Extraction

Extraction in Programming Languages is where you extract part of a method or function out in to its own method or function.

Example before extraction:

int filterNumber(int number){
  if(number % 2){
    return number;
  }

  return 0;
}

int calculate(int bottom, int top){
  if (top > bottom){
    int sum = 0;

    for (int number = bottom; number <= top; number++){
      sum += filterNumber(number);
    }
    return sum;
  } else {
    return 0;
  }
}

Example after extraction: