1D and 2D arrays in java

1D arrays in java

1. Syntax to declare an integer array in java
   int []a;  or int a[];   or int[] a;
2. Allocating memory to store 3 integers (instantiation)
   a=new int[3];
   you can declare and instantiate in same line by writing int a[]=new int[3];
3.  Initialization or giving values
   a[0]=2;
   a[1]=12;
   a[2]=5;
   (or) take array values from user
   for(int i=0; i< a.length;i++)
               a[i]=sc.nextInt();
   here sc is an object of Scanner class
4. you can declare, instantiate and initialize in same line as int a[]={1,2,3,4};
5. Displaying all elements of array using for each loop
   for(int ele: a)
           System.out.println(ele);
   
6.  Displaying elements using for loop
   for(int i=0; i< a.length;i++)
               System.out.println(a[i]);
   here length is a property of arrays that will return the size of array
7. Linear Search function in java that returns index if search element found otherwise returns -1
   public static int linearSearch(int a[],int key)
   {
          for(int i=0;i<a.length;i++)
          {
                    if(a[i] == key)
                           return i;
           }
           return -1;
   }

2D arrays in java

Declaration:

int[][] a;  or int[][] a;   or int [][]a;

Instantiation:

a = new int[3][3];

We can do declaration and instantiation in same line by writing int a[][] = new int[3][3];

Initialization and giving values

for(int i=0;i<a.length;i++)
{

           for(int j=0;j<a[i].length;j++)

                     a[i][j]=sc.nextInt();

}

here  a.length will give number of rows and a[i].length gives number of columns in each row.

and sc is object of Scanner class

Initialization, instantiation and initialization in single line

int a[][]={{1,2,3},{4,5,6},{7,8,9}};