如何在Java中声明和初始化数组？

当前回答

如果“array”是指使用java.util.Arrays，那么可以使用：

List<String> number = Arrays.asList("1", "2", "3");

// Out: ["1", "2", "3"]

这个非常简单明了。

2018-11-14 19:59:02

其他回答

我发现，如果您了解每个部分，这会很有帮助：

Type[] name = new Type[5];

类型[]是名为name的变量的类型（“name”称为标识符）。文字“Type”是基类型，括号表示这是该基的数组类型。数组类型又是它们自己的类型，这允许您创建像类型[][]（类型[]的数组类型）这样的多维数组。关键字new表示为新数组分配内存。括号之间的数字表示新阵列的大小以及要分配的内存。例如，如果Java知道基本类型type需要32个字节，并且您需要一个大小为5的数组，那么它需要在内部分配32*5=160个字节。

您还可以使用已经存在的值创建数组，例如

int[] name = {1, 2, 3, 4, 5};

这不仅创建了空白空间，而且用这些值填充了空白空间。Java可以判断基元是整数，并且有5个基元，因此可以隐式地确定数组的大小。

2009-07-29 14:29:56

package com.examplehub.basics;

import java.util.Arrays;

public class Array {

    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};

        /*
         * numbers[0] = 1
         * numbers[1] = 2
         * numbers[2] = 3
         * numbers[3] = 4
         * numbers[4] = 5
         */
        System.out.println("numbers[0] = " + numbers[0]);
        System.out.println("numbers[1] = " + numbers[1]);
        System.out.println("numbers[2] = " + numbers[2]);
        System.out.println("numbers[3] = " + numbers[3]);
        System.out.println("numbers[4] = " + numbers[4]);

        /*
         * Array index is out of bounds
         */
        //System.out.println(numbers[-1]);
        //System.out.println(numbers[5]);


        /*
         * numbers[0] = 1
         * numbers[1] = 2
         * numbers[2] = 3
         * numbers[3] = 4
         * numbers[4] = 5
         */
        for (int i = 0; i < 5; i++) {
            System.out.println("numbers[" + i + "] = " + numbers[i]);
        }

        /*
         * Length of numbers = 5
         */
        System.out.println("length of numbers = " + numbers.length);

        /*
         * numbers[0] = 1
         * numbers[1] = 2
         * numbers[2] = 3
         * numbers[3] = 4
         * numbers[4] = 5
         */
        for (int i = 0; i < numbers.length; i++) {
            System.out.println("numbers[" + i + "] = " + numbers[i]);
        }

        /*
         * numbers[4] = 5
         * numbers[3] = 4
         * numbers[2] = 3
         * numbers[1] = 2
         * numbers[0] = 1
         */
        for (int i = numbers.length - 1; i >= 0; i--) {
            System.out.println("numbers[" + i + "] = " + numbers[i]);
        }

        /*
         * 12345
         */
        for (int number : numbers) {
            System.out.print(number);
        }
        System.out.println();

        /*
         * [1, 2, 3, 4, 5]
         */
        System.out.println(Arrays.toString(numbers));



        String[] company = {"Google", "Facebook", "Amazon", "Microsoft"};

        /*
         * company[0] = Google
         * company[1] = Facebook
         * company[2] = Amazon
         * company[3] = Microsoft
         */
        for (int i = 0; i < company.length; i++) {
            System.out.println("company[" + i + "] = " + company[i]);
        }

        /*
         * Google
         * Facebook
         * Amazon
         * Microsoft
         */
        for (String c : company) {
            System.out.println(c);
        }

        /*
         * [Google, Facebook, Amazon, Microsoft]
         */
        System.out.println(Arrays.toString(company));

        int[][] twoDimensionalNumbers = {
                {1, 2, 3},
                {4, 5, 6, 7},
                {8, 9},
                {10, 11, 12, 13, 14, 15}
        };

        /*
         * total rows  = 4
         */
        System.out.println("total rows  = " + twoDimensionalNumbers.length);

        /*
         * row 0 length = 3
         * row 1 length = 4
         * row 2 length = 2
         * row 3 length = 6
         */
        for (int i = 0; i < twoDimensionalNumbers.length; i++) {
            System.out.println("row " + i + " length = " + twoDimensionalNumbers[i].length);
        }

        /*
         * row 0 = 1 2 3
         * row 1 = 4 5 6 7
         * row 2 = 8 9
         * row 3 = 10 11 12 13 14 15
         */
        for (int i = 0; i < twoDimensionalNumbers.length; i++) {
            System.out.print("row " + i + " = ");
            for (int j = 0; j < twoDimensionalNumbers[i].length; j++) {
                System.out.print(twoDimensionalNumbers[i][j] + " ");
            }
            System.out.println();
        }

        /*
         * row 0 = [1, 2, 3]
         * row 1 = [4, 5, 6, 7]
         * row 2 = [8, 9]
         * row 3 = [10, 11, 12, 13, 14, 15]
         */
        for (int i = 0; i < twoDimensionalNumbers.length; i++) {
            System.out.println("row " + i + " = " + Arrays.toString(twoDimensionalNumbers[i]));
        }

        /*
         * 1 2 3
         * 4 5 6 7
         * 8 9
         * 10 11 12 13 14 15
         */
        for (int[] ints : twoDimensionalNumbers) {
            for (int num : ints) {
                System.out.print(num + " ");
            }
            System.out.println();
        }

        /*
         * [1, 2, 3]
         * [4, 5, 6, 7]
         * [8, 9]
         * [10, 11, 12, 13, 14, 15]
         */
        for (int[] ints : twoDimensionalNumbers) {
            System.out.println(Arrays.toString(ints));
        }


        int length = 5;
        int[] array = new int[length];
        for (int i = 0; i < 5; i++) {
            array[i] = i + 1;
        }

        /*
         * [1, 2, 3, 4, 5]
         */
        System.out.println(Arrays.toString(array));

    }
}

来源于examplehub/java

2020-10-05 01:55:35

在Java 9中

使用不同的IntStream.iterate和IntStream.takeWhile方法：

int[] a = IntStream.iterate(10, x -> x <= 100, x -> x + 10).toArray();

Out: [10, 20, 30, 40, 50, 60, 70, 80, 90, 100]


int[] b = IntStream.iterate(0, x -> x + 1).takeWhile(x -> x < 10).toArray();

Out: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

在Java 10中

使用局部变量类型推断：

var letters = new String[]{"A", "B", "C"};

2018-02-21 12:45:00

公告

一维阵列

int[] nums1; // best practice
int []nums2;
int nums3[];

多维数组

int[][] nums1; // best practice
int [][]nums2;
int[] []nums3;
int[] nums4[];
int nums5[][];

声明和初始化

一维阵列

使用默认值

int[] nums = new int[3]; // [0, 0, 0]

Object[] objects = new Object[3]; // [null, null, null]

带数组文字

int[] nums1 = {1, 2, 3};
int[] nums2 = new int[]{1, 2, 3};

Object[] objects1 = {new Object(), new Object(), new Object()};
Object[] objects2 = new Object[]{new Object(), new Object(), new Object()};

带有循环

int[] nums = new int[3];
for (int i = 0; i < nums.length; i++) {
    nums[i] = i; // can contain any YOUR filling strategy
}

Object[] objects = new Object[3];
for (int i = 0; i < objects.length; i++) {
    objects[i] = new Object(); // can contain any YOUR filling strategy
}

带循环for和Random

int[] nums = new int[10];
Random random = new Random();
for (int i = 0; i < nums.length; i++) {
    nums[i] = random.nextInt(10); // random int from 0 to 9
}

使用流（从Java 8开始）

int[] nums1 = IntStream.range(0, 3)
                       .toArray(); // [0, 1, 2]
int[] nums2 = IntStream.rangeClosed(0, 3)
                       .toArray(); // [0, 1, 2, 3]
int[] nums3 = IntStream.of(10, 11, 12, 13)
                       .toArray(); // [10, 11, 12, 13]
int[] nums4 = IntStream.of(12, 11, 13, 10)
                       .sorted()
                       .toArray(); // [10, 11, 12, 13]
int[] nums5 = IntStream.iterate(0, x -> x <= 3, x -> x + 1)
                       .toArray(); // [0, 1, 2, 3]
int[] nums6 = IntStream.iterate(0, x -> x + 1)
                       .takeWhile(x -> x < 3)
                       .toArray(); // [0, 1, 2]

int size = 3;
Object[] objects1 = IntStream.range(0, size)
        .mapToObj(i -> new Object()) // can contain any YOUR filling strategy
        .toArray(Object[]::new);

Object[] objects2 = Stream.generate(() -> new Object()) // can contain any YOUR filling strategy
        .limit(size)
        .toArray(Object[]::new);

使用Random和Stream（从Java 8开始）

int size = 3;
int randomNumberOrigin = -10;
int randomNumberBound = 10
int[] nums = new Random().ints(size, randomNumberOrigin, randomNumberBound).toArray();