浮点字面值中“0”作为前缀的含义是什么？

Question

Using "0" (zero) as a prefix in an integer literal changes its base to octal. This is why

System.out.println(010);

will print 8 . But using "F" as a suffix

System.out.println(010F);

will make it float losing octal base (going back to decimal) and will print 10.0 .

Is there any difference between 010F and 10F ? Has the "0" prefix any kind of meaning when working with floats?

Answer 1

From the Java Language Specification, on Floating Point literals

FloatingPointLiteral:

• DecimalFloatingPointLiteral
• HexadecimalFloatingPointLiteral

DecimalFloatingPointLiteral:

• Digits . [Digits] [ExponentPart] [FloatTypeSuffix]
• . Digits [ExponentPart] [FloatTypeSuffix]
• Digits ExponentPart [FloatTypeSuffix]
• Digits [ExponentPart] FloatTypeSuffix

where Digits

Digits:

• Digit
• Digit [DigitsAndUnderscores] Digit

Digit:

• 0
• NonZeroDigit

DigitsAndUnderscores:

• DigitOrUnderscore {DigitOrUnderscore}

DigitOrUnderscore:

• Digit
• _

Underscores:

• _ {_}

You can have any number of leading 0 for floating point literals.

I cannot find anything in the JLS that explains why this is allowed, but I can imagine it simplifies parsing.

Answer 2

Octal notation is only used for integers, not for floating point numbers. This is not specific to Java. So the extra 0 has no effect (other than being confusing for the human reader).

Answer 3

Only Integer Literals can be represented in Octal form(Base-8) in Java.

jls-3.10.1 : Integer Literals

Floating point numbers can be represented either in Decimal (or) Hexadecimal form only.

jls-3.10.2 : Floating Literals