преобразовать строку в арифметическую операцию

Question

Я делаю программу, которая представляет студенту математическую викторину. У меня возникли проблемы с выяснением того, как взять тип проблемы ввода и превратить эту строку в арифметический оператор. Вот метод для этой части кода. Пожалуйста, спасибо!

public static String getUserChoice(String choice) { 
    Scanner in = new Scanner(System.in); 

    System.out.println("Please enter the symbol that corresponds to one of the following problems\n" 
      + "Addition (+)\n Subtraction (-)\n or Multiplication (*): "); 
    choice = in.next(); 
     if ("+".equals(choice)){ 
      return +; 
     } 
     } 
    return choice; 

Update Вот весь код, если это помогает увидеть, что я делаю.

public static void main(String[] args) { 
    int digit = 0; 
    int random = 0; 

    String result1 = getUserChoice(""); 

    digit = getNumberofDigit1(digit); 

    int number1 = getRandomNumber1(digit); 
    int number2 = getRandomNumber2(digit); 

    System.out.println(number1 + result1 + number2); 
    getCorrectAnswer(number1, result1, number2); 

} 

public static String getUserChoice(String choice) { 
    Scanner in = new Scanner(System.in); 

    System.out.println("Please enter the symbol that corresponds to one of the following problems\n" 
      + "Addition (+)\n Subtraction (-)\n or Multiplication (*): "); 
    choice = in.next(); 


    return choice; 
} 

public static int getNumberofDigit1(int digit) { 
    Scanner in = new Scanner(System.in); 

    System.out.println("Enter a 1 for problems with one digit, or a 2 for two-digit problems: "); 
    digit = in.nextInt(); 

    return digit; 
} 


public static int getRandomNumber1(int numbers) { 
     int random = 0; 
      if (numbers == 1) { 
       random = (int) (1 + Math.random() * 9); 
      } else if (numbers == 2) { 
       random = (int) (10 + Math.random() * 90); 
      } 
     return random; 
} 

public static int getRandomNumber2(int numbers) { 
    int random2 = 0; 
      if (numbers == 1) { 
       random2 = (int) (1 + Math.random() * 9); 
      } else if (numbers == 2) { 
       random2 = (int) (10 + Math.random() * 90); 
      } 
      return random2; 
} 
public static void getCorrectAnswer(int number1, String result1, int number2) { 
} 

public static void getUserAnswer() { 
    Scanner in = new Scanner(System.in); 

} 

public static void CheckandDisplayResult() { 
} 

Answer 1

Во-первых, я хочу показать вам, как проверить, не хочет ли он того, что вы хотите.

Вы всегда можете проверить, чтобы убедиться, что это строка или int или w/e, выполнив следующее.

Scanner scan = new Scanner(System.in); 
while(scan.hasNext()) { 
    if(scan.hasNextInt()) { 
    int response = scan.nextInt(); 
    } 
} 

Вот код того, что вы хотите сделать.

import java.util.Random; 
import java.util.Scanner; 

public class Main { 

    static Scanner in = new Scanner(System.in); 

    public static void main(String[] args) { 
     // Math Quiz v1.0 // 
     String printme = "Please choose the quiz type:\n\n" 
       + "(1) Addition\n" 
       + "(2) Subtraction\n" 
       + "(3) Multiplication\n" 
       + "(4) Division\n" 
       + "(5) Modulus\n\n\n"; 

     System.out.println(printme); 

     int reponse = in.nextInt(); 

     // Setup // 
     int a = new Random().nextInt(100); 
     int b = new Random().nextInt(100); 

     int answer = -1; 

     switch(reponse) { 
      case 1: 
       System.out.println("What is " + a + " + " + b + "?"); 
       answer = in.nextInt(); 
       if(answer == a + b) { 
        System.out.println("Your right!"); 
       } else { 
        System.out.println("You fail!"); 
       } 
       break; 
      case 2: 
       System.out.println("What is " + a + " - " + b + "?"); 
       answer = in.nextInt(); 
       if(answer == a - b) { 
        System.out.println("Your right!"); 
       } else { 
        System.out.println("You fail!"); 
       } 
       break; 
      case 3: 
       System.out.println("What is " + a + " * " + b + "?"); 
       answer = in.nextInt(); 
       if(answer == a * b) { 
        System.out.println("Your right!"); 
       } else { 
        System.out.println("You fail!"); 
       } 
       break; 
      case 4: 
       System.out.println("What is " + a + "/" + b + "?"); 
       answer = in.nextInt(); 
       if(answer == a/b) { 
        System.out.println("Your right!"); 
       } else { 
        System.out.println("You fail!"); 
       } 
       break; 
      case 5: 
       System.out.println("What is " + a + " % " + b + "?"); 
       answer = in.nextInt(); 
       if(answer == a % b) { 
        System.out.println("Your right!"); 
       } else { 
        System.out.println("You fail!"); 
       } 
       break; 
      default: 
       System.out.println("Error, enter an integer between 1 & 5."); 
       break; 
     } 
    } 
} 

Answer 2

вот один подход к вашей проблеме:

private static Scanner input; 
public static void main(String[] args) { 
    input = new Scanner(System.in); 
    final String result1 = getUserChoice(); 
    final int digit = getNumberofDigit1(); 
    final int number1 = getRandomNumber(digit); 
    final int number2 = getRandomNumber(digit); 
    System.out.println(number1 + result1 + number2); 
    final int userAnswer = input.nextInt(); 
    final int correctAnswer = getCorrectAnswer(number1, result1, number2); 
    System.out.println((userAnswer == correctAnswer) ? "Ok" : ("Wrong, right is: " + correctAnswer)); 
    input.close(); 
} 

public static String getUserChoice() { 
    System.out.println("Please enter the symbol that corresponds to one of the following problems\n" + "Addition (+)\n Subtraction (-)\n or Multiplication (*): "); 
    return input.next(); 
} 

public static int getNumberofDigit1() { 
    System.out.println("Enter a 1 for problems with one digit, or a 2 for two-digit problems: "); 
    return input.nextInt(); 
} 

public static int getRandomNumber(final int numbers) { 
    return (int) ((numbers == 1) ? (1 + Math.random() * 9) : (10 + Math.random() * 90)); 
} 

public static int getCorrectAnswer(final int number1, final String result1, final int number2) { 
    if ("+".equals(result1)) 
     return number1+number2; 
    else if ("-".equals(result1)) 
     return number1-number2; 
    else if ("*".equals(result1)) 
     return number1*number2; 
    return -1; 
} 

и здесь немного другая getCorrectAnswer часть:

public interface IMyOperator { 
    public int operation(final int a, final int b); 
}; 

static class classSum implements IMyOperator { 
    public int operation(final int a, final int b) { 
     return a+b; 
    } 
} 

static class classSub implements IMyOperator { 
    public int operation(final int a, final int b) { 
     return a-b; 
    } 
} 

static class classMul implements IMyOperator { 
    public int operation(final int a, final int b) { 
     return a*b; 
    } 
} 

final static HashMap<String, IMyOperator> operators = new HashMap<String, IMyOperator>(3) {{ 
    put("+", new classSum()); 
    put("-", new classSub()); 
    put("*", new classMul()); 
}}; 

public static int getCorrectAnswer(final int number1, final String result1, final int number2) { 
    return operators.get(result1).operation(number1, number2); 
}