在Java 8中，您可以使用类似于以下内容的东西。

String[] strs = IntStream.range(0, 15)  // 15 is the size
    .mapToObj(i -> Integer.toString(i))
    .toArray(String[]::new);

以原始数据类型int为例，有几种声明int数组的方法：

int[] i = new int[capacity];
int[] i = new int[] {value1, value2, value3, etc};
int[] i = {value1, value2, value3, etc};

在这些情况下，你可以使用 int i[] 替代 int[] i。

使用反射，你可以使用 (Type[]) Array.newInstance(Type.class, capacity);

请注意，在方法参数中，... 表示可变参数。实际上，任何数量的参数都可以。以下代码更容易理解:

public static void varargs(int fixed1, String fixed2, int... varargs) {...}
...
varargs(0, "", 100); // fixed1 = 0, fixed2 = "", varargs = {100}
varargs(0, "", 100, 200); // fixed1 = 0, fixed2 = "", varargs = {100, 200};

多维数组

多维数组更难处理。实际上，一个二维数组就是一个数组的数组。int[][] 表示 int[] 的数组。关键在于如果一个 int[][] 被声明为 int[x][y]，最大的索引是 i[x-1][y-1]。实质上，一个矩形的 int[3][5] 是：

[0, 0] [1, 0] [2, 0]
[0, 1] [1, 1] [2, 1]
[0, 2] [1, 2] [2, 2]
[0, 3] [1, 3] [2, 3]
[0, 4] [1, 4] [2, 4]

int size = 3;
int[] intArray = (int[]) Array.newInstance(int.class, size ); 

声明一个对象引用的数组:

class Animal {}

class Horse extends Animal {
    public static void main(String[] args) {

        /*
         * Array of Animal can hold Animal and Horse (all subtypes of Animal allowed)
         */
        Animal[] a1 = new Animal[10];
        a1[0] = new Animal();
        a1[1] = new Horse();

        /*
         * Array of Animal can hold Animal and Horse and all subtype of Horse
         */
        Animal[] a2 = new Horse[10];
        a2[0] = new Animal();
        a2[1] = new Horse();

        /*
         * Array of Horse can hold only Horse and its subtype (if any) and not
           allowed supertype of Horse nor other subtype of Animal.
         */
        Horse[] h1 = new Horse[10];
        h1[0] = new Animal(); // Not allowed
        h1[1] = new Horse();

        /*
         * This can not be declared.
         */
        Horse[] h2 = new Animal[10]; // Not allowed
    }
}

数组是一串项目的有序列表。

int item = value;

int [] one_dimensional_array = { value, value, value, .., value };

int [][] two_dimensional_array =
{
  { value, value, value, .. value },
  { value, value, value, .. value },
    ..     ..     ..        ..
  { value, value, value, .. value }
};

Object item = new Object();

Object [] one_dimensional_array = { new Object(), new Object(), .. new Object() };

Object [][] two_dimensional_array =
{
  { new Object(), new Object(), .. new Object() },
  { new Object(), new Object(), .. new Object() },
    ..            ..               ..
  { new Object(), new Object(), .. new Object() }
};

对于对象而言，您需要将其指定为null，或使用new Type（...）初始化它们，类似String和Integer的类是特殊情况，将按以下方式处理。

String [] a = { "hello", "world" };
// is equivalent to
String [] a = { new String({'h','e','l','l','o'}), new String({'w','o','r','l','d'}) };

Integer [] b = { 1234, 5678 };
// is equivalent to
Integer [] b = { new Integer(1234), new Integer(5678) };

一般情况下，您可以创建 M 维的数组。

int [][]..[] array =
//  ^ M times [] brackets

    {{..{
//  ^ M times { bracket

//            this is array[0][0]..[0]
//                         ^ M times [0]

    }}..}
//  ^ M times } bracket
;

值得注意的是，创建一个 M 维数组在空间方面是昂贵的。因为当你创建一个每个维度上都有 N 的 M 维数组时，数组的总大小比 N^M 还要大，因为每个数组都有一个引用，在 M 维中存在一个 (M-1) 维的引用数组。总大小如下所示：

Space = N^M + N^(M-1) + N^(M-2) + .. + N^0
//      ^                              ^ array reference
//      ^ actual data

声明

一维数组

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

一维数组

包含默认值

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

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

通过数组字面量

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()};

使用for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
}

使用 for 和 Random 循环

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 Stream（自Java 8以来）

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 Java 8 的 Random 和 Stream

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

多维数组

带默认值

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

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

使用数组字面量

int[][] nums1 = {
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
};
int[][] nums2 = new int[][]{
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
};

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

使用for循环

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

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

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

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

这个很简单和直接创建一个 List。（List 和 Array 之间的区别是什么？）现在如果你真的想要一个 Array，你仍然可以使用：

String[] numberArray = Arrays.asList("1", "2", "3").toArray(new String[0]);

声明并初始化Java 8及更高版本。创建一个简单的整数数组：

int [] a1 = IntStream.range(1, 20).toArray();
System.out.println(Arrays.toString(a1));
// Output: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

int [] a2 = new Random().ints(15, -50, 50).toArray();
double [] a3 = new Random().doubles(5, 0, 1e17).toArray();

幂次数序列：

double [] a4 = LongStream.range(0, 7).mapToDouble(i -> Math.pow(2, i)).toArray();
System.out.println(Arrays.toString(a4));
// Output: [1.0, 2.0, 4.0, 8.0, 16.0, 32.0, 64.0]

对于 String[]，您必须指定一个构造函数：

String [] a5 = Stream.generate(()->"I will not squeak chalk").limit(5).toArray(String[]::new);
System.out.println(Arrays.toString(a5));

String [][] a6 = List.of(new String[]{"a", "b", "c"} , new String[]{"d", "e", "f", "g"})
    .toArray(new String[0][]);
System.out.println(Arrays.deepToString(a6));
// Output: [[a, b, c], [d, e, f, g]]

要创建类对象的数组，您可以使用 java.util.ArrayList 来定义一个数组：

public ArrayList<ClassName> arrayName;
arrayName = new ArrayList<ClassName>();

arrayName.add(new ClassName(class parameters go here);

从数组中读取：

ClassName variableName = arrayName.get(index);

//repeats for every value in the array
for (ClassName variableName : arrayName){
}
//Note that using this for loop prevents you from editing arrayName

允许您编辑arrayName的for循环（传统的for循环）：

for (int i = 0; i < arrayName.size(); i++){
    //manipulate array here
}

这里有很多答案。我添加了一些创建数组的巧妙方法（从考试角度来看，了解这个是很好的）。

1. Declare and define an array

   int intArray[] = new int[3];
   

   This will create an array of length 3. As it holds a primitive type, int, all values are set to 0 by default. For example,

   intArray[2]; // Will return 0
   

2. Using box brackets [] before the variable name

   int[] intArray = new int[3];
   intArray[0] = 1;  // Array content is now {1, 0, 0}
   

3. Initialise and provide data to the array

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

   This time there isn't any need to mention the size in the box bracket. Even a simple variant of this is:

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

4. An array of length 0

   int[] intArray = new int[0];
   int length = intArray.length; // Will return length 0
   

   Similar for multi-dimensional arrays

   int intArray[][] = new int[2][3];
   // This will create an array of length 2 and
   //each element contains another array of length 3.
   // { {0,0,0},{0,0,0} }
   int lenght1 = intArray.length; // Will return 2
   int length2 = intArray[0].length; // Will return 3
   

在变量之前使用方括号：

    int[][] intArray = new int[2][3];

如果您在末尾放置一个方括号，也完全没问题：

    int[] intArray [] = new int[2][4];
    int[] intArray[][] = new int[2][3][4]

一些例子

    int [] intArray [] = new int[][] {{1,2,3},{4,5,6}};
    int [] intArray1 [] = new int[][] {new int[] {1,2,3}, new int [] {4,5,6}};
    int [] intArray2 [] = new int[][] {new int[] {1,2,3},{4,5,6}}
    // All the 3 arrays assignments are valid
    // Array looks like {{1,2,3},{4,5,6}}

并非每个内部元素的大小都是强制性的。

    int [][] intArray = new int[2][];
    intArray[0] = {1,2,3};
    intArray[1] = {4,5};
    //array looks like {{1,2,3},{4,5}}

    int[][] intArray = new int[][2] ; // This won't compile. Keep this in mind.

如果您使用上述语法，请确保在正向方向上指定方括号中的值。否则它将无法编译。以下是一些示例：

    int [][][] intArray = new int[1][][];
    int [][][] intArray = new int[1][2][];
    int [][][] intArray = new int[1][2][3];

另一个重要的特性是协变

    Number[] numArray = {1,2,3,4};   // java.lang.Number
    numArray[0] = new Float(1.5f);   // java.lang.Float
    numArray[1] = new Integer(1);    // java.lang.Integer
   // You can store a subclass object in an array that is declared
   // to be of the type of its superclass.
   // Here 'Number' is the superclass for both Float and Integer.

   Number num[] = new Float[5]; // This is also valid

重要提示：对于引用类型，在数组中存储的默认值为null。