和老师上课的案例相似，不过是自己练习看完课重新敲的。
数组的累加求和
package lianxi1;


public class dlshuzuleijiaqiuhe {
public static void main(String[] args) {
int[]arr1={2,3,4};
int[]arr2={7,3,8};
int[]arr3={5,6,7};
int[]arr4={7,8,9};
/* //动态初始化一个二维数组
        int[][] maxarr=new int[4][];
        //把四个一维数组放到一个二维数组中去
        maxarr[0]=arr1;
        maxarr[1]=arr2;
        maxarr[2]=arr3;
        maxarr[3]=arr4;*/

       //静态初始化
        int[][] maxarr=new int[][]{{2,3,4},{7,3,8},{5,6,7},{7,8,9}};
//  遍历数组求和
        int sum=0;
for (int i = 0; i < maxarr.length; i++) {
for (int j = 0; j < maxarr[i].length; j++) {
                sum+=maxarr[i][j];
            }

        }
        System.out.println("数组最终求和答案"+sum);
    }

package lianxi1;

public class shuzulianxi1224 {
public static void main(String[] args) {
int[][] arr = new int[][]{{20, 30}, {5, 3}, {20, 100, 200, 300}};
/*
        System.out.println(arr[0][0]);
        System.out.println(arr[0][1]);
        System.out.println(arr[1][0]);
        System.out.println(arr[1][1]);
        System.out.println(arr[2][0]);
        System.out.println(arr[2][1]);
        System.out.println(arr[2][2]);
        System.out.println(arr[2][3]);
        */
       // 遍历二维数组
        for (int i = 0; i <arr.length ; i++) {
//System.out.println(arr[i]);//地址值
            for (int j = 0; j <arr[i].length ; j++) {
                System.out.println(arr[i][j]);

            }
        }

    }
}

}

package lianxi1;

public class lianxi11 {
public static void main(String[] args) {
int[] arr = {20, 30, 40};
int[] arr2 = {2, 3, 4, 5, 6, 7};
        System.out.println(arr[0]);
        System.out.println(arr2[0]);

int[][] maxArr = new int[2][];
        System.out.println(maxArr[0]);
        System.out.println(maxArr[1]);

int[][] maxArr2 = new int[2][2];
        System.out.println(maxArr2[0][0]);
        System.out.println(maxArr2[0][1]);
        System.out.println(maxArr2[1][0]);
        System.out.println(maxArr2[1][1]);

int num = maxArr2[0][0];
        System.out.println(num);//0

        int[][] arr4 = new int[2][3];
        System.out.println(arr4);
int[] arr3 = {2, 3, 5, 6, 7, 8};
        System.out.println(arr3);//地址值
        System.out.println(arr3[3]);//6
    }
}