没有区别。看看 Java语言规范，第3.10.2节

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

DecimalFloatingPointLiteral：

1. 数位。数位 _opt ExponentPart _opt FloatTypeSuffix _opt


2. 。数字ExponentPart _opt FloatTypeSuffix _opt


3. 数字ExponentPart FloatTypeSuffix _opt


4. Digits ExponentPart _opt FloatTypeSuffix

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

...

FloatTypeSuffix：

f F d D

都是一个 DecimalFloatingPointLiteral ，第一个类型1，第二个类型4

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