二维数组内存分布

int arr[][] = new int[2][3];
arr[1][1] = 8;

动态初始化-列数不确定

• 所谓列数不确定，即每个一维数组里所含有的元素的个数不确定

内存分布

1.执行 int arr[][] = new int[3][];

2. 遍历数组并赋值

package Array;

public class TwoDiemantionalArray {
   public static void main(String[] args) {
       int arr[][] = new int[3][];
       for (int i = 0; i < arr.length; i++) {
           arr[i] = new int[i + 1];

           //遍历数组，赋值
           for (int j = 0; j < arr[i].length; j++) {
               arr[i][j] = i + 1;
           }
       }

       //遍历输出
       for (int i = 0; i < arr.length; i++) {
           for (int j = 0; j < arr[i].length; j++){
               System.out.print(arr[i][j] + " ");
           }
           System.out.println();
       }
   }
}

结果：

1
2 2
3 3 3

应用–杨辉三角

package Array;

public class YangHui {
    public static void main(String[] args) {
        int arr[][] = new int[10][];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = new int[i + 1];
            for (int j = 0; j < arr[i].length; j++) {
//                if (i == 0 | j ==0)
//                    arr[i][j] = 1;
//                else if (i == j)
//                    arr[i][j] = 1;
                if (j == 0 | j == arr[i].length - 1)
                    arr[i][j] = 1;
                else
                    arr[i][j] = arr[i - 1][j] + arr[i - 1][j - 1];

                System.out.print(arr[i][j] + "\t");
            }
            System.out.println();
        }
    }
}

结果

1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
1 5 10 10 5 1
1 6 15 20 15 6 1
1 7 21 35 35 21 7 1
1 8 28 56 70 56 28 8 1
1 9 36 84 126 126 84 36 9 1

例题

在数组中插入一个数值，使得数组成按照从小到大的顺序排列

import java.util.Scanner;

public class AsdArray {
    public static void main(String[] args) {
        int arr[] = {10,12,45,90};
        Scanner input = new Scanner(System.in);
//        int addNum = input.nextInt();
        int addNum = 200;
        int index = -1;

        //锁定位置
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] >= addNum) {
                index = i;
                break;
            }
        }
        if (index == -1)
            index = arr.length;

//        System.out.println(index);

		// 扩容
        int arr1[] = new int[arr.length + 1];
        //插入
        arr1[index] = addNum;
        for (int i = 0; i < index; i++) {
            arr1[i] = arr[i];
        }
        for (int i = index + 1; i < arr1.length; i++) {
            arr1[i] = arr[i - 1];
        }
        arr = arr1;

        for (int i:
             arr) {
            System.out.print(i + " ");
        }
    }
}

结果

10 12 45 90 200