从Java语言规范，在浮点文字

FloatingPointLiteral：

• DecimalFloatingPointLiteral


• 
  
  
  
  
  
  
  
  
  
  
  $
• 数字。 [Digits] [ExponentPart] [FloatTypeSuffix]


• 。 Digits [ExponentPart] [FloatTypeSuffix]


• 数字ExponentPart [FloatTypeSuffix]


• 数字[ExponentPart] FloatTypeSuffix
  

>

其中数字

位数：

• 数字


• 数字 [DigitsAndUnderscores] Digit

DigitAndUnderscores：

• DigitOrUnderscore {DigitOrUnderscore}

DigitOrUnderscore：

• 数字
  
• _



下划线： / ul>

对于浮点文字，您可以有任意数量的前导 0 。

我无法在JLS中找到任何解释为何允许这样做的内容，但是我可以想象它简化了解析。

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?

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.