Java: Why can't I declare integer types using scientific notation?

Question

I can easily read 2e15 as "two quadrillion" at a glance, but for 2000000000000000 I have to count the zeroes, which takes longer and can lead to errors.

Why can't I declare an int or long using a literal such as 2e9 or 1.3e6? I understand that a negative power of 10, such as 2e-3, or a power of 10 that is less than the number of decimal places, such as 1.0003e3, would produce a floating point number, but why doesn't Java allow such declarations, and simply truncate the floating-point part and issue a mild warning in cases where the resulting value is non-integral?

Is there a technical reason why this is a bad idea, or is this all about type-safety? Wouldn't it be trivial for the compiler to simply parse a statement like

long x = 2e12 as long x = 2000000000000 //OK for long

and int y = 2.1234e3 as int y = 2123.4 //warning: loss of precision

Answer 1

It's because when you use the scientific notation you create a floating point number (a double in your example). And you can't assign a floating point to an integer (that would be a narrowing primitive conversion, which is not a valid assignment conversion).

So this would not work either for example:

int y = 2d; //can't convert double to int

You have a few options:

• explicitly cast the floating point to an integer: int y = (int) 2e6;
• with Java 7+ use a thousand separator: int y = 2_000_000;

Answer 2

Because it's a shortcoming of Java.

(Specifically, there is clearly a set of literals represented by scientific notation that are exactly represented by ints and longs, and it is reasonable to desire a way to express those literals as ints and longs. But, in Java there isn't a way to do that because all scientific notation literals are necessarily floats because of Java's language definition.)

Answer 3

You are asking about the rules on writing a integer literals. See this reference: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html The capability to use scientific notation as an integer literal might make things easier indeed but has not been implemented. I do not see any technical reason that would prevent such a feature from being implemented.