Switch to BigInteger if necessary

Question

I am reading a text file which contains numbers in the range [1, 10^100]. I am then performing a sequence of arithmetic operations on each number. I would like to use a BigInteger only if the number is out of the int/long range. One approach would be to count how many digits there are in the string and switch to BigInteger if there are too many. Otherwise I'd just use primitive arithmetic as it is faster. Is there a better way?

Is there any reason why Java could not do this automatically i.e. switch to BigInteger if an int was too small? This way we would not have to worry about overflows.

Answer 1

I suspect the decision to use primitive values for integers and reals (done for performance reasons) made that option not possible. Note that Python and Ruby both do what you ask.

In this case it may be more work to handle the smaller special case than it is worth (you need some custom class to handle the two cases), and you should just use BigInteger.

Answer 2

Is there any reason why Java could not do this automatically i.e. switch to BigInteger if an int was too small?

Because that is a higher level programming behavior than what Java currently is. The language is not even aware of the BigInteger class and what it does (i.e. it's not in JLS). It's only aware of Integer (among other things) for boxing and unboxing purposes.

Speaking of boxing/unboxing, an int is a primitive type; BigInteger is a reference type. You can't have a variable that can hold values of both types.