java - why explicit type casting required from double to float but not from int to byte?

Question

Consider following statement:

byte by = 5; //works fine

literal '5' is of type int and small enough to fit into a variable of type byte. Compiler does the implicit type casting here (from int to byte).

Now consider following scenario:

float fl = 5.5;    //compilation error

literal '5.5' is of type double, also small enough to fit into a variable of type float. Why do we need to explicitly type cast like this:

float fl = (float) 5.5;   //works fine

Why compiler is not doing the casting for us in case of floating points?

Answer 1

In the integer version, the compiler knows that all the data in the number 5 can be stored in a byte. No information is lost. That's not always true for floating point values. For example, 0.1f isn't equal to 0.1d.

Now for the example, you've given, the decimal value 5.5 is exactly represented in both float and double, so you could argue that in that case, no information is lost - but it would be pretty odd for the language specification to have to make this valid:

float f = 5.5;

but this invalid:

float f = 5.6;

The language specification is happy to talk about whether a number fits within the range of float/double (although even that isn't as simple as you might expect) but when it comes to whether a literal can be exactly represented, I don't think it ever goes into detail.