Java 数组创建与使用详解

int[] numbers;   // 推荐写法
// 或
int numbers[];   // 兼容写法（不推荐）

numbers = new int[5];  // 创建一个长度为5的int数组

int[] numbers = new int[5];

int[] arr = new int[3];

int[] nums = new int[3];
System.out.println(nums[0]);  // 输出 0

int[] scores = {90, 85, 100, 70};
String[] names = {"Alice", "Bob", "Charlie"};

int[] ages = new int[3];
ages[0] = 18;
ages[1] = 20;
ages[2] = 22;

int[] arr = {10, 20, 30};
System.out.println(arr[0]);  // 输出 10
System.out.println(arr[2]);  // 输出 30

int[] arr = new int[3];
arr[3] = 100;  // ❌ 错误：最大索引是 2

int[] data = {1, 2, 3, 4};
System.out.println(data.length); // 输出 4

int[] nums = {10, 20, 30, 40};
for (int i = 0; i < nums.length; i++) {
    System.out.println("索引 " + i + " 的值是 " + nums[i]);
}

for (int num : nums) {
    System.out.println(num);
}

int[][] matrix = new int[2][3];  // 2行3列

int[][] matrix = {
    {1, 2, 3},
    {4, 5, 6}
};

System.out.println(matrix[0][2]); // 输出 3

for (int i = 0; i < matrix.length; i++) {
    for (int j = 0; j < matrix[i].length; j++) {
        System.out.print(matrix[i][j] + " ");
    }
    System.out.println();
}

1 2 3
4 5 6

int[][] jagged = new int[3][];
jagged[0] = new int[2];
jagged[1] = new int[4];
jagged[2] = new int[1];

import java.util.Arrays;
public class ArrayDemo {
    public static void main(String[] args) {
        int[] nums = {5, 2, 9, 1};
        Arrays.sort(nums);              // 排序
        System.out.println(Arrays.toString(nums)); // 输出 [1, 2, 5, 9]
        int index = Arrays.binarySearch(nums, 5);  // 二分查找
        System.out.println("5 的索引是：" + index);
        int[] copy = Arrays.copyOf(nums, nums.length); // 复制数组
        System.out.println(Arrays.equals(nums, copy)); // true
    }
}