You have written some good code, but what if the user does not enter a number, but makes a mistakes? You can, and should, catch that error. What about this:
public class Calculator
static Scanner scanner;
public static void main(String args)
scanner = new Scanner(System.in);
double firstNum, secondNum, answer;
System.out.println("Enter your first number: ");
firstNum = scanner.nextDouble();
System.out.println("Enter your second number: ");
secondNum = scanner.nextDouble();
answer = firstNum + secondNum;
catch (InputMismatchException e)
I think a try - catch - finally is a great way of getting user input. This way your problem of the Scanner not being closed, is solved. If this is a little over you head right now, don't worry. It does what it says: we "try" the code in the try block, but if something goes wrong, in this case a "Inputmismatchexception", which means if the user inputs something wrong, we catch it and we display a message saying something went wrong.
Note that I have also changed the variable names. By reading the name, you should immediately know what it is and so names like firstNum and answer are a little better than inInt1 and stuff.
Hope you're still with me. If something is not clear, please feel free to ask some more questions. I myself am a beginner to Java and programming in general and this is the first question I answered.