Java primitives conversion & operations

First, booleans

Booleans cannot be assigned to any other types, and you can't do any arithmetic on them. So true doesn't count as 1, nor does 1 count as true. No truthy and falsy in Java.

Converting: `a = b`

Some types can only be converted if you cast explicitly. These are usually the cases where a type with a wider or different range is converted to one with a narrower range. If you use explicit casting, you might be changing to a nonsense value if it's outside the range of the target.

from / into	byte	short	char	int	long	float	double
byte		implicit	explicit	implicit	implicit	implicit	implicit
short	explicit		explicit	implicit	implicit	implicit	implicit
char	explicit	explicit		implicit	implicit	implicit	implicit
int	explicit	explicit	explicit		implicit	implicit	implicit
long	explicit	explicit	explicit	explicit		implicit	implicit
float	explicit	explicit	explicit	explicit	explicit		implicit
double	explicit	explicit	explicit	explicit	explicit	explicit

Arithmetic: `a + b`

This table shows the output for arithmetic operations between two variables. For example, long * float becomes a float.

	byte	short	char	int	long	float	double
byte	integer	integer	integer	integer	long	float	double
short	integer	integer	integer	integer	long	float	double
char	integer	integer	integer	integer	long	float	double
int	integer	integer	integer	integer	long	float	double
long	long	long	long	long	long	float	double
float	float	float	float	float	float	float	double
double	double	double	double	double	double	double	double

Integers versus decimals

Note that this does not mean that information cannot be lost! For example, Long.MAX_VALUE = 9223372036854775807, but when stored as a float it is approximated as 9223372036854776000 in a float: a big difference.

float and double don't have uniform spacings between adjacent representable values. Low values are much closer together than high values. The spacing between two values that can be represented exactly is much greater than 1 for high values (so a + 1.0 might be a if it is a float or double). You might have expected this, since a int has 4 bytes with range from -2^31 to +2^31-1 possible values, where float also has 4 bytes but has a much bigger range (2^(2^7) = 3.4e38). Obviously it cannot store all the numbers that integer can, there aren't enough bytes (and that ignores non-integer numbers).

So what this means, is that although you can store integers are decimals without explicit casting, you might still lose precision for higher integers.

First, booleans

Converting: a = b

Arithmetic: a + b

Integers versus decimals

Converting: `a = b`

Arithmetic: `a + b`