CHAPTER 15: Expressions

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15.13 Postfix Expressions

Postfix expressions include uses of the postfix ++ and -- operators. Also, as discussed in S15.7, names are not considered to be primary expressions, but are handled separately in the grammar to avoid certain ambiguities. They become interchangeable only here, at the level of precedence of postfix expressions.

PostfixExpression:

	Primary

	ExpressionName

	PostIncrementExpression

	PostDecrementExpression

15.13.1 Names

A name occurring in an expression may be, syntactically, an ExpressionName (S6.5). The meaning of such an ExpressionName depends on its form:

• If it is a simple name, that is, just an Identifier, then there are two cases:
  • If the Identifier occurs within the scope of a parameter or local variable named by that same Identifier, then the type of the ExpressionName is the declared type of the parameter or local variable; moreover, the value of the ExpressionName is a variable, namely, the parameter or local variable itself.
  • Otherwise, the ExpressionName is treated exactly as if it had been the field access expression (S15.10):

  this. Identifier containing the keyword this (S15.7.2).

• Otherwise, if it is a qualified name of the form PackageName . Identifier, then a compile-time error occurs.
• Otherwise, if it is a qualified name of the form TypeName . Identifier, then it is refers to a static field of the class or interface named by the TypeName. A compile-time error occurs if TypeName does not name a class or interface. A compile-time error occurs if the class or interface named by TypeName does not contain an accessible static field named by the Identifier. The type of the ExpressionName is the declared type of the static field. The value of the ExpressionName is a variable, namely, the static field itself.
• Otherwise, it is a qualified name of the form Ename . Identifier, where Ename is itself an ExpressionName, and the ExpressionName is treated exactly as if it had been the field access expression (S15.10): ( Ename). Identifier

containing a parenthesized expression (S15.7.3).

15.13.2 Postfix Increment Operator ++

PostIncrementExpression:

	PostfixExpression ++

A postfix expression followed by a ++ operator is a postfix increment expression. The result of the postfix expression must be a variable of a numeric type, or a compile-time error occurs. The type of the postfix increment expression is the type of the variable. The result of the postfix increment expression is not a variable, but a value.

At run time, if evaluation of the operand expression completes abruptly, then the postfix increment expression completes abruptly for the same reason and no incrementation occurs. Otherwise, the value 1 is added to the value of the variable and the sum is stored back into the variable. Before the addition, binary numeric promotion (S5.6.2) is performed on the value 1 and the value of the variable. If necessary, the sum is narrowed by a narrowing primitive conversion (S5.1.3) to the type of the variable before it is stored. The value of the postfix increment expression is the value of the variable before the new value is stored.

A variable that is declared final cannot be incremented, because when an access of 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.

15.13.3 Postfix Decrement Operator --

PostDecrementExpression:

	PostfixExpression --

A postfix expression followed by a -- operator is a postfix decrement expression. The result of the postfix expression must be a variable of 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 occurs. 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 (S5.6.2) is performed on the value 1 and the value of the variable. If necessary, the difference is narrowed by a narrowing primitive conversion (S5.1.3) 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.

A variable that is declared final cannot be decremented, because when an access of 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.