java - 如何在我的java计算器中返回int？

Question

如果我的标题不够具体，我很抱歉。我正在尝试创建一个计算器。您输入:“手术”“数字1”“数字2”

你就会得到答案。

目前，我从以下代码中收到以下错误:

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
    This method must return a result of type int

    at LessonOne.Main.calcu(Main.java:17)
    at LessonOne.Main.main(Main.java:13) 

我的输入是“+”、“5”、“5”

请告诉我我做错了什么。我花了几个小时编辑这个，这是我想出的最好的。我完全陷入困境。

package LessonOne;

import java.util.Scanner;

public class Main { 

    public static Scanner s = new Scanner(System.in); //<-- DO NOT TOUCH

    public static void main(String[] args) {
        String oper = getStr(); //Enter your operator
        int numberOne = getInteger(); //Enter your first number
        int numberTwo = getInteger(); //Enter your second number
        int total = calcu(oper, numberOne, numberTwo); //Perform calculation
        System.out.println(total); //Print the total
    }   

    static int calcu(String oper, int numberOne, int numberTwo) {
        if (oper.equals('+')) {
            int total = add(numberOne, numberTwo);
            return total;
        } else if (oper.equals('-')) {
            int total = sub(numberOne, numberTwo);
            return total;
        } else if (oper.equals('*')) {
            int total = multi(numberOne, numberTwo);
            return total;
        } else if (oper.equals('/')) {
            int total = div(numberOne, numberTwo);
            return total;
        }

    }

    static int add(int numberOne, int numberTwo) {
        return int total = numberOne + numberTwo;


    }

    static int multi(int numberOne, int numberTwo) {
        return int total = numberOne * numberTwo;

    }

    static int sub(int numberOne, int numberTwo) {
        return int total = numberOne - numberTwo;

    }

    static int div(int numberOne, int numberTwo) {
        return int total = numberOne / numberTwo;
    }

    public static String getStr() {//<-- DO NOT TOUCH
        return s.nextLine();//<-- DO NOT TOUCH
    }//<-- DO NOT TOUCH

    public static int getInteger() { //<-- DO NOT TOUCH
        return s.nextInt(); //<-- DO NOT TOUCH
    } //<-- DO NOT TOUCH

}

Answer 1

问题是，如果操作数不是您正在测试的操作数之一，您的方法 calcu() 不会返回任何内容。

在最后一次测试后添加返回语句，或者引发异常。我建议抛出未经检查的异常:

throw new IllegalArgumentException("Unknown operation " + oper);