Multidimensional Arrays in Java
Vidhu S. Kapadia
The Basic Definitions
• What is an Array?
• An array is a fixed size sequential collection of elements of
identical types.
• They are created with either a new operator or array initializes
• The storage space for arrays is allocated from the garbagecollected heap.
• The element in an array are indexed by the integers 0 to n- 1,
where n is the size of the array
Declaring an Array
• Using the new operator
 new Type [ ]
Here the size of the array must be specified, and all the elements in the
array are initialized to the default initial values based on the types of
elements.
int ia1 = new int [3];
//creates an integer array of size 3; all elements are initialized to 0
Point pa [ ] = new Point [10];
//creates an array of points of size 10; all elements are initialized to
null
Declaring an Array
• Using the one-dimensional array initializer
{v0, v1, …..,vn-1}
The values for v0, v1, …..,vn-1 are the initial values of the
elements in the array. The size of the array is determined by the
number of initial values provided in the array initializer
Int ia2 [ ] = {1, 2, 3};
// Creates an array of size 3; elements are initialized to 1, 2, and 3
respectively
What are Multidimensional
Arrays
• A multidimensional array is treated as an
array of arrays.
– Let a be a k-dimensional array; the elements of a can
be accessed using the following syntax:
a [ i1 ] [ i2 ]…[ ik ]
where n1, n2, ….., nk
Multidimensional Arrays
• Applying what we learned about simple
arrays to multidimensional array, we get the
following:
A k-dimensional array can be created with
either of the following methods:
– Using the new operator
– Using the k-dimensional initializer
Creating k-dimensional Array
Using the new operator
• Using k-dimensional array
initializer
new Type [ n1] [n2]…[nk]
•
Size of each dimension is n1,
n2, …,nk, respectively.
•
All the elements in the array are
initialized to default initial values
based on the type of the
elements
•
{I1, I2, ...., Ik}
where each I1, I2, ...., Ik
is a
(k-1)- dimensional array initializer.
Examples…
•
Using the new operator, the following
example is of creating and initializing
a two-dimensional array.
double mat1[ ][ ] = new double[4][5];
This creates a 4 x 5 two-dimensional
array. All elements are initialized to
0.0.
•
Using k-dimensional array initializer,
the following example is of creating
and initializing a two-dimensional
array.
int mat2[ ] [ ] = {{1, 2, 3}, {4, 5, 6}};
This creates a 2 x 3 twodimensional array. The elements
are initialized as:
mat2[0][0]=1
mat2[0][1]=2
mat2[0][2]=3
mat2[1][0]= 4
mat2[1][1]= 5
mat2[1][2]= 6
Illustrating Two-Dimensional
Array
Processing Multidimensional
Arrays
•
Multidimensional arrays are often processed using for statements.
To process all the items in a two-dimensional array, a for statement
needs to be nested inside another.
int[ ][ ] A = new int[3][4];
The following loop stores 0 into each location in two dimensional array
A:
for (int row = 0; row < 3; row++)
{
for (int column = 0; column < 4; column++)
{
A [row][column] = 0;
}
}
An Example:
• Using a mathematical function in the Java
Math class and handling of two–dimensional
arrays, the following example calculates the
max – min value.
public class MaxMin{
public static void main(String[]args)
{
double mat[ ] [ ]= { {2.3, 5.1, 9.9},
{8.3, 4.5, 7.7},
{ 5.2, 6.1, 2.8}}
int n = mat.length;
int m= mat[0].length;
double maxmin = 0.0;

Running the program
for (int j = 0; j < m; j++){
produces the following
double min = mat[j][0];
result:
for (int i = 1; I <n ; i ++){
The max-min value is 4.5
min = Math.min(min,mat[i][j]);
}
if (j==0){
maxmin = min;
}else{
maxmin = Math.max(maxmin, min);
}
}
System.out.println(“The max-min value is” + maxmin);
}
}
Keep in mind that…
• Computer memory is linear –
• In accessing a multidimensional array you are really
accessing a one-dimensional array in memory.
• You can simulate multidimensional arrays by packing
them into a one-dimensional array.
• The two manners of packing the one-dimensional array
are row-major order, where the array is filled one row at
a time; and column-major order, where columns are
placed into the array.
Interesting Tidbits about Arrays
in Java
• One of the main differences between the arrays in Java
and those in C/C++ is that the Java arrays are ALWAYS
bounds-checked at run time.
• Array bound-checking will automatically detect a major
source of faults in programs, that is exceeding the bounds
of arrays while accessing or manipulating their elements.
• There is no limit on the number of dimensions that an
array type can have. However, arrays of dimension three
or higher are fairly uncommon.
References
• Jia, Xiaoping. Object Oriented Software Development using
Java- 2nd edition, Adison Wesley 2003
• The historical collection classes – Arrays, IBM. April, 16,
2006, http://www-128.ibm.com/developerworks/java/library/jarrays/
• Array initialization, The Code Guru. April, 16, 2006,
http://codeguru.earthweb.com/java/tij/tij0053.shtml