How can I calculate modulo of a large number in String format in java

Question

I am trying to calculate an expression in java which is in String i.e 99999999999999999^99999999999999999 I want to calculate this number modulo 1000000007. I currently trying to store the big numbers as double but taking modulo with double gives me NaN. Can somebody help ?

Answer 1

You can use BigInteger and modPow(BigInteger, BigInteger) like

BigInteger m = new BigInteger("1000000007");
BigInteger a = new BigInteger("99999999999999999");
BigInteger b = new BigInteger("99999999999999999");
BigInteger answer = a.modPow(b, m);
System.out.println(answer);

which gives

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