What Is a 2D Array?

A 2D array is an array whose elements are themselves arrays — a grid of values organized into rows and columns. You can think of it exactly like a spreadsheet or a game board.

This 3×3 grid has 3 rows and 3 columns. The element at row 1, column 2 is 6.

Declaring and Creating 2D Arrays (4.11.A)

Using new

int[][] grid = new int[3][4];  // 3 rows, 4 columns — all zeros

The first number is rows, the second is columns. All elements default to 0 (for int), false (for boolean), or null (for objects).

Using an Initializer List

int[][] scores = {
    {90, 85, 92},
    {78, 88, 95},
    {65, 72, 80}
};

Each inner set of braces is one row. This creates a 3×3 array. Java infers the dimensions from the values.

Accessing and Updating Elements (4.11.B)

Access elements with two indices: arr[row][col]. Row always comes first.

int[][] scores = {
    {90, 85, 92},
    {78, 88, 95},
    {65, 72, 80}
};

System.out.println(scores[0][2]);  // 92  (row 0, col 2)
System.out.println(scores[1][0]);  // 78  (row 1, col 0)
System.out.println(scores[2][1]);  // 72  (row 2, col 1)

scores[1][1] = 99;  // replaces 88 with 99

Getting the Dimensions

int[][] grid = new int[4][6];  // 4 rows, 6 columns

System.out.println(grid.length);     // 4  — number of rows
System.out.println(grid[0].length);  // 6  — number of columns

grid.length gives the number of rows because a 2D array is an array of row-arrays, and length counts how many rows there are. grid[0].length gives the length of row 0, which is the number of columns.

// 3 students (rows), 4 test scores each (columns)
int[][] gradebook = {
    {90, 85, 92, 88},
    {78, 80, 75, 82},
    {95, 91, 98, 94}
};

// Student 2's score on test 3:
System.out.println(gradebook[2][3]);  // 94

Summary

• A 2D array is a grid: rows and columns. Declare as int[][] arr = new int[rows][cols].
• Access with arr[row][col] — row index first, column index second.
• arr.length = number of rows. arr[0].length = number of columns.
• Default values are the same as 1D arrays: 0, false, or null depending on type.
• Initializer list syntax nests inner braces for each row.

int[][] grid = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

int[][] m = {
    {10, 20},
    {30, 40},
    {50, 60}
};
System.out.println(m.length + " " + m[0].length);

int[][] data = new int[3][4];

int[][] grid = new int[4][3];

int[][] arr = {
    {1,  2,  3,  4},
    {5,  6,  7,  8},
    {9, 10, 11, 12}
};
System.out.println(arr[2][1] + arr[0][3]);

int[][] board = new int[3][3];
board[0][0] = 1;
board[1][1] = 2;
board[2][2] = 3;
System.out.println(board[0][1] + board[1][1] + board[2][1]);

int[][] table = {
    {2, 4, 6},
    {8, 10, 12}
};
table[0][1] = table[1][2] - table[0][0];
System.out.println(table[0][1]);