concat(@Nullable T element, T[] array) {
@SuppressWarnings("unchecked")
T[] result =
(T[]) newArray(array.getClass().getComponentType(), array.length + 1);
result[0] = element;
System.arraycopy(array, 0, result, 1, array.length);
return result;
}
/**
* Returns a new array that appends {@code element} to {@code array}.
*
* @param array the array of elements to prepend
* @param element the element to append to the end
* @return an array whose size is one larger than {@code array}, with
* the same contents as {@code array}, plus {@code element} occupying the
* last position.
*/
public static T[] concat(T[] array, @Nullable T element) {
@SuppressWarnings("unchecked")
T[] result =
(T[]) newArray(array.getClass().getComponentType(), array.length + 1);
System.arraycopy(array, 0, result, 0, array.length);
result[array.length] = element;
return result;
}
/**
* Returns an array containing all of the elements in the specified
* collection; the runtime type of the returned array is that of the specified
* array. If the collection fits in the specified array, it is returned
* therein. Otherwise, a new array is allocated with the runtime type of the
* specified array and the size of the specified collection.
*
* If the collection fits in the specified array with room to spare (i.e.,
* the array has more elements than the collection), the element in the array
* immediately following the end of the collection is set to null. This is
* useful in determining the length of the collection only if the
* caller knows that the collection does not contain any null elements.
*
*
This method returns the elements in the order they are returned by the
* collection's iterator.
*
*
TODO: Support concurrent collections whose size can change while the
* method is running.
*
* @param c the collection for which to return an array of elements
* @param array the array in which to place the collection elements
* @throws ArrayStoreException if the runtime type of the specified array is
* not a supertype of the runtime type of every element in the specified
* collection
*/
static T[] toArrayImpl(Collection c, T[] array) {
int size = c.size();
if (array.length < size) {
array = newArray(array, size);
}
fillArray(c, array);
if (array.length > size) {
array[size] = null;
}
return array;
}
/**
* Returns an array containing all of the elements in the specified
* collection. This method returns the elements in the order they are returned
* by the collection's iterator. The returned array is "safe" in that no
* references to it are maintained by the collection. The caller is thus free
* to modify the returned array.
*
* This method assumes that the collection size doesn't change while the
* method is running.
*
*
TODO: Support concurrent collections whose size can change while the
* method is running.
*
* @param c the collection for which to return an array of elements
*/
static Object[] toArrayImpl(Collection c) {
return fillArray(c, new Object[c.size()]);
}
private static Object[] fillArray(Iterable elements, Object[] array) {
int i = 0;
for (Object element : elements) {
array[i++] = element;
}
return array;
}
}