How to create a BinaryOperator to add up BigInteger

Question

I want to create a BinaryOperator<BigInteger> biOp in order to add up BigInteger values. For example, I will have a huge list or array of different BigInteger values and I want to add them all up using a loop and the biOp.

The result for e.g. two values should look something like this:

System.out.println(biOp.apply(BigInteger.ONE, BigInteger.ONE));
// outputs 2

How do I create or initialize biOp properly?

Answer 1

The simplest way is to use a method reference to BigInteger::add:

BinaryOperator<BigInteger> binOp = BigInteger::add;

This works because when you use the class name to create a method reference to an instance method (i.e. not a static method), the apply method will take an extra parameter for the instance to call the method on. So although the add method takes one BigInteger parameter, this method reference takes two BigInteger parameters.