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.A cast operator has no effect on the choice of value set for a value of type float or type double.Consequently, a cast to type float within an expression that is not FP-strict does not necessarily cause its value to be converted to an element of the float value set, and a cast to type double within an expression that is not FP-strict does not necessarily cause its value to be converted to an element of the double value set.At run time, the operand value is converted by casting conversion to the type specified by the cast operator.Not all casts are permitted by the language.Some casts result in an error at compile time.For example, a primitive value may not be cast to a reference type.Some casts can be proven, at compile time, always to be correct at run time.For example, it is always correct to convert a value of a class type to the type of its superclass; such a cast should require no special action at run time.Finally, some casts cannot be proven to be either always correct or always incorrect at compile time.Such casts require a test at run time.A ClassCastException is thrown if a cast is found at run time to be impermissible.15.17 Multiplicative OperatorsThe operators *, /, and % are called the multiplicative operators.They have the same precedence and are syntactically left-associative (they group left-to-right).MultiplicativeExpression:UnaryExpressionMultiplicativeExpression * UnaryExpressionMultiplicativeExpression / UnaryExpressionMultiplicativeExpression % UnaryExpressionThe type of each of the operands of a multiplicative operator must be a primitive numeric type, or a compile-time error occurs.Binary numeric promotion is performed on the operands.The type of a multiplicative expression is the promoted type of its operands.If this promoted type is int or long, then integer arithmetic is performed; if this promoted type is float or double, then floating-point arithmetic is performed.Note that binary numeric promotion performs value set conversion.15.17.1 Multiplication Operator *The binary * operator performs multiplication, producing the product of its operands.Multiplication is a commutative operation if the operand expressions have no side effects.While integer multiplication is associative when the operands are all of the same type, floating-point multiplication is not associative.If an integer multiplication overflows, then the result is the low-order bits of the mathematical product as represented in some sufficiently large two's-complement format.As a result, if overflow occurs, then the sign of the result may not be the same as the sign of the mathematical product of the two operand values.The result of a floating-point multiplication is governed by the rules of IEEE 754 arithmetic:lIf either operand is NaN, the result is NaN.lIf the result is not NaN, the sign of the result is positive if both operands have the same sign, and negative if the operands have different signs.lMultiplication of an infinity by a zero results in NaN.lMultiplication of an infinity by a finite value results in a signed infinity.The sign is determined by the rule stated above.lIn the remaining cases, where neither an infinity nor NaN is involved, the exact mathematical product is computed.A floating-point value set is then chosen:lIf the multiplication expression is FP-strict :lIf the type of the multiplication expression is float, then the float value set must be chosen.lIf the type of the multiplication expression is double, then the double value set must be chosen.lIf the multiplication expression is not FP-strict:lIf the type of the multiplication expression is float, then either the float value set or the float-extended-exponent value set may be chosen, at the whim of the implementation.lIf the type of the multiplication expression is double, then either the double value set or the double-extended-exponent value set may be chosen, at the whim of the implementation.Next, a value must be chosen from the chosen value set to represent the product.If the magnitude of the product is too large to represent, we say the operation overflows; the result is then an infinity of appropriate sign.Otherwise, the product is rounded to the nearest value in the chosen value set using IEEE 754 round-to-nearest mode.The Java programming language requires support of gradual underflow as defined by IEEE 754.Despite the fact that overflow, underflow, or loss of information may occur, evaluation of a multiplication operator * never throws a run-time exception.15.17.2 Division Operator /The binary / operator performs division, producing the quotient of its operands.The left-hand operand is the dividend and the right-hand operand is the divisor.Integer division rounds toward 0.That is, the quotient produced for operands n and d that are integers after binary numeric promotion is an integer value q whose magnitude is as large as possible while satisfying ; moreover, q is positive when and n and d have the same sign, but q is negative when and n and d have opposite signs.There is one special case that does not satisfy this rule: if the dividend is the negative integer of largest possible magnitude for its type, and the divisor is -1, then integer overflow occurs and the result is equal to the dividend.Despite the overflow, no exception is thrown in this case.On the other hand, if the value of the divisor in an integer division is 0, then an ArithmeticException is thrown.The result of a floating-point division is determined by the specification of IEEE arithmetic:lIf either operand is NaN, the result is NaN.lIf the result is not NaN, the sign of the result is positive if both operands have the same sign, negative if the operands have different signs.lDivision of an infinity by an infinity results in NaN.lDivision of an infinity by a finite value results in a signed infinity.The sign is determined by the rule stated above.lDivision of a finite value by an infinity results in a signed zero.The sign is determined by the rule stated above [ Pobierz całość w formacie PDF ]
