posted 11 years ago
42L is boxed to a Long, but in the comparison it is autounboxed.
Originally posted by Justyna Wozniak:
Hello,
this question is based on K&B, page 302, Q3.
Why does the following piece of code compile:
?
Does x get unboxed to a long and then converted to a float?
Or is x.floatValue() called?
Thanks,
Justyna W.
42L is boxed to a Long, but in the comparison it is autounboxed.
Keith Lynn
Ranch Hand
Posts: 2410
posted 11 years ago
Yes, it is converted back to a long, and then the normal rules of binary promotion will promote it to a float since the other operand is a float.
For reference, section 5.6.2 of the Java Language Specification defines binary numeric promotion.
5.6.2 Binary Numeric Promotion
When an operator applies binary numeric promotion to a pair of operands, each of which must denote a value that is convertible to a numeric type, the following rules apply, in order, using widening conversion (�5.1.2) to convert operands as necessary:
* If any of the operands is of a reference type, unboxing conversion (�5.1.8) is performed. Then:
* If either operand is of type double, the other is converted to double.
* Otherwise, if either operand is of type float, the other is converted to float.
* Otherwise, if either operand is of type long, the other is converted to long.
* Otherwise, both operands are converted to type int.
After the type conversion, if any, value set conversion (�5.1.13) is applied to each operand.
Binary numeric promotion is performed on the operands of certain operators:
* The multiplicative operators *, / and % (�15.17)
* The addition and subtraction operators for numeric types + and  (�15.18.2)
* The numerical comparison operators <, <=, >, and >= (�15.20.1)
* The numerical equality operators == and != (�15.21.1)
* The integer bitwise operators &, ^, and  (�15.22.1)
* In certain cases, the conditional operator ? : (�15.25)
For reference, section 5.6.2 of the Java Language Specification defines binary numeric promotion.
5.6.2 Binary Numeric Promotion
When an operator applies binary numeric promotion to a pair of operands, each of which must denote a value that is convertible to a numeric type, the following rules apply, in order, using widening conversion (�5.1.2) to convert operands as necessary:
* If any of the operands is of a reference type, unboxing conversion (�5.1.8) is performed. Then:
* If either operand is of type double, the other is converted to double.
* Otherwise, if either operand is of type float, the other is converted to float.
* Otherwise, if either operand is of type long, the other is converted to long.
* Otherwise, both operands are converted to type int.
After the type conversion, if any, value set conversion (�5.1.13) is applied to each operand.
Binary numeric promotion is performed on the operands of certain operators:
* The multiplicative operators *, / and % (�15.17)
* The addition and subtraction operators for numeric types + and  (�15.18.2)
* The numerical comparison operators <, <=, >, and >= (�15.20.1)
* The numerical equality operators == and != (�15.21.1)
* The integer bitwise operators &, ^, and  (�15.22.1)
* In certain cases, the conditional operator ? : (�15.25)
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