Arrays java

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                       Arrays

==================================

 

1. Introduction:

            indexed collection of homogenous data.

 

          Advantage:

                 we can represent the huge number of values / data using a single variable.

 

      Disadvantage:

                 Arrays are fixed in size.

                      ==> once array size fixed we can't increase or decrease the size of an array.

                      ==> if we are using arrays concept in advance we need  know the size of an array. (this may not be possible always).

 

2. Array Declaration:

      1D Array:

            int[] x; -----> Recommended to use

 

           int x[];

 

           int []x;

       ==> At the time of array declartion we can't specify the size of an array.

 

       int[6] x; --->  X--- Compile time error 😥😥😥

 

       int[] x; 👌👌👌

 

 

       2D array Declartion:

 

       int[][] x;

 

       int [][]x;

 

       int x[][];

       

       int[] []x;

 

       int[] x[];

 

       int []x[];

 

 

which of the following ara valid?

 

int[] a[],b;  ====> a = 2, b = 1

 

int[] a[],b[]; ====> a = 2, b = 2;

 

int[] []a,b; ====> a = 2, b = 2;

 

int[] []a,b[]; ====> a = 2, b = 3; 👌👌👌

 

int[] []a,[]b; ====>  Compile time error - 😥😥😥

 

 

3D array declaration:

 

     int[][][] a;

 

 

array creation:

      --> in java every array is an object.

 

      using new operator.

 

      ex:

            int[] name = new int[6];

 

 

loopholes:

 

1) at the time of array creation only we need to specify the size. otherwise we will get compile time error.

 

      int[] name = new int[6];  👌👌👌👌👌

 

      int[] name = new int[]; ==> CE 😥😥😥

 

 

2)    int[] name = new int[0]; 👌👌👌👌👌

 

3)          int[] name = new int[-6]; ==> Run time Error --> negative array size exception 😥😥😥

 

4) To specify the array size allowed data types are byte, short, int, char.

 ===> if trying to specify the any other types then we will get compile time error.

 

 int[] name = new int[10];

 

 5) the maximum allowed array size in java 2147483647. this is the maximum int value.

 

 int[] name = new int[2147483647]; 👌👌👌👌👌

 

 int[] name = new int[2147483648]; 😥😥😥 --> compile time error int value is too large

 

 

4. Array Intilization:

 

 int[] name = new int[10]; ---> intilized with default values.

 

  int[][] name = new int[2][3];

 

 

  int[][] name = new int[2][];

 

  System.out.println(name);

 

  System.out.println(name[0]);----> null

 

  System.out.println(name[0][0]); ==> 😥😥😥 Run time error --> null point exception

 

  intilization:

 

  int[] a = new int[6];

 

  a[0]= 10;

  a[1]= 20;

  a[2]= 30;

  a[3]= 40;

  a[4]= 50;

  a[5]= 60;

 

  a[6]= 10; ==> RE: index out of bond exception 😥😥😥

 

  a[-5]= 100; ==> RE: 😥😥😥

 

  a[2.8] = 15; ==> CE: found: Double, required: int 😥😥😥

 

====================================================================

                 Array declartion creation and intilization in a

                                             single line

=====================================================================

 

1D array:

 

declartion: int[] a;

 

creation: a = new int[3];

 

installzation:

 

  a[0]= 10;

  a[1]= 20;

  a[2]= 30;

  --------------------

  single line

  -----------------

 

  int[] a = {10,20,30};

 

 

 

 ---------------------------

 2D array

 ---------------------------

 

 int[][] a = {{10,20},{1,2,3}};

 

 ------------------

 3D array

 -------------

 

 

 

int[][][] a = {{{10,20},{1,2,3}},{{10,20},{1,2,3}},{{10,20},{1,2,3}}}

 

 

Annonymous array:

 

main purpose only one time use

 

creation:

new int[] {10,20,30};

 

new int[3] {10,20,30}; 😥😥😥 ==> CE

 

 

int[] x = new int[] {10,20,30}; ----> it is not annonymous any more.

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