Question

In java, I know the data type of the result of an arithmetic calculation depends on the data types of the numbers involved in the calculation.
For example,

1. int + int = int

2. long/double=double

a. But I can’t find any references which can give me all these rules. Could someone help me?

b. How to avoid over flow in arithmetic calculation? For example, the results of 2 long may not fit into a long anymore…

Thanks a lot.

Answer 1

a. These rules are called numeric promotion rules and are specified in Java Language Specification, §5.6.2 (currently).

b. There are two generally accepted method for dealing with overflows.

The first method, a post-check, where you do an operation, say addition and then check that the result is greater than either of the operands. For example:

int c = a + b;

if( c<a) {  // assuming a>=0 and b>=0
   // overflow happened
}

The second method, is a pre-check, where you basically try to avoid the overflow from happening in the first place. Example:

if( a > Integer.MAX_INTERGER - b ) {
   // overflow happened
}