double field type declaration as zero

问题

What is significant difference between following zero double variable declaration: 0.0 VS 0d

double d1 = 0.0;
double d2 = 0d;

I understand that both these are better than just 0,because are more obvious for code reader.

However 0.0 VS 0d difference is not clear for me.

回答1:

There is no difference. Have a look at the Java Language Specification, section 3.10.2

DecimalFloatingPointLiteral:

1. Digits . Digits_optExponentPart_optFloatTypeSuffix_opt
2. . Digits ExponentPart_optFloatTypeSuffix_opt
3. Digits ExponentPart FloatTypeSuffix_opt
4. Digits ExponentPart_optFloatTypeSuffix

...

FloatTypeSuffix: one of

f F d D

Both are a DecimalFloatingPointLiteral, the first one type 1, the second one type 4

回答2:

Go check out the JLS section on floating point literals:

A floating-point literal is of type float if it is suffixed with an ASCII letter F or f; otherwise its type is double and it can optionally be suffixed with an ASCII letter D or d.

So it's a double if it's not suffixed

来源：https://stackoverflow.com/questions/16543025/double-field-type-declaration-as-zero