11.二维数组:int[][] arr=new int[2][3],arr[0][1]=21;int[][] arr=new int[2][],int a1={1},a2={2},arr[0]=a1,arr[1]=a2;int[][] arr={{1},{2},{3}}; 12.二维数组遍历:for(int a=0;i<arr.length;i++){for(int j=0j<arr[i].length;j++) {System.out.println(arr...