biginteger

I need to generate arbitrarily large random integers in the range 0 (inclusive) to n (exclusive). My initial thought was to call nextDouble and multiply by n, but once n gets to be larger than 2 53 , the results would no longer be uniformly distributed. BigInteger has the following constructor available: public BigInteger(int numBits, Random rnd) Constructs a randomly generated BigInteger, uniformly distributed over the range 0 to (2 numBits - 1), inclusive. How can this be used to get a random value in the range 0 - n, where n is not a power of 2? Thomas Pornin Use a loop: BigInteger

I have this piece of code, which is not working: BigInteger sum = BigInteger.valueOf(0); for(int i = 2; i < 5000; i++) { if (isPrim(i)) { sum.add(BigInteger.valueOf(i)); } } The sum variable is always 0. What am I doing wrong? MarkPowell BigInteger is immutable. The javadocs states that add() "[r]eturns a BigInteger whose value is (this + val)." Therefore, you can't change sum , you need to reassign the result of the add method to sum variable. sum = sum.add(BigInteger.valueOf(i)); sum = sum.add(BigInteger.valueOf(i)) The BigInteger class is immutable, hence you can't change its state. So

How would I go about doing arithmetic, + - / * % !, with arbitrarily large integers without using java.math.BigInteger ? For instance, the factorial of 90 returns 0 in Java. I would like to be able to solve that. Paŭlo Ebermann I think a programmer should have implemented his own bignum-library once, so welcome here. (Of course, later you'll get that BigInteger is better, and use this, but it is a valuable learning experience.) (You can follow the source code of this course life on github . Also, I remade this (a bit polished) into a 14-part blog series .) Creating a simple Big number class in