- An array is a collection of similar data types that share a common name.
- Arrays of any type can be created and may have one or more dimensions.
- Array elements can be accessed by its index.
- Array index always starts with 0
- It can be divided into two categories:
- One-dimensional Array
- Multi-dimensional Array
One-Dimensional Arrays
- An array with a single sub script is referred as one-dimensional array.
- The general form of a one-dimensional array declaration is:
<data_type> <var-name>[];
int num[];
- Declare a variable of the desired data type.
- Allocate memory that will hold the array, using new, and assign it to the array variable.
class arrayDemo
{
public static void main(String args[])
{
int num[ ];
num= new int[3];
num[0]=10;
num[1]=20;
num[2]=30;
System.out.println (“Value at index 1 is ” + num[1]);
}
}
- We can also combine the declaration of the array variable and memory allocation process in a single statement as shown below:
int num[ ]=new int[3];
- Arrays can also be initialized at the time of declaration using comma-separated list of expressions surrounded by curly braces.
- The comma separates the values of the array elements.
- It will automatically create an array with the size large enough to hold the number of elements specified in the array initialize list.
- There is no need to use new.
Class AutoArray
{
public static void main (String args[ ])
{
int month_days[]={31,28,31,30,31,30,31,31,30,31,30,31};
System.out.println(“April has” + month_days[3] + “days.”);
}
}
Multi-Dimensional Arrays:
- Multidimensional arrays are actually arrays of arrays.
- An array having two or more sub-script is known as multi-dimesional array
- We can specify additional index subscript using another set of square brackets to declare a multidimensional array.
- For example, following statement declares two dimensional array:
int twoD[][] = new int [4] [5];
int threeD[][] = new int[3][4][5];
- The first statement declares array matrix with 4 rows and 5 columns
- The second statement declares 3-D array of matrix with 4 rows and 5 columns
Alternative Array Declaration
- There is an alternative form to declare an array:
<data_type> [ ] <var_name>;
- The square brackets follow the type specifier, and not the name of the array variable.
- For example, the following two declarations are equivalent:
int num[ ] = new int[4]; OR int [ ] num = new int[4];
- This declaration form can be helpful while declaring several arrays at the same time. For example,
int [ ] num1, num2, num3;