Java Widening and narrowing conversions

When one type of variable (source) is assigned to another type of variable (destination), an automatic type conversion will occur if the type of the destination variable wide is enough and able to hold the entire range of the source variable. Automatic type conversion is also called as widening conversion.

Following table shows the width and ranges of primitive data types.

Type	Width in bits	How range is derived	Range
Char	16	2^16	0 to 65,536
Integer data types
Byte	8	(-2^7) to (2^7-1)	-128 to +127
Short	16	(-2^15) to (2^15-1)	-32,768 to +32,767
Int	32	(-2^31) to (2^31-1)	-2,147,483,648 to +2,147,483,647
Long	64	(-2^63) to (2^63-1)	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
Floating-point data types
Float	32	IEEE-754 standard	1.4e-045 to 3.4e+038
Double	64	IEEE-754 standard	4.9e-324 to 1.8e+308

In the below table, cells highlighted in Green results in the widening conversion and the cells highlighted in blue results in the “narrowing conversion”.

The cells highlighted in blue will result in compilation error unless we explicitly cast the source variable type to the destination variable type.

char = char	byte = byte	short = byte	int = char	long = char	float = char	double = char
char = byte	byte = char	short = short	int = byte	long = byte	float = byte	double = byte
char = short	byte  = short	short = char	int = short	long = short	float = short	double = short
char = int	byte  = int	short  = int	int = int	long = int	float = int	double = int
char = long	byte  = long	short  = long	int = long	long = long	float = long	double = long
char = float	byte  = float	short  = float	int = float	long = float	float = float	double = float
char = double	byte  = double	short  = double	int = double	long = double	float = double	double = double

Example for widening conversion

In the below example, char variable ‘charVar’ is assigned to an integer variable ‘intVar’. Since integer can hold entire range of char values, this assignment is allowed. Java internally converts the Unicode value of the ‘charVar’ to 32 bit integer value and assigns it to ‘intVar’.

class MyClass {

       public static void main(String arg[]) {

              int intVar;

              char charVar = 'x';

              intVar = charVar;

       }

}

Example for narrowing conversion

A ‘char’ variable cannot be assigned integer, floating-point variables because it won’t be able to hold entire range of those data types. So, to make the assignment to work, we need to explicitly cast the source variable type to char.

In the below example, integer variable ‘intVar’ is cast to ‘char’ to avoid the compilation error.

class MyClass {

       public static void main(String arg[]) {

              int intVar = 100;

              char charVar;

              charVar = (char)intVar;

       }

}

Note that narrowing conversion may result in the loss of precision.