방법 1(정식)

int[][] arr;
        arr = new int[2][3];
        arr[0][0] = 1;
        arr[0][1] = 2;
        arr[0][2] = 3;
        arr[1][0] = 4;
        arr[1][1] = 5;
        arr[1][2] = 6;

방법 2

int[][] arr= new int[2][3];
       arr[0][0] = 1;
       arr[0][1] = 2;
       arr[0][2] = 3;
       arr[1][0] = 4;
       arr[1][1] = 5;
       arr[1][2] = 6;

방법 3

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

방법 4

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

오류

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