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Programs must not allow mathematical operations to exceed the integer ranges provided by their primitive integer data types. According to the Java Language Specification (JLS), §4.2.2, "Integer Operations,"

The built-in integer operators do not indicate overflow or underflow in any way. Integer operators can throw a NullPointerException if unboxing conversion of a null reference is required. Other than that, the only integer operators that can throw an exception are the integer divide operator / and the integer remainder operator %, which throw an ArithmeticException if the right-hand operand is zero, and the increment and decrement operators ++ and -- which can throw an OutOfMemoryError if boxing conversion is required and there is not sufficient memory available to perform the conversion.

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• BigInteger. Convert the inputs into objects of type BigInteger and perform all arithmetic using BigInteger methods. Type BigInteger is the standard arbitrary-precision integer type provided by the Java standard libraries. The arithmetic operations implemented as methods of this type cannot overflow; instead, they produce the numerically correct result. As a consequenceConsequently, compliant code only performs a single range check just before converting the final result to the original smaller type and throwing an ArithmeticException if the final result is outside the range of the original smaller type.

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This compliant solution uses the safeAdd() and safeMultiply() methods defined in the Pre-condition testing Condition Testing section to perform secure integral operations or throw ArithmeticException on overflow.

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• The number and order of accesses to itemsInInventory remains remain unchanged from the noncompliant code example.
• All operations on the value of itemsInInventory are performed on a temporary local copy of its value.
• The overflow check in this example is performed in inline code , rather than encapsulated in a method call. This is an acceptable alternative implementation. The choice of method call versus inline code should be made according to your organization's standards and needs.

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