Scanner.nextInt（）挣扎

Question

I made a simple text-based calculator, and it all runs fine except for my method which handles getting the user input. Even though I create a new instance of my class in the main method, and use that instance to call the input method, I still get the compiler error that I'm referencing nextInt() from a static context. Enlighten me, please. My main method is as follows:

  public static void main (String[] args) {
    CalculatorTextVersion calculator = new CalculatorTextVersion();
    Scanner scanner = new Scanner(System.in);
    calculator.getCalculation();
  }

And the getCalculation method is as follows:

  public void getCalculation() {

    while (calculating = true) {

      System.out.print("First number: ");
      first = Scanner.nextInt();
      System.out.print("Second number: ");
      second = Scanner.nextInt();
      System.out.println("Choose an operation: | 1. Add | 2. Subtract | 3. Multiply | 4. Divide |:");
      opcode = Scanner.nextInt();
      calculate(first, second, opcode);
      getSymbol(opcode);
      System.out.println(first + opcode + second + " equals " + result + "." );
      System.out.print("Continue? Y/N:");
      yesNo = Scanner.next();

      if (yesNo == "Y" | yesNo == "Yes" | yesNo == "yes") {
        calculating = true;
      }

      if (yesNo == "N" | yesNo == "No" | yesNo == "no") {
        calculating = false;
      }
    }
  }

Note: all variables, methods, and imports are fine, I just didn't include them as they weren't part of the problem.

EDIT: Using the oft-suggested technique of creating an instance variable for the scanner got past the compiler, but generated null pointer errors upon running.

EDIT 2: Problem solved, I tried the idea of creating a new scanner in the only method it was needed, worked like a charm. Thanks!

Answer 1

This is the simplest/best solution so I removed the others.

public class YourClass
{
    public static void main(String[] args)
    {
        //Scanner scanner is now declared in your CalculatorTextVersion
        //CalculatorTextVersion() class in its constructor

        //Scanner scanner = new Scanner(System.in);

        CalculatorTextVersion calculator = new CalculatorTextVersion();
        calculator.getCalculation();
    }
}

---

import java.util.Scanner;

public static class CalculatorTextVersion
{
    Scanner scanner;

    public CalculatorTextVersion() {
        scanner = new Scanner(System.in);
    }
    public void getCalculation()
    {
        scanner.nextInt();
    }
}

Answer 2

I guess you need to move

Scanner scanner = new Scanner(System.in);

into the CalculatorTextVersion class.

Answer 3

You're going to need to do this:

public Scanner scanner = new Scanner(System.in);

in the main method.

This publicizes the scanner for use in the getCalculation() method.

Good Luck!