253 lines
8.5 KiB
Java
253 lines
8.5 KiB
Java
/*
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* Copyright (C) 2007 The Guava Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.common.collect;
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import static com.google.common.base.Preconditions.checkPositionIndexes;
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import java.lang.reflect.Array;
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import java.util.Collection;
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import javax.annotation.Nullable;
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import com.google.common.annotations.GwtCompatible;
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import com.google.common.annotations.GwtIncompatible;
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/**
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* Static utility methods pertaining to object arrays.
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*
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* @author Kevin Bourrillion
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* @since 2.0 (imported from Google Collections Library)
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*/
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@GwtCompatible(emulated = true)
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public final class ObjectArrays {
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static final Object[] EMPTY_ARRAY = new Object[0];
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private ObjectArrays() {
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}
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/**
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* Returns a new array of the given length with the specified component type.
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*
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* @param type the component type
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* @param length the length of the new array
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*/
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@GwtIncompatible("Array.newInstance(Class, int)")
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@SuppressWarnings("unchecked")
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public static <T> T[] newArray(Class<T> type, int length) {
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return (T[]) Array.newInstance(type, length);
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}
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/**
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* Returns a new array of the given length with the same type as a reference
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* array.
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*
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* @param reference any array of the desired type
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* @param length the length of the new array
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*/
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public static <T> T[] newArray(T[] reference, int length) {
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return Platform.newArray(reference, length);
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}
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/**
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* Returns a new array that contains the concatenated contents of two arrays.
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*
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* @param first the first array of elements to concatenate
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* @param second the second array of elements to concatenate
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* @param type the component type of the returned array
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*/
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@GwtIncompatible("Array.newInstance(Class, int)")
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public static <T> T[] concat(T[] first, T[] second, Class<T> type) {
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T[] result = newArray(type, first.length + second.length);
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System.arraycopy(first, 0, result, 0, first.length);
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System.arraycopy(second, 0, result, first.length, second.length);
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return result;
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}
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/**
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* Returns a new array that prepends {@code element} to {@code array}.
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*
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* @param element the element to prepend to the front of {@code array}
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* @param array the array of elements to append
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* @return an array whose size is one larger than {@code array}, with
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* {@code element} occupying the first position, and the elements of
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* {@code array} occupying the remaining elements.
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*/
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public static <T> T[] concat(@Nullable T element, T[] array) {
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T[] result = newArray(array, array.length + 1);
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result[0] = element;
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System.arraycopy(array, 0, result, 1, array.length);
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return result;
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}
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/**
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* Returns a new array that appends {@code element} to {@code array}.
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*
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* @param array the array of elements to prepend
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* @param element the element to append to the end
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* @return an array whose size is one larger than {@code array}, with the same
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* contents as {@code array}, plus {@code element} occupying the last
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* position.
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*/
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public static <T> T[] concat(T[] array, @Nullable T element) {
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T[] result = arraysCopyOf(array, array.length + 1);
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result[array.length] = element;
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return result;
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}
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/** GWT safe version of Arrays.copyOf. */
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static <T> T[] arraysCopyOf(T[] original, int newLength) {
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T[] copy = newArray(original, newLength);
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System.arraycopy(original, 0, copy, 0, Math.min(original.length, newLength));
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return copy;
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}
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/**
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* Returns an array containing all of the elements in the specified collection;
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* the runtime type of the returned array is that of the specified array. If the
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* collection fits in the specified array, it is returned therein. Otherwise, a
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* new array is allocated with the runtime type of the specified array and the
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* size of the specified collection.
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*
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* <p>
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* If the collection fits in the specified array with room to spare (i.e., the
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* array has more elements than the collection), the element in the array
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* immediately following the end of the collection is set to {@code null}. This
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* is useful in determining the length of the collection <i>only</i> if the
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* caller knows that the collection does not contain any null elements.
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*
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* <p>
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* This method returns the elements in the order they are returned by the
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* collection's iterator.
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*
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* <p>
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* TODO(kevinb): support concurrently modified collections?
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*
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* @param c the collection for which to return an array of elements
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* @param array the array in which to place the collection elements
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* @throws ArrayStoreException if the runtime type of the specified array is not
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* a supertype of the runtime type of every element
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* in the specified collection
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*/
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static <T> T[] toArrayImpl(Collection<?> c, T[] array) {
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int size = c.size();
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if (array.length < size) {
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array = newArray(array, size);
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}
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fillArray(c, array);
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if (array.length > size) {
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array[size] = null;
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}
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return array;
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}
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/**
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* Implementation of {@link Collection#toArray(Object[])} for collections backed
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* by an object array. the runtime type of the returned array is that of the
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* specified array. If the collection fits in the specified array, it is
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* returned therein. Otherwise, a new array is allocated with the runtime type
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* of the specified array and the size of the specified collection.
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*
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* <p>
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* If the collection fits in the specified array with room to spare (i.e., the
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* array has more elements than the collection), the element in the array
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* immediately following the end of the collection is set to {@code null}. This
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* is useful in determining the length of the collection <i>only</i> if the
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* caller knows that the collection does not contain any null elements.
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*/
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static <T> T[] toArrayImpl(Object[] src, int offset, int len, T[] dst) {
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checkPositionIndexes(offset, offset + len, src.length);
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if (dst.length < len) {
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dst = newArray(dst, len);
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} else if (dst.length > len) {
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dst[len] = null;
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}
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System.arraycopy(src, offset, dst, 0, len);
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return dst;
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}
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/**
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* Returns an array containing all of the elements in the specified collection.
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* This method returns the elements in the order they are returned by the
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* collection's iterator. The returned array is "safe" in that no references to
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* it are maintained by the collection. The caller is thus free to modify the
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* returned array.
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*
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* <p>
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* This method assumes that the collection size doesn't change while the method
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* is running.
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*
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* <p>
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* TODO(kevinb): support concurrently modified collections?
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*
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* @param c the collection for which to return an array of elements
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*/
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static Object[] toArrayImpl(Collection<?> c) {
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return fillArray(c, new Object[c.size()]);
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}
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/**
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* Returns a copy of the specified subrange of the specified array that is
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* literally an Object[], and not e.g. a {@code String[]}.
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*/
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static Object[] copyAsObjectArray(Object[] elements, int offset, int length) {
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checkPositionIndexes(offset, offset + length, elements.length);
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if (length == 0) {
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return EMPTY_ARRAY;
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}
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Object[] result = new Object[length];
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System.arraycopy(elements, offset, result, 0, length);
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return result;
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}
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private static Object[] fillArray(Iterable<?> elements, Object[] array) {
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int i = 0;
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for (Object element : elements) {
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array[i++] = element;
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}
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return array;
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}
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/**
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* Swaps {@code array[i]} with {@code array[j]}.
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*/
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static void swap(Object[] array, int i, int j) {
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Object temp = array[i];
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array[i] = array[j];
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array[j] = temp;
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}
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static Object[] checkElementsNotNull(Object... array) {
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return checkElementsNotNull(array, array.length);
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}
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static Object[] checkElementsNotNull(Object[] array, int length) {
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for (int i = 0; i < length; i++) {
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checkElementNotNull(array[i], i);
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}
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return array;
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}
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// We do this instead of Preconditions.checkNotNull to save boxing and array
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// creation cost.
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static Object checkElementNotNull(Object element, int index) {
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if (element == null) {
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throw new NullPointerException("at index " + index);
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}
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return element;
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}
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}
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