Type conversion

Type Casting  refers to changing an entity of one datatype into another. This is important for the type conversion in developing any application. If you will store a int value into a byte variable directly, this will be illegal operation. For storing your calculated int value in a byte variable you will have to change the type of resultant data which has to be stored.

Automatic Conversion

In Java type conversions are performed automatically when the type of the expression on the right hand side of an assignment operation can be safely promoted to the type of the variable on the left hand side of the assignment. Thus we can safely assign:

byte -> short -> int -> long -> float -> double

lets take an example,

// 64 bit long integer

long myLongValue;

// 32 bit standard integer 

int myIntValue;

myLongValue = myIntValue;

Java follows two types of casting

• Upcasting
•  Downcasting

Upcasting

Casting a reference with the class hierarchy in a direction from the sub classes towards the root then this type of casting is termed as upcasting. Upcasting does not require a cast operator.

DownCasting

On the other hand, casting a reference with hierarchal class order in a direction from the root class towards the children or subclasses, then it is known as downcasting.

Here we discussing one example,where we converting int value to byte.

int x=10;

byte b =(byte) x;

here first we assign the int x to 10;Then we try to convert int x to byte and try to store in the variable byte b.for that we using byte b =(byte) x;

Explicit Conversion (Casting)

Automatic type casting does work in case of narrowing i.e. when a data type requiring more storage is converted into a data type that requires less storage. E.g. conversion of a long to an int does not perform because the first requires more storage than the second and consequently information may be lost. In such situations an explicit conversion is required. 

Variable declaration

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.

In java programing language all variables must first be declared before they can be used.This structure involves starting the variable’s type and name.

int nm=1;

Doing so tells your program that a field named “nm” using to hold numerical data .Where “int” is the variable data type and “nm” is the variable name.where we initializing the integer nm value as 1.

byte:

• Byte data type is a 8-bit signed two's complement integer.
• Minimum value is -128 (-2^7)
• Maximum value is 127 (inclusive)(2^7 -1)
• Default value is 0
• Byte data type is used to save space in large arrays, mainly in place of integers, since a byte is four times smaller than an int.
• Example : byte a = 100 , byte b = -50

short:

• Short data type is a 16-bit signed two's complement integer.
• Minimum value is -32,768 (-2^15)
• Maximum value is 32,767(inclusive) (2^15 -1)
• Short data type can also be used to save memory as byte data type. A short is 2 times smaller than an int
• Default value is 0.
• Example : short s= 10000 , short r = -20000

int:

• Int data type is a 32-bit signed two's complement integer.
• Minimum value is - 2,147,483,648.(-2^31)
• Maximum value is 2,147,483,647(inclusive).(2^31 -1)
• Int is generally used as the default data type for integral values unless there is a concern about memory.
• The default value is 0.
• Example : int a = 100000, int b = -200000

long:

• Long data type is a 64-bit signed two's complement integer.
• Minimum value is -9,223,372,036,854,775,808.(-2^63)
• Maximum value is 9,223,372,036,854,775,807 (inclusive). (2^63 -1)
• This type is used when a wider range than int is needed.
• Default value is 0L.
• Example : int a = 100000L, int b = -200000L

float:

• Float data type is a single-precision 32-bit IEEE 754 floating point.
• Float is mainly used to save memory in large arrays of floating point numbers.
• Default value is 0.0f.
• Float data type is never used for precise values such as currency.
• Example : float f1 = 234.5f

double:

• double data type is a double-precision 64-bit IEEE 754 floating point.
• This data type is generally used as the default data type for decimal values. generally the default choice.
• Double data type should never be used for precise values such as currency.
• Default value is 0.0d.
• Example : double d1 = 123.4

boolean:

• boolean data type represents one bit of information.
• There are only two possible values : true and false.
• This data type is used for simple flags that track true/false conditions.
• Default value is false.
• Example : boolean one = true

char:

• char data type is a single 16-bit Unicode character.
• Minimum value is '\u0000' (or 0).
• Maximum value is '\uffff' (or 65,535 inclusive).
• Char data type is used to store any character.
• Example . char letterA ='A'