JAVA.ARITH.OFLOW : Cast: int Computation to long (Java)

要旨

The result of an integer computation that might overflow is cast into long, with possible loss of precision.

Floating point operations are by nature approximated. This can introduce bugs when precise, mathematical properties are expected from inherently imprecise floating point computations. Moreover, computations that might lose precision or overflow, whose result is stored in a larger type, are suspicious since, by computing on the larger type from the beginning, one could avoid approximations and overflows.

プロパティ

WARNING_FILTER += discard class="Cast: int Computation to long (Java)"

例

public class MillisecondsInDays {
  public static void main(String[] args) {
    int days = Integer.parseInt(args[0]);
    long milliseconds = days * 24 * 60 * 60 * 1000; // "Cast: int Computation to long (Java)" warning issued here

    System.out.printf("Inside %d days there are %d milliseconds", days, milliseconds);
  }
}

The computation days * 24 * 60 * 60 * 1000 is performed on integers and then stored into a long. As a consequence, the extra space allowed by a long value is not exploited and the computation will overflow if days is larger than 24.

To avoid this problem, perform the computation with long values, so that the entire long space is available. Overflow will only occur for very large values of days.

public class MillisecondsInDays {
  public static void main(String[] args) {
    int days = Integer.parseInt(args[0]);
    long milliseconds = days * 24L * 60 * 60 * 1000;

    System.out.printf("Inside %d days there are %d milliseconds", days, milliseconds);
  }
}

解決法

If a large type for the result of a computation is desired, compute from the beginning on that type instead of applying a type conversion at the end of the computation.

関連のある設定ファイルパラメータ

設定ファイルの以下のパラメータがこのワーニングクラスのチェックに影響します。

• REPORT_SIMILAR_WARNINGS
• WARNING_FILTER