Simple Java addition calculator

Question

I made this simple addition calculator in Java and I'm wondering how I can improve it.

package com.craftxbox.main;
import java.util.Scanner;
public class Main {
 public static void main(String[] args){
 int inInt1;
 int inInt2;
 int outInt;
 @SuppressWarnings("resource")
 Scanner in = new Scanner(System.in);
 inInt1 = in.nextInt();
 inInt2 = in.nextInt();
 outInt = inInt1 + inInt2;
 System.out.println(outInt);
 }
}

• Caridorc: Craftbox, Welcome to Codereview! :)

Answer 1

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:

import java.util.InputMismatchException;
import java.util.Scanner;
public class Calculator
{
 static Scanner scanner;
 public static void main(String args[])
 {
 try
 {
 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;
 System.out.println(answer);
 }
 catch (InputMismatchException e)
 {
 System.out.println("Invalid input");
 }
 finally
 {
 scanner.close();
 }
}

}

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.

• Caridorc: Good answer, remember to: ¤ Declare and assign at the same time: double firstNum = Scanner ... ¤ Reduce the try block as much as possible

Answer 2

Declare and assign at the same time to avoid code-duplication:

 int inInt1 = in.nextInt();
 int inInt2 = in.nextInt();
 int outInt = inInt1 + inInt2;

Delete the three lines of declaration.

In fact, the whole program can be reduced to:

import java.util.Scanner;
public class Main {
 public static void main(String[] args){
 Scanner in = new Scanner(System.in);
 System.out.println( in.nextInt() + in.nextInt() );
 }
}

• craftxbox: Thanks, i still have one problem though, in is never closed

Answer 3

Since Java 7, the recommended way of closing Closeable resources such as Scanner is to use try-with-resources:

try (Scanner scanner = new Scanner(System.in)) {
 // ...
}
// no need for explicit scanner.close() here, 
// since the variable is scoped within the try statement and will be closed at the end

As mentioned in @Maxim's answer, you should also consider validating the inputs.