matrix in java

int[][] matrix1 = new int[2][2];
matrix1[0][0] = 1;
matrix1[0][1] = 2;
matrix1[1][0] = 3;
matrix1[1][1] = 4;

initialize matrix with values in java

int matrix2[][] = { {1,2,3,4},{5,6,7,8},{9,10,11,12} };
or
int[][] matrix3 = { {1,2,3,4},{5,6,7,8},{9,10,11,12} };