Arrays in Java

 

One Dimensional Array

An array is an object that can be used to store a list of values. It is made out of a contiguous block of memory that is divided into a number of "Memory Blocks." Each Memory Block can hold a value, and all of the values are of the same type. The Memory Blocks are indexed 0 through SIZE -1 and each Memory Block can be accessed by using its index.

To create an array, you need to perform two steps:

1. declare an array:

Syntax:

              Type arrayname [ ];

2. Create an array using 'new' keyword (Allocate space for its elements):

Syntax:

              arrayname = new Type[ Size ];

Above steps can be combined as follows

               Type arrayname = new Type[ Size];

Where Type may be any data type or reference Type (class name).

Ex:

Assume n = 5

int a[ ];

a = new int[n];

      

    Or

int a[ ] = new int[n];

Memory Map:

Initialization of 1-D array:

           Type arrayname[  ] = { value1,value2,value3,........value n };

           Ex: int a[] = {10,20,30,40,50}; 

Two Dimensional Array

In addition to one dimensional we can create arrays of two or more dimensions. In Java, Multidimensional array are implemented as arrays of arrays. You need to perform two steps to work with multidimensional arrays: 1. Declare the array and 2. Allocate space for its elements. When constructing a two-dimensional array, you specify how many rows and columns you need:

         Type arrayname [  ] [  ];

         arrayname = new Type [M][N];

        Where M = no of rows                        N= no of columns..

Above two steps can be combined as follows

          Type arrayname [ ][ ] = new Type[ M][N];

Ex:

     int a[][];

     a = new int [M][N];

OR

       int a[   ][  ] = new int[ M ][N];

       float a[ ][ ] = new float[2][2];

Here a is two dimensional array having 2 rows and 2 columns. i.e. size is 4, we can store 4 elements in that array.