java - 在java计算器中验证用户输入的问题

Question

因此，我正在用 Java 编写计算器代码作为作业，我想在最后包含一个 else 语句，如果用户没有输入有效的运算符，则会收到错误消息。问题是，即使我输入有效的运算符，它也会打印结果，然后打印 else 错误消息。任何帮助，将不胜感激。

public class Main {

    public static void main(String[] args){

        Scanner inputi=new Scanner(System.in);
        double num1,num2;
        char operator;

        System.out.println("Please enter the first number: ");
        num1=inputi.nextDouble();
        System.out.println("Please enter the second number: ");
        num2=inputi.nextDouble();

        Scanner oper=new Scanner(System.in);
        System.out.println("Please enter the operator, the operators are +,-,*,/,%");
        operator = oper.next().charAt(0);

        if(operator== '+') { 
            System.out.println("The sum of these numbers is: "+(num1+num2));
        }
        if(operator=='-') {
            System.out.println("The diff of these numbers is: "+ (num1-num2));       
        }
        if(operator=='*') {
            System.out.println("The result of this multiplication is: "+(num1*num2));
        }
        if(operator=='/') {
            System.out.println("The division is: "+(num1/num2));
        }
        if(operator=='%') {
            System.out.println("The module is: "+(num1%num2));    
        }             
        else {
            System.out.println("Please just pick an operator..");

        }
   }

}

Answer 1

我建议使用 switch 来代替:

     switch (operator) {
        case '+':
            System.out.println("+");
            break;
        case '-':
            System.out.println("-");
            break;
    /* Other operators */
        default:
            System.out.println("Please just pick an operator..");
    }