java如何修复无法解析从未使用过的符号和变量的错误

Question

我是java新手，这是我的第一个程序，我对这些错误感到非常困惑，并且到处寻找答案。请帮忙

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        Scanner myObj = new Scanner(System.in);

        System.out.println("Enter first number");
        String str1 = myObj.nextLine();

        System.out.println("Enter Operator");
        String op = myObj.nextLine();

        System.out.println("Enter second number");
        String str2 = myObj.nextLine();

        int num1 = Integer.parseInt(str1);
        int num2 = Integer.parseInt(str2);

        if (op.equals("+")) {
            int ans = (num1 + num2);
        } else if (op.equals("-")){
            int ans = (num1 - num2);
        }
        System.out.println(num1 + " " + op + " " + num2 + " = " + ans);
    }
}

然后它给了我这些错误，我用的是IntelliJ idea

Cannot resolve symbol 'ans'
Variable 'ans' is never used
Variable 'ans' is never used

Answer 1

Cannot resolve symbol 'ans'

在if之外声明ans

    int ans = 0; 
    if (op.equals("+")) {
        ans = (num1 + num2);
    } else if (op.equals("-")){
        ans = (num1 - num2);
    }
    System.out.println(num1 + " " + op + " " + num2 + " = " + ans);

否则，它在System.out.println中使用的行中永远不可见

Variable 'ans' is never used

Variable 'ans' is never used

在你的代码中，ans是在if-code块中声明的，在赋值之后，那些ans就不再被使用了，因为if中的代码块就在赋值之后结束