2D Arrays in Java

gradeTable

Student	Week
	0	1	2	3	4
0	99	42	74	83	100
1	90	91	72	88	95
2	88	61	74	89	96
3	61	89	82	98	93
4	93	73	75	78	99
5	50	65	92	87	94
6	43	98	78	56	99

In Java, a table may be implemented as a 2D array. Each slot of the array is a variable that can hold a value and works like any variable. As with one dimensional arrays, every slot in a 2D array is of the same type. The type can be a primitive type or an object reference type.

Important: Each slot of the array is specified with a row and column number, in that order.

Say that gradeTable is a 2D array of int, and that (conceptually, at least) it looks like the table to the right. Then,

gradeTable[ 0 ][ 1 ]     // holds 42
gradeTable[ 3 ][ 4 ]     // holds 93
gradeTable[ 6 ][ 2 ]     // holds 78

The subscripted variables are used in assignment statements and arithmetic expressions just like any variable:

gradeTable[ 0 ][ 1 ] = 33 ;   // puts a 33 into row 0 column 1. 
gradeTable[ 3 ][ 4 ]++ ;      // increments the value at row 3 column 4. 
int value = (gradeTable[ 6 ][ 2 ] + 2) / 2 ;  // puts 40 into value