In Java, multidimensional arrays are actually arrays of arrays. For example, the following declares a two-dimensional array variable called twoD.
int twoD[][] = new int[4][5];
This allocates a 4-by-5 array and assigns it to twoD. This array will look like the one shown in the following:
[leftIndex][rightIndex]
[0][0] [0][1] [0][2] [0][3] [0][4]
[1][0] [1][1] [1][2] [1][3] [1][4]
[2][0] [2][1] [2][2] [2][3] [2][4]
[3][0] [3][1] [3][2] [3][3] [3][4]
The wrong way to think about multi-dimension arrays
+----+----+----+
| 1| 2| 3|
+----+----+----+
| 4| 5| 6|
+----+----+----+
| 7| 8| 9|
+----+----+----+
right way to think about multi-dimension arrays
+--+ +----+----+----+
| |--------| 1| 2| 3|
+--+ +----+----+----+ +----+----+----+
| |-----------------------------| 4| 5| 6|
+--+ +----+----+----+ +----+----+----+
| |---| 7| 8| 9|
+--+ +----+----+----+
An irregular multi-dimension array
+--+ +----+----+
| |--------| 1| 2|
+--+ +----+----+ +----+----+----+
| |-----------------------------| 4| 5| 6|
+--+ +----+----+----+----+ +----+----+----+
| |---| 7| 8| 9| 10|
+--+ +----+----+----+----+
The following code use nested for loop to assign values to a two-dimensional array.
public class Main {
public static void main(String args[]) {
int twoD[][] = new int[4][5];
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 5; j++) {
twoD[i][j] = i*j;
}
}
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 5; j++) {
System.out.print(twoD[i][j] + " ");
}
System.out.println();
}
}
}
This program generates the following output:
0 0 0 0 0
0 1 2 3 4
0 2 4 6 8
0 3 6 9 12