Multi-Dimensional Arrays
Sometimes you need to represent a grid, a matrix, or a table. Multi-dimensional arrays let you do that. In Java, a 2D array is essentially an array of arrays.
Declaration and initialization
// 2D array with 3 rows, 4 columns
int[][] matrix = new int[3][4];
// Initialize with values
int[][] grid = {
{1, 2, 3},
{4, 5, 6},
{7, 8, 9}
};
// Accessing elements
int element = grid[1][2]; // 6
Jagged arrays
Rows can have different lengths.
int[][] jagged = new int[3][];
jagged[0] = new int[2];
jagged[1] = new int[3];
jagged[2] = new int[1];
Traversing a 2D array
Use nested loops: row-major order (outer loop for rows, inner for columns).
for (int i = 0; i < matrix.length; i++) {
for (int j = 0; j < matrix[i].length; j++) {
System.out.print(matrix[i][j] + " ");
}
System.out.println();
}
2D arrays are used for matrices, grids, image processing, dynamic programming tables, etc.
Two Minute Drill
- Multi-dimensional arrays are arrays of arrays.
- 2D arrays declared as `type[][] name`.
- Access via `array[row][col]`.
- Jagged arrays allow rows of different lengths.
- Common operations: matrix addition, multiplication, traversal.
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