java - 为什么我的 java 计算器代码不工作？

Question

package calculator;

import java.util.Scanner;

/**
 * @author zhoushi15
 */
public class Calculator {
    public static double num1;
    public static double num2;
    public static String opp;
    /**
     * @param args the command line arguments
     */
    public static double sum;

    public static void main(String[] args) {
        // TODO code application logic here
        boolean quit;
        String calculator;
        String exp;
        System.out.print("Welcome to the AP Computer Science calculator!!");
        Scanner input = new Scanner(System.in);
        boolean calc = false;
        while (calc == false) {
            System.out.print("Enter an expression, or quit to exit: ");
            exp = input.nextLine();
            if (exp.equalsIgnoreCase("quit")) {
                System.out.println("Thanks for stopping by!");
                calc = true;
            } else {
                token(exp);
                System.out.println(exp + "=" + sum);
            }
        }
    }

    public static void token(String x) {
        Scanner jz = new Scanner(x);
        if (jz.hasNextDouble()) {
            if (jz.hasNextDouble()) {
                num1 = jz.nextDouble();
            } else {
                System.out.println("error! It is not a number.");
            }
            if (jz.hasNext()) {
                opp = jz.next();
            }
            if (jz.hasNextDouble()) {
                num2 = jz.nextDouble();
            }
        } else if (jz.hasNext()) {
            if (jz.hasNext()) {
                opp = jz.next();
            }
            if (jz.hasNextDouble()) {
                num1 = jz.nextDouble();
            }
        }
    }

    public static void opp(double num1, String opp, double num2) {
        if (opp.equals("+")) {
            sum = num1 + num2;
        } else if (opp.equals("-")) {
            sum = num1 - num2;
        } else if (opp.equals("*")) {
            sum = num1 + num2;
        } else if (opp.equals("/")) {
            sum = num1 / num2;
        }
    }

    public static void opp2(String opp, double num1) {
        if (opp.equals("|")) {
            sum = Math.abs(num1);
        } else if (opp.equals("v")) {
            sum = Math.sqrt(num1);
        } else if (opp.equals("~")) {
            sum = Math.round(num1);
        } else if (opp.equals("s")) {
            sum = Math.sin(num1);
        } else if (opp.equals("c")) {
            sum = Math.cos(num1);
        } else if (opp.equals("t")) {
            sum = Math.tan(num1);
        }
    }
}

我的代码不是给出答案。例如，我的输入是4+5，那么输出是0.0，但我找不到问题出在哪里以及如何解决它。

Answer 1

看看您的 main 方法，您从未给变量 sum 赋值或调用执行此操作的方法。因此，您的计算器始终将结果打印为 0.0，这是 double 的默认初始化值。 opp 和 opp2 不会自动使用，您需要实际调用它们。