Java Arrays

Arrays are used to put similar types of multiple variables.
Arrays can hold similar types of objects or primitive types.
Array variables are always considered as object in java.

Declaration of Array

int[]  a;
int   a[];
Object[ ]  obj;
Object  obj[];
// square bracket or after the variable both are recommended.
//2 -d array
int [][] a2;
int a2 [][];
Object[ ][]  obj;
Object  obj[][] ;

Instantiating or Constructing an Array

Declaration of an array does not mean a heap space is allocated for that array.Heap space is allocated when an array is instantiated or created.
 During the construction of an Array object  we need to mention the size of that object.

a = new int[6];
obj = new Object[10];
// 2-d array
 a2 = new int[4][5];
 a3 = new int[4][]; 
 obj2 = new Object[3][4]; 

 

Initializing an Array

We  have already declared and initialized an Array now we need to learn how to put values on the initialized array.

a[0] = 10;
a[1] = 20;
a[2] = 30;
a[3] = 40;
a[4] = 60;
a[5] = 70;

obj[0] = new Object();
obj[1] = new Object();

2 D Array

a2[0] = new int[3];
a2[1] = new int[4];
a2[2] = new int[5];
a2[3] = new int[6];

a2[0][1] = 10;
a2[1][3] = 20;
a2[2][1] = 30;
a2[2][4] = 50;
a2[3][4] = 40;