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

此外，如果您需要更动态的内容，可以使用List界面。这不会表现得很好，但更灵活：

List<String> listOfString = new ArrayList<String>();

listOfString.add("foo");
listOfString.add("bar");

String value = listOfString.get(0);
assertEquals( value, "foo" );

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。

Type[] variableName = new Type[capacity];

Type[] variableName = {comma-delimited values};



Type variableName[] = new Type[capacity]; 

Type variableName[] = {comma-delimited values};

也是有效的，但我更喜欢在类型后面加括号，因为更容易看出变量的类型实际上是一个数组。

声明数组：int[]arr；

初始化数组：int[]arr=new int[10]；10表示数组中允许的元素数

声明多维数组：int[][]arr；

初始化多维数组：int[][]arr=new int[10][17]；10行17列和170个元素，因为10乘以17等于170。

初始化数组意味着指定数组的大小。

为Java 8和更高版本声明和初始化。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]

为[-50，50]之间的整数和双[0，1E17]创建随机数组：

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

两个序列的功率：

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[]，必须指定构造函数：

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

多维数组：

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]]