错误：（18，29）java:'；'预期+错误：（18，39）java:不是语句

Question

它应该问1号、2号和操作员的问题是什么

package com.company;

import java.util.Scanner;


public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter number 1: ");
        int operand1 = scan.nextInt();
        System.out.print("Enter operator: ");
        String operator = new Scanner(System.in).nextLine();

        System.out.print("Enter number 2: ");
        int operand2 =  scan.nextInt();
        if (operator == "+") {
            return int.class(operand1 + operand2);
        }
        else if (operator == "-") {
            return int.class(operand1 - operand2);
        }
        else if (operator == "*") {
            return int.class(operand1 * operand2);
        }
        else {
            return "error...";
        }
    }

}
// Error:(18, 29) java: ';' expected
// Error:(18, 39) java: not a statement

错误 错误：（18，29）java:'；'预期+错误：（18，39）java:不是语句

Answer 1

有几个问题：

1. main被声明为void，所以你不应该return任何东西
2. 字符串比较是用Java中的equals进行的，而不是==
3. 您可能希望显示结果，而不是返回结果：使用System.out.print而不是return
4. 如上所述：我不确定你想通过用int.class(...)包装算术运算来做什么，但它没有做你认为它在做的事情

请参阅下面的更正（或直接运行here）：

import java.util.Scanner;   

public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter number 1: ");
        int operand1 = scan.nextInt();
        System.out.print("Enter operator: ");
        String operator = new Scanner(System.in).nextLine();

        System.out.print("Enter number 2: ");
        int operand2 =  scan.nextInt();
        if (operator.equals("+")) {
            System.out.print(operand1 + operand2);
        } else if (operator.equals("-")) {
            System.out.print(operand1 - operand2);
        } else if (operator.equals("*")) {
            System.out.print(operand1 * operand2);
        } else {
            System.out.print("error: unknown Operation: " + operator);
        }
    }

}