4.6.5 Java8增强的工具类 Arrays

发表于 2020-01-28 更新于 2021-11-18 分类于 1 疯狂Java讲义 (第4版) ，第4章流酲控制与数组， 4.6 深入数组 Waline：本文字数： 22k 阅读时长 ≈ 20 分钟

4.6.5 Java8增强的工具类 Arrays

Java提供的Arrays类里包含的一些static修饰的方法可以直接操作数组,这个Arrays类里包含了如下几个static修饰的方法(static修饰的方法可以直接通过类名调用)。
未完待续…

程序示例

下面程序示范了Arrays类的用法:

Java8增强的Arrays方法

Java8增强了Arrays类的功能,为Arrays类增加了一些工具方法,这些工具方法可以充分利用**多CPU**并行的能力来提高设值、排序的性能。下面是Java8为Arrays类增加的工具方法。

binarySearch方法

方法	描述
`static int binarySearch(byte[] a, byte key)`	使用二分法查询`key`元素值在a数组中出现的索引;如果a数组不包含`key`元素值,则返回负数。调用该方法时要求数组中元素已经按升序排列,这样才能得到正确结果
`static int binarySearch(byte[] a, int fromIndex, int toIndex, byte key)`	这个方法与前一个方法类似,但它只搜索a数组中`fromIndex`到`tolndex`索引的元素。调用该方法时要求数组中元素已经按升序排列,这样才能得到正确结果。
`static int binarySearch(char[] a, char key)`	Searches the specified array of chars for the specified value using the binary search algorithm.
`static int binarySearch(char[] a, int fromIndex, int toIndex, char key)`	Searches a range of the specified array of chars for the specified value using the binary search algorithm.
`static int binarySearch(double[] a, double key)`	Searches the specified array of doubles for the specified value using the binary search algorithm.
`static int binarySearch(double[] a, int fromIndex, int toIndex, double key)`	Searches a range of the specified array of doubles for the specified value using the binary search algorithm.
`static int binarySearch(float[] a, float key)`	Searches the specified array of floats for the specified value using the binary search algorithm.
`static int binarySearch(float[] a, int fromIndex, int toIndex, float key)`	Searches a range of the specified array of floats for the specified value using the binary search algorithm.
`static int binarySearch(int[] a, int key)`	Searches the specified array of ints for the specified value using the binary search algorithm.
`static int binarySearch(int[] a, int fromIndex, int toIndex, int key)`	Searches a range of the specified array of ints for the specified value using the binary search algorithm.
`static int binarySearch(long[] a, int fromIndex, int toIndex, long key)`	Searches a range of the specified array of longs for the specified value using the binary search algorithm.
`static int binarySearch(long[] a, long key)`	Searches the specified array of longs for the specified value using the binary search algorithm.
`static int binarySearch(short[] a, int fromIndex, int toIndex, short key)`	Searches a range of the specified array of shorts for the specified value using the binary search algorithm.
`static int binarySearch(short[] a, short key)`	Searches the specified array of shorts for the specified value using the binary search algorithm.
`static int binarySearch(Object[] a, int fromIndex, int toIndex, Object key)`	Searches a range of the specified array for the specified object using the binary search algorithm.
`static int binarySearch(Object[] a, Object key)`	Searches the specified array for the specified object using the binary search algorithm.
`static <T> int binarySearch(T[] a, int fromIndex, int toIndex, T key, Comparator<? super T> c)`	Searches a range of the specified array for the specified object using the binary search algorithm.
`static <T> int binarySearch(T[] a, T key, Comparator<? super T> c)`	Searches the specified array for the specified object using the binary search algorithm.

copyOf方法

方法	描述
`static boolean[] copyOf(boolean[] original, int newLength)`	这个方法将会把`original`数组复制成一个新数组,其中`length`是新数组的长度。如果`length`小于`original`数组的长度,则新数组就是原数组的前面`length`个元素;如果`length`大于`original`数组的长度,则新数组的前面元素就是原数组的所有元素,后面补充0(数值类型)、`false`(布尔类型)或者`null`(引用类型)
`static byte[] copyOf(byte[] original, int newLength)`	Copies the specified array, truncating or padding with zeros (if necessary) so the copy has the specified length.
`static char[] copyOf(char[] original, int newLength)`	Copies the specified array, truncating or padding with null characters (if necessary) so the copy has the specified length.
`static double[] copyOf(double[] original, int newLength)`	Copies the specified array, truncating or padding with zeros (if necessary) so the copy has the specified length.
`static float[] copyOf(float[] original, int newLength)`	Copies the specified array, truncating or padding with zeros (if necessary) so the copy has the specified length.
`static int[] copyOf(int[] original, int newLength)`	Copies the specified array, truncating or padding with zeros (if necessary) so the copy has the specified length.
`static long[] copyOf(long[] original, int newLength)`	Copies the specified array, truncating or padding with zeros (if necessary) so the copy has the specified length.
`static short[] copyOf(short[] original, int newLength)`	Copies the specified array, truncating or padding with zeros (if necessary) so the copy has the specified length.
`static <T> T[] copyOf(T[] original, int newLength)`	Copies the specified array, truncating or padding with nulls (if necessary) so the copy has the specified length.
`static <T,U> T[] copyOf(U[] original, int newLength, Class<? extends T[]> newType)`	Copies the specified array, truncating or padding with nulls (if necessary) so the copy has the specified length.

copyOfRange方法

方法	描述
`static boolean[] copyOfRange(boolean[] original, int from, int to)`	这个方法与前面方法相似,但这个方法只复制`original`数组的`from`索引到`to`索引的元素。
`static byte[] copyOfRange(byte[] original, int from, int to)`	Copies the specified range of the specified array into a new array.
`static char[] copyOfRange(char[] original, int from, int to)`	Copies the specified range of the specified array into a new array.
`static double[] copyOfRange(double[] original, int from, int to)`	Copies the specified range of the specified array into a new array.
`static float[] copyOfRange(float[] original, int from, int to)`	Copies the specified range of the specified array into a new array.
`static int[] copyOfRange(int[] original, int from, int to)`	Copies the specified range of the specified array into a new array.
`static long[] copyOfRange(long[] original, int from, int to)`	Copies the specified range of the specified array into a new array.
`static short[] copyOfRange(short[] original, int from, int to)`	Copies the specified range of the specified array into a new array.
`static <T> T[] copyOfRange(T[] original, int from, int to)`	Copies the specified range of the specified array into a new array.
`static <T,U> T[] copyOfRange(U[] original, int from, int to, Class<? extends T[]> newType)`	Copies the specified range of the specified array into a new array.

fill方法

方法	描述
`static void fill(boolean[] a, boolean val)`	该方法将会把a数组的所有元素都赋值为`val`
`static void fill(boolean[] a, int fromIndex, int toIndex, boolean val)`	该方法与前一个方法的作用相同,区别只是该方法仅仅将a数组的`fromIndex`到`toIndex`索引的数组元素赋值为`val`
`static void fill(byte[] a, byte val)`	Assigns the specified byte value to each element of the specified array of bytes.
`static void fill(byte[] a, int fromIndex, int toIndex, byte val)`	Assigns the specified byte value to each element of the specified range of the specified array of bytes.
`static void fill(char[] a, char val)`	Assigns the specified char value to each element of the specified array of chars.
`static void fill(char[] a, int fromIndex, int toIndex, char val)`	Assigns the specified char value to each element of the specified range of the specified array of chars.
`static void fill(double[] a, double val)`	Assigns the specified double value to each element of the specified array of doubles.
`static void fill(double[] a, int fromIndex, int toIndex, double val)`	Assigns the specified double value to each element of the specified range of the specified array of doubles.
`static void fill(float[] a, float val)`	Assigns the specified float value to each element of the specified array of floats.
`static void fill(float[] a, int fromIndex, int toIndex, float val)`	Assigns the specified float value to each element of the specified range of the specified array of floats.
`static void fill(int[] a, int val)`	Assigns the specified int value to each element of the specified array of ints.
`static void fill(int[] a, int fromIndex, int toIndex, int val)`	Assigns the specified int value to each element of the specified range of the specified array of ints.
`static void fill(long[] a, int fromIndex, int toIndex, long val)`	Assigns the specified long value to each element of the specified range of the specified array of longs.
`static void fill(long[] a, long val)`	Assigns the specified long value to each element of the specified array of longs.
`static void fill(short[] a, int fromIndex, int toIndex, short val)`	Assigns the specified short value to each element of the specified range of the specified array of shorts.
`static void fill(short[] a, short val)`	Assigns the specified short value to each element of the specified array of shorts.
`static void fill(Object[] a, int fromIndex, int toIndex, Object val)`	Assigns the specified Object reference to each element of the specified range of the specified array of Objects.
`static void fill(Object[] a, Object val)`	Assigns the specified Object reference to each element of the specified array of Objects.

sort方法

方法	描述
`static void sort(byte[] a)`	该方法对a数组的数组元素进行排序
`static void sort(byte[] a, int fromIndex, int toIndex)`	该方法与前一个方法相似,区别是该方法仅仅对`fromIndex`到`toIndex`索引的元素进行排序。
`static void sort(char[] a)`	Sorts the specified array into ascending numerical order.
`static void sort(char[] a, int fromIndex, int toIndex)`	Sorts the specified range of the array into ascending order.
`static void sort(double[] a)`	Sorts the specified array into ascending numerical order.
`static void sort(double[] a, int fromIndex, int toIndex)`	Sorts the specified range of the array into ascending order.
`static void sort(float[] a)`	Sorts the specified array into ascending numerical order.
`static void sort(float[] a, int fromIndex, int toIndex)`	Sorts the specified range of the array into ascending order.
`static void sort(int[] a)`	Sorts the specified array into ascending numerical order.
`static void sort(int[] a, int fromIndex, int toIndex)`	Sorts the specified range of the array into ascending order.
`static void sort(long[] a)`	Sorts the specified array into ascending numerical order.
`static void sort(long[] a, int fromIndex, int toIndex)`	Sorts the specified range of the array into ascending order.
`static void sort(short[] a)`	Sorts the specified array into ascending numerical order.
`static void sort(short[] a, int fromIndex, int toIndex)`	Sorts the specified range of the array into ascending order.
`static void sort(Object[] a)`	Sorts the specified array of objects into ascending order, according to the natural ordering of its elements.
`static void sort(Object[] a, int fromIndex, int toIndex)`	Sorts the specified range of the specified array of objects into ascending order, according to the natural ordering of its elements.
`static <T> void sort(T[] a, int fromIndex, int toIndex, Comparator<? super T> c)`	Sorts the specified range of the specified array of objects according to the order induced by the specified comparator.
`static <T> void sort(T[] a, Comparator<? super T> c)`	Sorts the specified array of objects according to the order induced by the specified comparator.

equals方法

方法	描述
`static boolean equals(boolean[] a, boolean[] a2)`	如果a数组和`a2`数组的长度相等,而且a数组和`a2`数组的数组元素也一一相同,该方法将返回`true`。
`static boolean equals(boolean[] a, int aFromIndex, int aToIndex, boolean[] b, int bFromIndex, int bToIndex)`	Returns true if the two specified arrays of booleans, over the specified ranges, are equal to one another.
`static boolean equals(byte[] a, byte[] a2)`	Returns true if the two specified arrays of bytes are equal to one another.
`static boolean equals(byte[] a, int aFromIndex, int aToIndex, byte[] b, int bFromIndex, int bToIndex)`	Returns true if the two specified arrays of bytes, over the specified ranges, are equal to one another.
`static boolean equals(char[] a, char[] a2)`	Returns true if the two specified arrays of chars are equal to one another.
`static boolean equals(char[] a, int aFromIndex, int aToIndex, char[] b, int bFromIndex, int bToIndex)`	Returns true if the two specified arrays of chars, over the specified ranges, are equal to one another.
`static boolean equals(double[] a, double[] a2)`	Returns true if the two specified arrays of doubles are equal to one another.
`static boolean equals(double[] a, int aFromIndex, int aToIndex, double[] b, int bFromIndex, int bToIndex)`	Returns true if the two specified arrays of doubles, over the specified ranges, are equal to one another.
`static boolean equals(float[] a, float[] a2)`	Returns true if the two specified arrays of floats are equal to one another.
`static boolean equals(float[] a, int aFromIndex, int aToIndex, float[] b, int bFromIndex, int bToIndex)`	Returns true if the two specified arrays of floats, over the specified ranges, are equal to one another.
`static boolean equals(int[] a, int[] a2)`	Returns true if the two specified arrays of ints are equal to one another.
`static boolean equals(int[] a, int aFromIndex, int aToIndex, int[] b, int bFromIndex, int bToIndex)`	Returns true if the two specified arrays of ints, over the specified ranges, are equal to one another.
`static boolean equals(long[] a, int aFromIndex, int aToIndex, long[] b, int bFromIndex, int bToIndex)`	Returns true if the two specified arrays of longs, over the specified ranges, are equal to one another.
`static boolean equals(long[] a, long[] a2)`	Returns true if the two specified arrays of longs are equal to one another.
`static boolean equals(short[] a, int aFromIndex, int aToIndex, short[] b, int bFromIndex, int bToIndex)`	Returns true if the two specified arrays of shorts, over the specified ranges, are equal to one another.
`static boolean equals(short[] a, short[] a2)`	Returns true if the two specified arrays of shorts are equal to one another.
`static boolean equals(Object[] a, int aFromIndex, int aToIndex, Object[] b, int bFromIndex, int bToIndex)`	Returns true if the two specified arrays of Objects, over the specified ranges, are equal to one another.
`static boolean equals(Object[] a, Object[] a2)`	Returns true if the two specified arrays of Objects are equal to one another.
`static <T> boolean equals(T[] a, int aFromIndex, int aToIndex, T[] b, int bFromIndex, int bToIndex, Comparator<? super T> cmp)`	Returns true if the two specified arrays of Objects, over the specified ranges, are equal to one another.
`static <T> boolean equals(T[] a, T[] a2, Comparator<? super T> cmp)`	Returns true if the two specified arrays of Objects are equal to one another.

toString方法

方法	描述
`static String toString(boolean[] a)`	该方法将一个数组转换成一个字符串。该方法按顺序把多个数组元素连缀在一起,多个数组元素使用英文逗号(,)和空格隔开。
`static String toString(byte[] a)`	Returns a string representation of the contents of the specified array.
`static String toString(char[] a)`	Returns a string representation of the contents of the specified array.
`static String toString(double[] a)`	Returns a string representation of the contents of the specified array.
`static String toString(float[] a)`	Returns a string representation of the contents of the specified array.
`static String toString(int[] a)`	Returns a string representation of the contents of the specified array.
`static String toString(long[] a)`	Returns a string representation of the contents of the specified array.
`static String toString(short[] a)`	Returns a string representation of the contents of the specified array.
`static String toString(Object[] a)`	Returns a string representation of the contents of the specified array.

程序示例 Arrays类Java8新增方法

下面程序示范了Java8为Arrays类新增的方法:

import java.util.Arrays;

public class ArraysTest {
    public static void main(String[] args) {
        // 定义一个a数组
        int[] a = new int[] { 3, 4, 5, 6 };
        // 定义一个a2数组
        int[] a2 = new int[] { 3, 4, 5, 6 };
        // a数组和a2数组的长度相等，每个元素依次相等，将输出true
        System.out.println("a数组和a2数组是否相等：" + Arrays.equals(a, a2));
        // 通过复制a数组，生成一个新的b数组
        int[] b = Arrays.copyOf(a, 6);
        System.out.println("a数组和b数组是否相等：" + Arrays.equals(a, b));
        // 输出b数组的元素，将输出[3, 4, 5, 6, 0, 0]
        System.out.println("b数组的元素为：" + Arrays.toString(b));
        // 将b数组的第3个元素（包括）到第5个元素（不包括）赋为1
        Arrays.fill(b, 2, 4, 1);
        // 输出b数组的元素，将输出[3, 4, 1, 1, 0, 0]
        System.out.println("b数组的元素为：" + Arrays.toString(b));
        // 对b数组进行排序
        Arrays.sort(b);
        // 输出b数组的元素，将输出[0, 0, 1, 1, 3, 4]
        System.out.println("b数组的元素为：" + Arrays.toString(b));
    }
}

System类的arrayCopy复制数组

除此之外,在System类里也包含了一个arrayCopy方法,该方法可以将src数组里的元素值赋给dest数组的元素,其中srcPos指定从src数组的第几个元素开始赋值,length参数指定将src数组的多少个元素值赋给dest数组的元素。

方法	描述
`static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length)`	Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array.

java8新增方法

Java8增强了Arrays类的功能,为Arrays类增加了一些工具方法,这些工具方法可以充分利用多CPU并行的能力来提高设值、排序的性能。下面是Java8为Arrays类增加的工具方法。
下面的方法中,所有以parallel开头的方法都表示该方法可利用CPU并行的能力来提高性能

parallelPrefix方法
setAll方法
parallelSetAll方法
parallelSort方法
spliterator方法
stream方法

parallelPrefix方法

方法	描述
`static void parallelPrefix(double[] array, DoubleBinaryOperator op)`	该方法使用`op`参数指定的计算公式计算得到的结果作为新的元素。`op`计算公式包括`let`、`right`两个形参,其中`left`代表数组中前一个索引处的元素,`ight`代表数组中当前索引处的元素,当计算第一个新数组元素时,`left`的值默认为1
`static void parallelPrefix(double[] array, int fromIndex, int toIndex, DoubleBinaryOperator op)`	该方法与上一个方法相似,区别是该方法仅重新计算`fromIndex`到`tolndex`索引的元素。
`static void parallelPrefix(int[] array, int fromIndex, int toIndex, IntBinaryOperator op)`	Performs parallelPrefix(int[], IntBinaryOperator) for the given subrange of the array.
`static void parallelPrefix(int[] array, IntBinaryOperator op)`	Cumulates, in parallel, each element of the given array in place, using the supplied function.
`static void parallelPrefix(long[] array, int fromIndex, int toIndex, LongBinaryOperator op)`	Performs parallelPrefix(long[], LongBinaryOperator) for the given subrange of the array.
`static void parallelPrefix(long[] array, LongBinaryOperator op)`	Cumulates, in parallel, each element of the given array in place, using the supplied function.
`static <T> void parallelPrefix(T[] array, int fromIndex, int toIndex, BinaryOperator<T> op)`	Performs parallelPrefix(Object[], BinaryOperator) for the given subrange of the array.
`static <T> void parallelPrefix(T[] array, BinaryOperator<T> op)`	Cumulates, in parallel, each element of the given array in place, using the supplied function.

setAll方法

方法	描述
`static void setAll(double[] array, IntToDoubleFunction generator)`	该方法使用指定的生成器(`generator`)为所有数组元素设置值,该生成器控制数组元素的值的生成算法。
`static void setAll(long[] array, IntToLongFunction generator)`	Set all elements of the specified array, using the provided generator function to compute each element.
`static void setAll(int[] array, IntUnaryOperator generator)`	Set all elements of the specified array, using the provided generator function to compute each element.
`static <T> void setAll(T[] array, IntFunction<? extends T> generator)`	Set all elements of the specified array, using the provided generator function to compute each element.

parallelSetAll方法

方法	描述
`static void parallelSetAll(double[] array, IntToDoubleFunction generator)`	该方法的功能与上一个方法相同,只是该方法增加了并行能力,可以利用多`CPU`并行来提高性能
`static void parallelSetAll(int[] array, IntUnaryOperator generator)`	Set all elements of the specified array, in parallel, using the provided generator function to compute each element.
`static void parallelSetAll(long[] array, IntToLongFunction generator)`	Set all elements of the specified array, in parallel, using the provided generator function to compute each element.
`static <T> void parallelSetAll(T[] array, IntFunction<? extends T> generator)`	Set all elements of the specified array, in parallel, using the provided generator function to compute each element.

parallelSort方法

方法	描述
`static void parallelSort(byte[] a)`该方法的功能与`Arrays`类以前就有的`sort()`方法相似,只是该方法增加了并行能力,可以利用多`CPU`并行来提高性能。
`static void parallelSort(byte[] a, int fromIndex, int toIndex)`	该方法与上一个方法相似,区别是该方法仅加了并行能力,可以利用多`CPU`并行来提高性能。
`static void parallelSort(char[] a)`	Sorts the specified array into ascending numerical order.
`static void parallelSort(char[] a, int fromIndex, int toIndex)`	Sorts the specified range of the array into ascending numerical order.
`static void parallelSort(double[] a)`	Sorts the specified array into ascending numerical order.
`static void parallelSort(double[] a, int fromIndex, int toIndex)`	Sorts the specified range of the array into ascending numerical order.
`static void parallelSort(float[] a)`	Sorts the specified array into ascending numerical order.
`static void parallelSort(float[] a, int fromIndex, int toIndex)`	Sorts the specified range of the array into ascending numerical order.
`static void parallelSort(int[] a)`	Sorts the specified array into ascending numerical order.
`static void parallelSort(int[] a, int fromIndex, int toIndex)`	Sorts the specified range of the array into ascending numerical order.
`static void parallelSort(long[] a)`	Sorts the specified array into ascending numerical order.
`static void parallelSort(long[] a, int fromIndex, int toIndex)`	Sorts the specified range of the array into ascending numerical order.
`static void parallelSort(short[] a)`	Sorts the specified array into ascending numerical order.
`static void parallelSort(short[] a, int fromIndex, int toIndex)`	Sorts the specified range of the array into ascending numerical order.
`static <T extends Comparable<? super T>>`	void parallelSort(T[] a)
`Sorts the specified array of objects into ascending order, according to the natural ordering of its elements.`	static <T extends Comparable<? super T>>
`void parallelSort(T[] a, int fromIndex, int toIndex)`	Sorts the specified range of the specified array of objects into ascending order, according to the natural ordering of its elements.
`static <T> void parallelSort(T[] a, int fromIndex, int toIndex, Comparator<? super T> cmp)`	Sorts the specified range of the specified array of objects according to the order induced by the specified comparator.
`static <T> void parallelSort(T[] a, Comparator<? super T> cmp)`	Sorts the specified array of objects according to the order induced by the specified comparator.

spliterator方法

方法	描述
`static Spliterator.OfDouble spliterator(double[] array)`	将该数组的所有元素转换成对应的`Spliterator`对象。
`static Spliterator.OfDouble spliterator(double[] array, int startInclusive, int endExclusive)`	该方法与上一个方法相似,区别是该方法仅转换`startInclusive`到`endExclusive`索引的元素。
`static Spliterator.OfInt spliterator(int[] array)`	Returns a Spliterator.OfInt covering all of the specified array.
`static Spliterator.OfInt spliterator(int[] array, int startInclusive, int endExclusive)`	Returns a Spliterator.OfInt covering the specified range of the specified array.
`static Spliterator.OfLong spliterator(long[] array)`	Returns a Spliterator.OfLong covering all of the specified array.
`static Spliterator.OfLong spliterator(long[] array, int startInclusive, int endExclusive)`	Returns a Spliterator.OfLong covering the specified range of the specified array.
`static <T> Spliterator<T> spliterator(T[] array)`	Returns a Spliterator covering all of the specified array.
`static <T> Spliterator<T> spliterator(T[] array, int startInclusive, int endExclusive)`	Returns a Spliterator covering the specified range of the specified array.

stream方法

方法	描述
`static DoubleStream stream(double[] array)`	该方法将数组转换为`Stream,Stream`是`Java8`新增的流式编程的`API`。
`static DoubleStream stream(double[] array, int startInclusive, int endExclusive)`	该方法与上一个方法相似,区别是该方法仅将`fromIndex`到`toIndex`索引的元素转换为`Stream`。
`static IntStream stream(int[] array)`	Returns a sequential IntStream with the specified array as its source.
`static IntStream stream(int[] array, int startInclusive, int endExclusive)`	Returns a sequential IntStream with the specified range of the specified array as its source.
`static LongStream stream(long[] array)`	Returns a sequential LongStream with the specified array as its source.
`static LongStream stream(long[] array, int startInclusive, int endExclusive)`	Returns a sequential LongStream with the specified range of the specified array as its source.
`static <T> Stream<T> stream(T[] array)`	Returns a sequential Stream with the specified array as its source.
`static <T> Stream<T> stream(T[] array, int startInclusive, int endExclusive)`	Returns a sequential Stream with the specified range of the specified array as its source.

程序示例 `Arrays`类java8新增方法

下面程序示范了Java8为Arrays类新增的方法:

import java.util.Arrays;
import java.util.function.*;

public class ArraysTest2 {
    public static void main(String[] args) {
        int[] arr1 = new int[] { 3, -4, 25, 16, 30, 18 };
        // 对数组arr1进行并发排序
        Arrays.parallelSort(arr1);
        System.out.println("arr1="+Arrays.toString(arr1));


        int[] arr2 = new int[] { 3, -4, 25, 16, 30, 18 };
        Arrays.parallelPrefix(arr2, new IntBinaryOperator() {
            // left代表数组中前一个所索引处的元素，计算第一个元素时，left为1
            // right代表数组中当前索引处的元素
            public int applyAsInt(int left, int right) {
                return left * right;
            }
        });
        System.out.println("arr2="+Arrays.toString(arr2));


        int[] arr3 = new int[5];
        Arrays.parallelSetAll(arr3, new IntUnaryOperator() {
            // operand代表正在计算的元素索引
            public int applyAsInt(int operand) {
                return operand * 5;
            }       
        });
        System.out.println("arr3="+Arrays.toString(arr3));
    }
}

上面程序中调用了parallelSort()方法对数组执行排序,该方法的功能与传统sort()方法大致相似,只是在多CPU机器上会有更好的性能。

第二段代码使用的计算公式为left*right,其中left代表数组中前一个索引处的元素,right代表数组中当前索引处的元素。程序使用的数组为

1	[-4, 3, 16, 18, 25, 30]

计算新的数组元素的方式为:

1	[13=3,3-4=-12,-1225=-300,-30016=-48000,-4800030=-144000,-14400018=-2592000]

因此将会得到如下新的数组元素:

1	[3, -12, -300, -4800, -144000, -2592000]

第三段代码使用公式operand*5来设置数组元素,该公式中operand代表正在计算的数组元素的索引。因此第三段粗体字代码计算得到的数组为:

1	[0, 5, 10, 15, 20]

4.6.5 Java8增强的工具类 Arrays

程序示例

Java8增强的Arrays方法

binarySearch方法

copyOf方法

copyOfRange方法

fill方法

sort方法

equals方法

toString方法

程序示例 Arrays类Java8新增方法

System类的arrayCopy复制数组

java8新增方法

parallelPrefix方法

setAll方法

parallelSetAll方法

parallelSort方法

spliterator方法

stream方法

程序示例 Arrays类java8新增方法

程序示例 `Arrays`类java8新增方法