Solidity Function Overload

Solidity does not support optional parameters, but what it does support is method overrides. Just like in Java you can declare a function multiple times as long as the arity and/or types are different.

Example I tried on remix:

pragma solidity ^0.4.18;

contract Overload {
  function calculate (uint _a, uint _b) public pure returns (uint) {
    return _a + _b;
  }
  function calculate (uint _a, uint _b, uint _c) public pure returns (uint) {
    return _a + _b + _c;
  }
}

Here's a silly example with an internal function that both use, just to demonstrate reusable functionality:

pragma solidity ^0.4.18;

contract Overload {
  function calculate (uint _a, uint _b) public pure returns (uint) {
    return addTwo(_a, _b);
  }
  function calculate (uint _a, uint _b, uint _c) public pure returns (uint) {
    return addTwo(addTwo(_a, _b), _c);
  }
  function addTwo(uint _a, uint _b) internal pure returns (uint) {
    return _a + _b;
  }
}