Expressions - The Java Language Specification - page 499

Note that the binary numeric promotion mentioned above may include unboxing con-
version (§ 5.1.8 ) and value set conversion (§ 5.1.13 ) . If necessary, value set conversion
is applied to the sum prior to its being stored in the variable.
A variable that is declared final cannot be incremented because when an access of such a
final variable is used as an expression, the result is a value, not a variable. Thus, it cannot
be used as the operand of a postfix increment operator.
15.14.3. Postfix Decrement Operator --
A postfix expression followed by a -- operator is a postfix decrement expression.
PostDecrementExpression:
PostfixExpression --
The result of the postfix expression must be a variable of a type that is convertible (§ 5.1.8 )
to a numeric type, or a compile-time error occurs.
The type of the postfix decrement expression is the type of the variable. The result of the
postfix decrement expression is not a variable, but a value.
At run time, if evaluation of the operand expression completes abruptly, then the postfix
decrement expression completes abruptly for the same reason and no decrementation oc-
curs. Otherwise, the value 1 is subtracted from the value of the variable and the difference
is stored back into the variable. Before the subtraction, binary numeric promotion (§ 5.6.2 )
is performed on the value 1 and the value of the variable. If necessary, the difference is nar-
rowed by a narrowing primitive conversion (§ 5.1.3 ) and/or subjected to boxing conversion
(§ 5.1.7 ) to the type of the variable before it is stored. The value of the postfix decrement
expression is the value of the variable before the new value is stored.
Note that the binary numeric promotion mentioned above may include unboxing con-
version (§ 5.1.8 ) and value set conversion (§ 5.1.13 ) . If necessary, value set conversion
is applied to the difference prior to its being stored in the variable.
A variable that is declared final cannot be decremented because when an access of such a
final variable is used as an expression, the result is a value, not a variable. Thus, it cannot
be used as the operand of a postfix decrement operator.
15.15. Unary Operators
The operators + , - , ++ , -- , ~ , ! , and the cast operator (§ 15.16 ) are called the unary operators .
UnaryExpression: