java - 接受计算器程序的输入

Question

我希望程序接受操作符号(+、-、*、/)作为输入。每当我这样做时，它就会抛出异常。任何人都可以帮我解决这个问题并使程序接受这些标志之一作为输入。

import java.lang.*;
import java.util.*;

public class Calculator
{
    private double solution;
    private static double x, y;
    private static char ops;

    public static interface Calculate
    {
        public abstract double operation(double x, double y);
    }

    public static class addition implements Calculate
    {
       public double operation(double x, double y){
         return(x+y);
       }
    }

    public static class subtraction implements Calculate
    {
       public double operation(double x, double y){
         return(x-y);
       }
    }

    public static class multiplication implements Calculate
    {
       public double operation(double x, double y){
         return(x*y);
       }
    }

    public static class division implements Calculate
    {
       public double operation(double x, double y){
         return(x/y);
       }
  }

    public void calc(int ops){
         Scanner operands = new Scanner(System.in);

         System.out.println("operand 1: ");
         x = operands.nextDouble();
         System.out.println("operand 2: ");
         y = operands.nextDouble();

         System.out.println("Solution: ");

         Calculate [] jumpTable = new Calculate[4];
         jumpTable['+'] = new addition();
         jumpTable['-'] = new subtraction();
         jumpTable['*'] = new multiplication();
         jumpTable['/'] = new division();

         solution = jumpTable[ops].operation(x, y);

         System.out.println(solution);
    }

    public static void main (String[] args)
    {
      System.out.println("What operation? ('+', '-', '*', '/')");
      System.out.println(" Enter 0 for Addition");
      System.out.println(" Enter 1 for Subtraction");
      System.out.println(" Enter 2 for Multiplication");
      System.out.println(" Enter 3 for Division");

      Scanner operation = new Scanner(System.in);
      ops = operation.next().charAt(0);

      Calculator calc = new Calculator();
      calc.calc(ops);
  }
}

错误是

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 43
at Calculator.calc(Calculator.java:54)
at Calculator.main(Calculator.java:76)

Answer 1

jumpTable['+']

将被转换为 + 符号的 ASCII 代码 (43)(它被转换为 char)，留下 0-4 范围内的数字范围。您可能想要使用实际的数字索引(或者确保您的数组可以包含 char 值集的最高数字表示形式，在本例中为 / 的 47)。

ASCII table :