Java - Arrays

Array is a collection of same data type variables under one name. Array can be available in following types.

·       One dimensional array

·       Two dimensional array

·       Three or more dimensional array

Ex: int mark[]=new int[5];

     Size               5

     Lowerbound         0

     Upperbound         4

     Element            mark[0],mark[1],….mark[4]

     Array Name         mark

     Subscript          0,1,2,3,4

Array Declaration

One dimensional array

Type 1

datatype variablename[]=new datatype[size];

int n[]=new int[10];

Type 2

datatype[] variablename=new datatype[size];

int[] n=new int[10];

Type 3

datatype variablename[]={value….};

int n[]={1,2,3,4};

String name[]={“java”,”j2ee”};

char ch[]={‘a’,’b’,’c’};

Type 4

datatype variablename[]; // step 1

variablename=new datatype[size]; //step 2

int n[];

n=new int[5];

In type 4 the array can be declared as class scope, then it can be resized within method at more times.

Two dimensional array

Type 1

datatype variablename[][]=new datatype[rowsize][columnsize];

Ex: int a[][]=new int[2][3]; // a has 6 elements (2*3)

Type 2

datatype variablename[][];

variablename=new datatype[rowsize][coulmnsize];

int b[][];

b=new int[2][3];

Type 3

datatype variablename[][]={{values},{values}};

int a[][]={{1,2,3},{1,2,3}};

Three dimensional array

Type 1

int a[][][]=new int[2][2][2];

Type 2

int a[][][];

a=new int[2][2][2];

Four dimensional array

Type 1

int a[][][][]=new int[2][2][2][3];

Type 2

int a[][][][];

a=new int[2][2][2][3];

Jagged arrays

Two or more dimensional can be declared as jagged arrays to allocate memory at run time.

Runtime memory allocation

Ex 1

int a[][]=new int[5][];

a[0]=new int[3];

a[1]=new int[10];

It means a[0] has 3 columns, a[1] has 10 columns.

Ex 2

int a[][][]=new int[2][][];

a[0]=new int[2][3];

a[1]=new int[3][4];

It means a[0] has 2*3 array, a[1] has 3*4 array

Assigning arrays

Arrays can be assigned in java. Consider following syntaxes.

Ex 1

int a[]=new int[2];

int b=a[0]; // One value assign

Ex 2

int a[][]=new int[2][2];

int b[]=a[0];  // One dim assign

int c[]=a[1]; // One dim assign

Ex 3

int a[][][]=new int[2][2][3];

int b[][][]=a; // Three dim assign

int c[][]=a[0]; // Two dim assign

int d[]=a[0][0]; // One dim assign

Ex 4

int a[][][][]=new int[2][2][2][2] ;

int b[][]=a[0][0]; // Two dim assign

int c[][][]=a[0]; // Three dim assign

int d[][][][]=a;// Four dim assign