Data Types_premitive

Java Data Types  Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory Based on the data type of a variable, the operating system allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals, or characters in these variables

There are two data types available in Java:

• Primitive Data Types
• Reference/Object Data Types 

Primitive Data Types:  There are eight primitive data types supported by Java. Primitive data types are predefined by the language and named by a keyword.

Sample Program :

public class DataTypesde

{

          public static void main(String[] args)

          {

// int

                   int i=10;

                   System.out.println(i);     //10

                   System.out.println(Integer.MAX_VALUE);         //2147483647

                   System.out.println(Integer.MIN_VALUE);                    //-2147483648

                   System.out.println(Integer.SIZE);                             //32

// double

                   double d=20.9;

                   double d1=20;

          System.out.println(d);                                                      //20.9

          System.out.println(d1);                                                    //20.0

          System.out.println(Double.MAX_VALUE);                //1.7976931348623157E308

          System.out.println(Double.MIN_VALUE);                 //4.9E-324

          System.out.println(Double.SIZE);                            //64

//char

          char c='a';

          char c2='d';

          System.out.println(c);                                                      //a

          System.out.println(c2);                                                    //b

          System.out.println(Character.MAX_CODE_POINT);   //1114111

          System.out.println(Character.MAX_VALUE);           //

          System.out.println(Character.MAX_VALUE);

    System.out.println(Character.SIZE);                              //16

          // string

          String s1="anji";                                                              //anji

          System.out.println(s1);

// float

          float f=10;

          float f2=10;

          System.out.println(Float.MAX_VALUE);                   //3.4028235E38

          System.out.println(Float.MIN_VALUE);           //1.4E-45

          System.out.println(Float.SIZE);                               //32

          System.out.println(f);                                                       //10.0

// byte

          byte b1=10;

          System.out.println(b1);                                           //10

          System.out.println(Byte.SIZE);                      //8

          System.out.println(Byte.MAX_VALUE);          //127

          System.out.println(Byte.MIN_VALUE);            //-128

//short

      short sh=25;

       System.out.println(sh);                                    //25

       System.out.println(Short.MAX_VALUE);  //32767

       System.out.println(Short.MIN_VALUE);   //-32768

       System.out.println(Short.SIZE);              //16

// long

    long t=123;

    System.out.println(t);                               //123

    System.out.println(Long.MAX_VALUE);      //9223372036854775807

    System.out.println(Long.MIN_VALUE);       //-9223372036854775808

    System.out.println(Long.SIZE);                  //64

          }

}

Data types and default size:

Data Type	Default Value	Default size
boolean	false	1 bit
char	'\u0000'	2 byte
byte	0	1 byte
short	0	2 byte
int	0	4 byte
long	0L	8 byte
float	0.0f	4 byte
double	0.0d	8 byte

Java Varibles

We would see following type of variables in Java:

• Local Variables
• Global variables

Local Variables : - A variable that is declared inside the method or block  is called local variable. Local variables within the method or block others methods or block can’t be used .There is no default values

public class localVariables

{

//local variables can be declared within the block

          static

          {

          float f;

System.out.println(f);                                             //CTE

                   f=10;

          System.out.println(f);

          }

// iib block

          {

                   double d;

                   System.out.println(d);                           //CTE

 //local variables can be declared within the method and should be instilized

                   d=10.5;

                   System.out.println(d);

          }

//local variables can be declared within the method

          void method1()

          {

                   int u;

                   System.out.println(u);

//local variables can be declared within the method and should be instilized

                   u=20;

                   System.out.println(u);

//local variables can't be out side

                   System.out.println(i);                 //CTE

                  

          }

// CONSTRUCTOR

          LocalVariables()

          {

                   int t;

                   System.out.println(t);                          //cte

                   t=56;

                   System.out.println(t);

          }

     public static void main(String[] args)

       {

           //object creation

           localVariables v1=new localVariables();

                     int i=10;

           System.out.println(i);                           //10

//local varibles should be instlized

           int j;

           System.out.println(j);                                   //CTE

 //local varibles should be used after the instilization only

           int k;

           int y=k;

           System.out.println(y);               // IILEGAL FORWARD REF

//local varibles any times of reinstilized

           i=20;

           System.out.println(i);

           i=50;

           System.out.println(i);

 //local variables can't be out side

                   system.out.println(u);                         // CTE

      

       }

}

Global variables :

Global variables contains default values its is based on the relevant data types

We can use any where in the class it’s based on type of global variables.

Class Variables :-

• Class variables are variables declared with in a class, outside any method, with the static keyword.
• Whenever the class loaded into the memory automatically loaded into static variables before main method

A class can have any number of methods to access the value of various kinds of methods

Default values for static variables  :

public class Defultvalues

{

          int i;

          String s1;

          double d;

          long l;

          float f;

          char c;

          boolean b;

          byte y;

          public static void main(String[] args)

          {

defultvalues v1=new defultvalues();

System.out.println(v1.i);            //0

System.out.println(v1.s1);          //null

System.out.println(v1.d);           //0.0

System.out.println(v1.l);            //0

System.out.println(v1.f);            //0.0

System.out.println(v1.c);           //single space

System.out.println(v1.b);  //false

System.out.println(v1.y);           //0

          }

}

Simple Program :

public class Staticv

{

// static varibles declaration

          static int i;

static

{

          static int h=50;                                             //cte

          System.out.println(i);                                    // cts

}        

          public static void main(String[] args)

          {

          // static varibles can't be used in side main method

          static double d=10;                                        //cte

          System.out.println(i);                                    // 0  

          }

}

Instance Variables (Non-static variables) : A variable that is declared inside the class but outside the method is called instance variable . It is not declared as static. public class Instancevariables { // non static varibles             int i=10;             double d=10;             int test1(int i)             {                      System.out.println(i);                                         return i;             }                       public static void main(String[] args)           {                    int j=10;                    Instancevariables ref=new Instancevariables();       // non static varbiles can be used when ever craeating object                    System.out.println(i);       // cte if cts i declared as static                    System.out.println(ref.i);                    System.out.println(ref.j);  //cte                    ref.i=20;                    //test1(ref.j); //non static members can be calling with ref of object                    ref.test1(10);                              } } Default values: In java default some value will be assigned  in the variables based on data type public class Defultvalues {           int i;           String s1;           double d;           long l;           float f;           char c;           boolean b;           byte y;           public static void main(String[] args)           { defultvalues v1=new defultvalues(); System.out.println(v1.i);            //0 System.out.println(v1.s1);          //null System.out.println(v1.d);           //0.0 System.out.println(v1.l);            //0 System.out.println(v1.f);            //0.0 System.out.println(v1.c);           //single space System.out.println(v1.b);  //false System.out.println(v1.y);           //0           } }

Default values

public class Defultvalues

{

          int i;

          String s1;

          double d;

          long l;

          float f;

          char c;

          boolean b;

          byte y;

          public static void main(String[] args)

          {

defultvalues v1=new defultvalues();

System.out.println(v1.i);            //0

System.out.println(v1.s1);          //null

System.out.println(v1.d);           //0.0

System.out.println(v1.l);            //0

System.out.println(v1.f);            //0.0

System.out.println(v1.c);           //single space

System.out.println(v1.b);  //false

System.out.println(v1.y);           //0

          }

}