Two Dimensional Arrays (Array of Arrays)
To inform the compiler that it is a two dimensional array, place two pairs of square braces either as prefix or suffix to array object. We can place any number of one dimensional arrays in a two dimensional array. A C/C++ programmer is much aware of "a two dimensional array is an array of one dimensional arrays", (Array of Arrays).
Creation, Assignment and Accessing two dimensional arrays
Following ArrayTest3 is an example of a two-dimensional array. A marks array object is created and elements are assigned later.
public class ArrayTest3
{
public static void main(String args[])
{
double marks[][] = new double[3][4];
System.out.println("Rows count: " + marks.length);
System.out.println("Elements of 1st row: " + marks[0].length);
System.out.println("Default value: " + marks[0][0]);
// 1st row values
marks[0][0] = 45.9;
marks[0][1] = 55.9;
marks[0][2] = 65.9;
marks[0][3] = 75.9;
// 2nd row values
marks[1][0] = 45.4;
marks[1][1] = 55.4;
marks[1][2] = 65.4;
marks[1][3] = 75.4;
// 3rd row values
marks[2][0] = 45.2;
marks[2][1] = 55.2;
marks[2][2] = 65.2;
marks[2][3] = 75.2;
System.out.println("1st element value: " + marks[0][0]);
System.out.println("\nPrinting in matrix form");
for(int i = 0; i < marks.length; i++)
{
for(int j = 0; j < marks[i].length; j++)
{
System.out.print(marks[i][j] + "\t");
}
System.out.println(); // just to give a new line
}
}
}
double marks[][] = new double[3][4];
The above statement creates a two-dimensional array object marks that can store 12 elements of double data type, matrixed in 3 rows and 4 columns. Being double, the default value assigned for all the 12 elements is 0.0.
Following is the schematic representation of the task of the above program.
- marks.length gives the number of rows present in the two-dimensional array.
- marks[0].length gives the number of elements present in the first row. Ofcourse, it is the same for all the rows; but differs in the later program.
- There is no predefined way to find the total number of elements present in a two-dimensional array.
- marks[0][0] returns the element existing in the first row and first column.
Initialization and Accessing Two Dimensional Arrays (Array of Arrays)
The previous program ArrayTest3 is modified as ArrayTest4 to illustrate two-dimensional array initialization.
public class ArrayTest4
{
public static void main(String args[])
{
double marks[][] = {
{ 41.6, 51.6, 61.6, 71.6 },
{ 42.7, 52.7, 62.7, 72.7 },
{ 43.8, 53.8, 63.8, 73.8 }
};
System.out.println("Rows count: " + marks.length);
System.out.println("1st row element count: " + marks[0].length);
System.out.println("1st element: " + marks[0][0]);
System.out.println("\nMatrix Form Printing");
for(int i = 0; i < marks.length; i++)
{
for(int j = 0; j < marks[i].length; j++)
{
System.out.print(marks[i][j] + "\t");
}
System.out.println();
}
}
}
double marks[][] = {
{ 41.6, 51.6, 61.6, 71.6 },
{ 42.7, 52.7, 62.7, 72.7 },
{ 43.8, 53.8, 63.8, 73.8 }
};
The above code clearly indicates that two dimensional array is an array of arrays. The marks array contains 3 rows, each row containing 4 elements.
The above code can be modified as follows.
double d1[] = { 41.6, 51.6, 61.6, 71.6 };
double d2[] = { 42.7, 52.7, 62.7, 72.7 };
double d3[] = { 43.8, 53.8, 63.8, 73.8 };
double marks[][] = { d1, d2, d3 };
Three one-dimensional arrays d1, d2 and d3 are placed with marks object.