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因为Arrays是JDK官方提供的操作数组的工具类,所以很多部分都是重载方法,本篇只举例说明,因为使用的方法是一致的。
public class Arrays {
// 最小数组长度,低于该最小数组长度,并行排序算法将不会进一步划分排序任务
private static final int MIN_ARRAY_SORT_GRAN = 1 << 13;
// 私有构造
private Arrays() {}
// 它实现了一个基团相互比较的元素的的自然顺序的比较器。
static final class NaturalOrder implements Comparator<Object> {
@SuppressWarnings("unchecked")
public int compare(Object first, Object second) {
return ((Comparable<Object>)first).compareTo(second);
}
static final NaturalOrder INSTANCE = new NaturalOrder();
}
// 将检查fromIndex和toIndex都在范围内,如果他们不抛出异常
private static void rangeCheck(int arrayLength, int fromIndex, int toIndex) {
if (fromIndex > toIndex) {
throw new IllegalArgumentException(
"fromIndex(" + fromIndex + ") > toIndex(" + toIndex + ")");
}
if (fromIndex < 0) {
throw new ArrayIndexOutOfBoundsException(fromIndex);
}
if (toIndex > arrayLength) {
throw new ArrayIndexOutOfBoundsException(toIndex);
}
}
// 排序 使用JDK提供的快排正序排序
public static void sort(int[] a) {
DualPivotQuicksort.sort(a, 0, a.length - 1, null, 0, 0);
}
// 省略其他重载方法 ...
// 平行划分排序 分治合并思想
public static void parallelSort(byte[] a) {
int n = a.length, p, g;
if (n <= MIN_ARRAY_SORT_GRAN ||
(p = ForkJoinPool.getCommonPoolParallelism()) == 1)
DualPivotQuicksort.sort(a, 0, n - 1);
else
new ArraysParallelSortHelpers.FJByte.Sorter
(null, a, new byte[n], 0, n, 0,
((g = n / (p << 2)) <= MIN_ARRAY_SORT_GRAN) ?
MIN_ARRAY_SORT_GRAN : g).invoke();
}
// 省略其他重载方法 ...
// 老归并排序实现可以使用系统属性中选择(与破碎比较兼容性)。
// 不能在封闭类的静态布尔由于循环依赖。 为了在未来的版本中删除
static final class LegacyMergeSort {
private static final boolean userRequested =
java.security.AccessController.doPrivileged(
new sun.security.action.GetBooleanAction(
"java.util.Arrays.useLegacyMergeSort")).booleanValue();
}
// 调用归并排序
private static void legacyMergeSort(Object[] a) {
Object[] aux = a.clone();
mergeSort(aux, a, 0, a.length, 0);
}
// 协调参数:在等于或低于其插入排序列表大小将优先于归并使用
private static final int INSERTIONSORT_THRESHOLD = 7;
// 归并排序算法
private static void mergeSort(Object[] src,
Object[] dest,
int low,
int high,
int off) {
int length = high - low;
// Insertion sort on smallest arrays
if (length < INSERTIONSORT_THRESHOLD) {
for (int i=low; i<high; i++)
for (int j=i; j>low &&
((Comparable) dest[j-1]).compareTo(dest[j])>0; j--)
swap(dest, j, j-1);
return;
}
// Recursively sort halves of dest into src
int destLow = low;
int destHigh = high;
low += off;
high += off;
int mid = (low + high) >>> 1;
mergeSort(dest, src, low, mid, -off);
mergeSort(dest, src, mid, high, -off);
if (((Comparable)src[mid-1]).compareTo(src[mid]) <= 0) {
System.arraycopy(src, low, dest, destLow, length);
return;
}
// Merge sorted halves (now in src) into dest
for(int i = destLow, p = low, q = mid; i < destHigh; i++) {
if (q >= high || p < mid && ((Comparable)src[p]).compareTo(src[q])<=0)
dest[i] = src[p++];
else
dest[i] = src[q++];
}
}
// 交换数据
private static void swap(Object[] x, int a, int b) {
Object t = x[a];
x[a] = x[b];
x[b] = t;
}
public static <T> void parallelPrefix(T[] array, BinaryOperator<T> op) {
Objects.requireNonNull(op);
if (array.length > 0)
new ArrayPrefixHelpers.CumulateTask<>
(null, op, array, 0, array.length).invoke();
}
// 重载方法省略 ....
// 二分查找算法
public static int binarySearch(long[] a, long key) {
return binarySearch0(a, 0, a.length, key);
}
// 核心二分算法
private static int binarySearch0(long[] a, int fromIndex, int toIndex,
long key) {
int low = fromIndex;
int high = toIndex - 1;
while (low <= high) {
int mid = (low + high) >>> 1;
long midVal = a[mid];
if (midVal < key)
low = mid + 1;
else if (midVal > key)
high = mid - 1;
else
return mid; // key found
}
return -(low + 1); // key not found.
}
// 重载方法省略 ....
// equals 方法
public static boolean equals(long[] a, long[] a2) {
if (a==a2)
return true;
if (a==null || a2==null)
return false;
int length = a.length;
if (a2.length != length)
return false;
for (int i=0; i<length; i++)
if (a[i] != a2[i])
return false;
return true;
}
// 重载方法省略 ....
// 填充数组 a 填充为 val
public static void fill(long[] a, long val) {
for (int i = 0, len = a.length; i < len; i++)
a[i] = val;
}
// 重载方法省略 ....
// 数组拷贝 复制指定的数组,截取或用null填充(如果必要)
public static <T> T[] copyOf(T[] original, int newLength) {
return (T[]) copyOf(original, newLength, original.getClass());
}
// 调用 System.arraycopy()
public static <T,U> T[] copyOf(U[] original, int newLength, Class<? extends T[]> newType) {
@SuppressWarnings("unchecked")
T[] copy = ((Object)newType == (Object)Object[].class)
? (T[]) new Object[newLength]
: (T[]) Array.newInstance(newType.getComponentType(), newLength);
System.arraycopy(original, 0, copy, 0,
Math.min(original.length, newLength));
return copy;
}
// 重载方法省略 ....
// 复制指定的范围指定数组到一个新的数组
public static <T> T[] copyOfRange(T[] original, int from, int to) {
return copyOfRange(original, from, to, (Class<? extends T[]>) original.getClass());
}
public static <T,U> T[] copyOfRange(U[] original, int from, int to, Class<? extends T[]> newType) {
int newLength = to - from;
if (newLength < 0)
throw new IllegalArgumentException(from + " > " + to);
@SuppressWarnings("unchecked")
T[] copy = ((Object)newType == (Object)Object[].class)
? (T[]) new Object[newLength]
: (T[]) Array.newInstance(newType.getComponentType(), newLength);
System.arraycopy(original, from, copy, 0,
Math.min(original.length - from, newLength));
return copy;
}
// 重载方法省略 ....
// 返回List数组 调用 下面的 ArrayList<>
public static <T> List<T> asList(T... a) {
return new ArrayList<>(a);
}
private static class ArrayList<E> extends AbstractList<E>
implements RandomAccess, java.io.Serializable
{
private static final long serialVersionUID = -2764017481108945198L;
private final E[] a;
ArrayList(E[] array) {
a = Objects.requireNonNull(array);
}
@Override
public int size() {
return a.length;
}
@Override
public Object[] toArray() {
return a.clone();
}
@Override
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
int size = size();
if (a.length < size)
return Arrays.copyOf(this.a, size,
(Class<? extends T[]>) a.getClass());
System.arraycopy(this.a, 0, a, 0, size);
if (a.length > size)
a[size] = null;
return a;
}
@Override
public E get(int index) {
return a[index];
}
@Override
public E set(int index, E element) {
E oldValue = a[index];
a[index] = element;
return oldValue;
}
@Override
public int indexOf(Object o) {
E[] a = this.a;
if (o == null) {
for (int i = 0; i < a.length; i++)
if (a[i] == null)
return i;
} else {
for (int i = 0; i < a.length; i++)
if (o.equals(a[i]))
return i;
}
return -1;
}
@Override
public boolean contains(Object o) {
return indexOf(o) != -1;
}
@Override
public Spliterator<E> spliterator() {
return Spliterators.spliterator(a, Spliterator.ORDERED);
}
@Override
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
for (E e : a) {
action.accept(e);
}
}
@Override
public void replaceAll(UnaryOperator<E> operator) {
Objects.requireNonNull(operator);
E[] a = this.a;
for (int i = 0; i < a.length; i++) {
a[i] = operator.apply(a[i]);
}
}
@Override
public void sort(Comparator<? super E> c) {
Arrays.sort(a, c);
}
}
// hashCode
public static int hashCode(long a[]) {
if (a == null)
return 0;
int result = 1;
for (long element : a) {
int elementHash = (int)(element ^ (element >>> 32));
result = 31 * result + elementHash;
}
return result;
}
// 省略重载方法 ...
// 深度 HashCode
// 返回基于指定数组的“深层内容”哈希码
public static int deepHashCode(Object a[]) {
if (a == null)
return 0;
int result = 1;
for (Object element : a) {
int elementHash = 0;
if (element instanceof Object[])
elementHash = deepHashCode((Object[]) element);
else if (element instanceof byte[])
elementHash = hashCode((byte[]) element);
else if (element instanceof short[])
elementHash = hashCode((short[]) element);
else if (element instanceof int[])
elementHash = hashCode((int[]) element);
else if (element instanceof long[])
elementHash = hashCode((long[]) element);
else if (element instanceof char[])
elementHash = hashCode((char[]) element);
else if (element instanceof float[])
elementHash = hashCode((float[]) element);
else if (element instanceof double[])
elementHash = hashCode((double[]) element);
else if (element instanceof boolean[])
elementHash = hashCode((boolean[]) element);
else if (element != null)
elementHash = element.hashCode();
result = 31 * result + elementHash;
}
return result;
}
// 深度比较
public static boolean deepEquals(Object[] a1, Object[] a2) {
if (a1 == a2)
return true;
if (a1 == null || a2==null)
return false;
int length = a1.length;
if (a2.length != length)
return false;
for (int i = 0; i < length; i++) {
Object e1 = a1[i];
Object e2 = a2[i];
if (e1 == e2)
continue;
if (e1 == null)
return false;
// Figure out whether the two elements are equal
boolean eq = deepEquals0(e1, e2);
if (!eq)
return false;
}
return true;
}
// 辅助方法
static boolean deepEquals0(Object e1, Object e2) {
assert e1 != null;
boolean eq;
if (e1 instanceof Object[] && e2 instanceof Object[])
eq = deepEquals ((Object[]) e1, (Object[]) e2);
else if (e1 instanceof byte[] && e2 instanceof byte[])
eq = equals((byte[]) e1, (byte[]) e2);
else if (e1 instanceof short[] && e2 instanceof short[])
eq = equals((short[]) e1, (short[]) e2);
else if (e1 instanceof int[] && e2 instanceof int[])
eq = equals((int[]) e1, (int[]) e2);
else if (e1 instanceof long[] && e2 instanceof long[])
eq = equals((long[]) e1, (long[]) e2);
else if (e1 instanceof char[] && e2 instanceof char[])
eq = equals((char[]) e1, (char[]) e2);
else if (e1 instanceof float[] && e2 instanceof float[])
eq = equals((float[]) e1, (float[]) e2);
else if (e1 instanceof double[] && e2 instanceof double[])
eq = equals((double[]) e1, (double[]) e2);
else if (e1 instanceof boolean[] && e2 instanceof boolean[])
eq = equals((boolean[]) e1, (boolean[]) e2);
else
eq = e1.equals(e2);
return eq;
}
// toString 方法
public static String toString(long[] a) {
if (a == null)
return "null";
int iMax = a.length - 1;
if (iMax == -1)
return "[]";
StringBuilder b = new StringBuilder();
b.append('[');
for (int i = 0; ; i++) {
b.append(a[i]);
if (i == iMax)
return b.append(']').toString();
b.append(", ");
}
}
// 省略重载方法 ...
// 深度 toString
public static String deepToString(Object[] a) {
if (a == null)
return "null";
int bufLen = 20 * a.length;
if (a.length != 0 && bufLen <= 0)
bufLen = Integer.MAX_VALUE;
StringBuilder buf = new StringBuilder(bufLen);
deepToString(a, buf, new HashSet<Object[]>());
return buf.toString();
}
// 省略重载方法 ...
// 置指定的数组中的所有元素,使用所提供的生成器函数来计算每个元素。
public static <T> void setAll(T[] array, IntFunction<? extends T> generator) {
Objects.requireNonNull(generator);
for (int i = 0; i < array.length; i++)
array[i] = generator.apply(i);
}
// 设置指定的数组的所有元素,并行地使用所提供的生成器函数来计算每个元素。
public static <T> void parallelSetAll(T[] array, IntFunction<? extends T> generator) {
Objects.requireNonNull(generator);
IntStream.range(0, array.length).parallel().forEach(i -> { array[i] = generator.apply(i); });
}
// 返回一个Spliterator覆盖所有指定数组
public static <T> Spliterator<T> spliterator(T[] array) {
return Spliterators.spliterator(array,
Spliterator.ORDERED | Spliterator.IMMUTABLE);
}
// 返回一个Spliterator.OfInt覆盖所有指定数组
public static Spliterator.OfInt spliterator(int[] array) {
return Spliterators.spliterator(array,
Spliterator.ORDERED | Spliterator.IMMUTABLE);
}
// JDK8 新特性 Stream 流
public static <T> Stream<T> stream(T[] array, int startInclusive, int endExclusive) {
return StreamSupport.stream(spliterator(array, startInclusive, endExclusive), false);
}
}
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