一、二维数组的定义

public class TwoArrayTest {
    public static void main(String[] args) {
      //二维数组声明与初始化
      //方式1：静态初始化
      int[][] arr = new int[][]{{1,2,3},{1,2,3},{1,2,3}};
      //方式2：动态初始化
      int[][] arr2 = new int[3][3];
      arr2[0][1] = 4;
      //数组元素调用
      System.out.println(arr2[0][1]);
      //数组的长度
        System.out.println(arr2.length);
        System.out.println(arr2[0].length);
      //数组的遍历
        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();
        }
        //数组元素的默认初始化值
        /**
         * 外层元素：默认存储的是地址值
         * 内层元素：默认存储的与一维数组默认值相同
         */
        int[][] arr3 = new int[2][1];
        System.out.println(arr3[0]);//地址值
        System.out.println(arr3[0][0]);//0
    }
}

 二、二维数组练习

2.1、求元素总和 

public class ArrayExer04 {
    public static void main(String[] args) {
        int[][] arr = {{3,5,8},{12,9},{7,0,6,4}};
        //记录元素总和
        int sum = 0;
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) {
                System.out.print(arr[i][j] + "\t");
                sum += arr[i][j];
            }
            System.out.println();
        }
        System.out.println("元素总和为:" + sum);
    }
}