如何在Java中声明和初始化数组？

如何在Java中声明和初始化数组？

您可以使用数组声明或数组文字（但只有当您立即声明并影响变量时，数组文字才能用于重新分配数组）

对于基本类型：

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

// Since Java 8. Doc of IntStream: https://docs.oracle.com/javase/8/docs/api/java/util/stream/IntStream.html

int [] myIntArray = IntStream.range(0, 100).toArray(); // From 0 to 99
int [] myIntArray = IntStream.rangeClosed(0, 100).toArray(); // From 0 to 100
int [] myIntArray = IntStream.of(12,25,36,85,28,96,47).toArray(); // The order is preserved.
int [] myIntArray = IntStream.of(12,25,36,85,28,96,47).sorted().toArray(); // Sort 

对于类，例如

String

，它是相同的：

String[] myStringArray = new String[3];
String[] myStringArray = {"a", "b", "c"};
String[] myStringArray = new String[]{"a", "b", "c"};

当您先声明数组，然后对其进行初始化、将数组作为函数参数传递或返回数组时，第三种初始化方法非常有用。显式类型是必需的

String[] myStringArray;
myStringArray = new String[]{"a", "b", "c"};

或者

// Either method works
String arrayName[] = new String[10];
String[] arrayName = new String[10];

---

它声明了一个名为

arrayName

的数组，大小为10（可以使用元素0到9）。

可以通过多种方式在Java中声明数组：

float floatArray[]; // Initialize later
int[] integerArray = new int[10];
String[] array = new String[] {"a", "b"};

您可以在网站和中找到更多信息

---

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

如果您了解每个部分，我觉得这很有帮助：

Type[] name = new Type[5];

Type[]

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。数组类型是它们自己的类型，这允许您创建多维数组，如

Type[][

（Type[]的数组类型）。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量。例如，如果Java知道基本类型

type

需要32个字节，并且您想要一个大小为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};

---

这不仅会创建空空间，还会用这些值填充它。Java可以判断原语是整数，并且有5个，因此可以隐式地确定数组的大小。

此外，如果您需要更动态的内容，还可以使用列表接口。这样做效果不好，但更灵活：

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

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

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

List listOfString=new ArrayList（）；
添加（“foo”）；
添加（“条”）；
字符串值=listOfString.get（0）；
资产质量（价值，“foo”）；

以下显示了数组的声明，但数组未初始化：

 int[] myIntArray = new int[3];

---

下面显示了数组的声明和初始化：

int[] myIntArray = {1,2,3};

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

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

ClassName variableName = arrayName.get(index);

现在，下面还显示了数组的声明和初始化：

int[] myIntArray = {1,2,3};

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

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

ClassName variableName = arrayName.get(index);

但是第三个显示了匿名数组对象创建的属性，它是由一个引用变量“myIntArray”指向的，所以如果我们只写“newint[]{1,2,3}”；那么这就是匿名数组对象的创建方式

如果我们只写：

int[] myIntArray;

这不是数组的声明，但以下语句使上述声明完成：

myIntArray=new int[3];

---

有两种类型的数组。

一维阵列 默认值的语法：

int[] num = new int[5];

或（不太受欢迎）

给定值的语法（变量/字段初始化）：

或（不太受欢迎）

注意：为了方便起见，int[]num更可取，因为它清楚地表明您在这里谈论的是数组。否则没有区别。不客气。

多维数组 宣言 或

或

初始化 或

不规则阵列（或非矩形阵列） 因此，我们在这里明确定义列。
另一种方式：

访问： 不规则数组是多维数组。

---

有关说明，请参见位于

的多维数组详细信息。如果要使用反射创建数组，可以执行以下操作：

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

int[][] array2d = new int[x][y]; // "x" and "y" specify the dimensions
int[][] array2d = { {1,2,3 ...}, {4,5,6 ...} ...};

---

以基本类型

int

为例。有几种方法可以声明和

int

数组：

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

在所有这些中，您可以使用

int i[]

而不是

int[]i

通过反射，您可以使用

（Type[]）Array.newInstance（Type.class，capacity）

请注意，在方法参数中，
..
表示
变量参数
。基本上，任何数量的参数都可以。使用代码更容易解释：

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};

在方法内部，
varargs
被视为正常的
int[]
<代码>类型…

只能在方法参数中使用，因此

int。。。i=newint[]{}

将不会编译

请注意，将

int[]

传递给方法（或任何其他

Type[]

）时，不能使用第三种方法。在语句

int[]i=*{a，b，c，d等}

中，编译器假定

{…}

表示

int[]

。但这是因为您正在声明一个变量。将数组传递给方法时，声明必须是

new-Type[capacity]

或

new-Type[]{…}

多维数组 多维数组更难处理。从本质上讲，二维数组是数组的数组

int[][]

表示

int[]

s的数组。关键是如果一个

int[][]

被声明为

int[x][y]

，最大索引是

i[x-1][y-1]

。基本上，矩形

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]

---

声明对象引用数组：

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
    }
}

---

数组是项的顺序列表

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 }
};

如果它是一个物体，那么它就是同一个概念

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，您需要将其分配给

null

以使用

新类型（..）

初始化它们，像

String

和

Integer

这样的类是特殊情况，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) };

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

通常，您可以创建

M

维数组

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

M

维数组在空间上非常昂贵。因为当您在所有维度上创建一个

M

维度数组且

N

，数组的总大小大于

N^M

，因为每个数组都有一个引用

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
    }
}

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() }
};

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) };

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

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

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

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

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

int[] array = new int[n]; // "n" being the number of spaces to allocate in the array

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

int[][] array2d = new int[x][y]; // "x" and "y" specify the dimensions
int[][] array2d = { {1,2,3 ...}, {4,5,6 ...} ...};

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

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

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

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

private List<String> list = new ArrayList<String>(){{
    add("e1");
    add("e2");
}};

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();

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]

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]]

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]

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

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

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

int[] values = { 1, 2, 3 }

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

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

int intArray[] = new int[3];

intArray[2]; // Will return 0

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

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

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

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

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

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

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

    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}}

    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.

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

    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

int[] a = new int[5];

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

datatype[] arrayname = new datatype[requiredarraysize];

String[] a = {"as", "asd", "ssd"};

char[] a = {'a', 's', 'w'};

double[] a = {1.2, 1.3, 12.3};

type var-name[];
OR
type[] var-name;

var-name = new type [size];

int intArray[];  // Declaring an array
intArray = new int[20];  // Allocating memory to the array

// The below line is equal to line1 + line2
int[] intArray = new int[20]; // Combining both statements in one
int[] intArray = new int[]{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

// Accessing the elements of the specified array
for (int i = 0; i < intArray.length; i++)
    System.out.println("Element at index " + i + ": "+ intArray[i]);

int[] x = new int[enter the size of array here];

int[] x = new int[10];
              

int[] x = {enter the elements of array here];

int[] x = {10, 65, 40, 5, 48, 31};

public class A {

    public static void main(String[] args) {

        class Movie {

            String movieName;
            String genre;
            String movieType;
            String year;
            String ageRating;
            String rating;

            public Movie(String [] str)
            {
                this.movieName = str[0];
                this.genre = str[1];
                this.movieType = str[2];
                this.year = str[3];
                this.ageRating = str[4];
                this.rating = str[5];
            }
        }

        String [] movieDetailArr = {"Inception", "Thriller", "MovieType", "2010", "13+", "10/10"};

        Movie mv = new Movie(movieDetailArr);

        System.out.println("Movie Name: "+ mv.movieName);
        System.out.println("Movie genre: "+ mv.genre);
        System.out.println("Movie type: "+ mv.movieType);
        System.out.println("Movie year: "+ mv.year);
        System.out.println("Movie age : "+ mv.ageRating);
        System.out.println("Movie  rating: "+ mv.rating);
    }
}

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));

    }
}