如何在Java中声明和初始化数组？
当前回答
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();
多维数组
使用默认值
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]]
带数组文字
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()}
};
带有循环
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
}
}
其他回答
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();
多维数组
使用默认值
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]]
带数组文字
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()}
};
带有循环
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
}
}
制作阵列有两种主要方法：
对于空数组：
int[] array = new int[n]; // "n" being the number of spaces to allocate in the array
对于一个初始化的数组：
int[] array = {1,2,3,4 ...};
您还可以创建多维数组，如下所示：
int[][] array2d = new int[x][y]; // "x" and "y" specify the dimensions
int[][] array2d = { {1,2,3 ...}, {4,5,6 ...} ...};
另一种声明和初始化ArrayList的方法：
private List<String> list = new ArrayList<String>(){{
add("e1");
add("e2");
}};
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
数组有两种基本类型。
静态数组：固定大小数组（其大小应在开始时声明，以后不能更改）
动态阵列：不考虑大小限制。（Java中不存在纯动态数组。相反，最鼓励使用List。）
要声明Integer、string、float等静态数组，请使用以下声明和初始化语句。
int[]intArray=新int[10]；String[]intArray=新int[10]；float[]intArray=新int[10]；//这里有10个索引，从0到9
要使用动态功能，必须使用列表。。。列表是纯动态数组，不需要在开头声明大小。下面是用Java声明列表的正确方法-
ArrayList<String>myArray=新ArrayList<String>（）；myArray.add（“值1:something”）；myArray.add（“值2:更多”）；
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