An integer multiplication that is assigned to a variable of type long or returned from a method with return type long may cause unexpected arithmetic overflow.

Casting to type long before multiplying reduces the risk of arithmetic overflow.

In the following example, the multiplication expression assigned to j causes overflow and results in the value -1651507200 instead of 4000000000000000000.

In the following example, the assignment to k correctly avoids overflow by casting one of the operands to type long.

J. Bloch and N. Gafter, Java Puzzlers: Traps, Pitfalls, and Corner Cases, Puzzle 3. Addison-Wesley, 2005.

Java Language Specification: Multiplication Operator.

SEI CERT Oracle Coding Standard for Java: NUM00-J. Detect or prevent integer overflow.