Scanner:java.util.Scanner.next（未知源）问题

我制作了一个基本的计算器程序，我得到了一个例外：

java.util.InputMismatchException java.util.Scanner.next（未知源）

代码运行正常，但当出现异常时，它不允许用户使用

Scanner

进行输入。我做错了什么？我该如何修复它

package string;

import java.util.Scanner;
import java.lang.Exception;

public class Calculator {

double sum(double a,double b)
{
    double c =a+b;
    return c;
}

double subtract(double a,double b)
{
    double c= a-b;
    return c;
}

double multiply(double a,double b)
{
    double c=a*b;
    return c;
}

double divide(double a,double b)
{
    double c=a/b;
    return  c;
}


public static void main(String[] args) {
Calculator f= new Calculator();
int choice;
int z;

Scanner s1 =new Scanner(System.in);


do{
    try{

System.out.println("Welcome To Mini Calculator:  Which Function Do You Want To Use");
System.out.println("1.Addition");
System.out.println("2.Subtraction");
System.out.println("3.Multiplication");
System.out.println("4.Division");
System.out.println();
System.out.print("Please Enter Your Choice Number: ");
choice = s1.nextInt();

System.out.println();

switch(choice){
case 1: 
    System.out.print("Please Enter The First Number: ");
    double x= s1.nextDouble();
    System.out.println();
    System.out.print("Please Enter The Second Number: ");
    double y= s1.nextDouble();
    double u = f.sum(x,y);
    System.out.println();
    System.out.println("The Sum Of Two Numbers is: " + u);
    break;
case 2:
    System.out.print("Please Enter The First Number: ");
    double q= s1.nextDouble();
    System.out.println();
    System.out.print("Please Enter The Second Number: ");
    double w= s1.nextDouble();
    double i= f.subtract(q,w);
    System.out.println();
    System.out.println("The Substraction Of Two Numbers is: "+i );
    break;
case 3:
    System.out.print("Please Enter The First Number: ");
    double e= s1.nextDouble();
    System.out.println();
    System.out.print("Please Enter The Second Number: ");
    double r= s1.nextDouble();
    double o= f.multiply(e, r);
    System.out.println();
    System.out.println("The Multiplication Of Two Numbers " + o);
    break;
case 4:
    System.out.print("Please Enter The First Number: ");
    double t= s1.nextDouble();
    System.out.println();
    System.out.print("Please Enter The Second Number: ");
    double k= s1.nextDouble(); 
    double p= f.divide(t,k);
    System.out.println();
    System.out.println("The Divison of Two Numbers is: "+ p);
    break;
default:System.out.println(); 
    System.out.println("Please Enter a Valid Choice from 1 to 4");
}
}
catch(Exception e) {
    System.out.println("Input error: You have entered wrong input");
    System.out.println("Please restart the program");

    }
    System.out.println();
    System.out.println("Do You Want To perform Another Functionality?");
    System.out.println("Press 1 to Continue and Press 2 to Terminate The Program");
    z= s1.nextInt();  // Issue comes here. It runs fine without exception. When exception occurs in above code ,it doesn't take input and shows another exception
}
while(z==1);

System.out.println();
System.out.println("Thank You For Using Calculator");
s1.close();

}
}

---

当您输入错误的输入时，它会进入

catch

，但输入仍然在这里，因此

z=s1.nextInt（）引发另一个未捕获的异常，并导致崩溃

因此，您需要读取catch中的输入，以清除扫描仪：

} catch (Exception e) {
    System.out.println("Input error: You have entered wrong input");
    System.out.println("Please restart the program");
    s1.nextLine();
}


另外，你有很多代码重复，变量名没有任何意义，这与标准相比不是很好，我建议用这样的东西来代替你的整个
开关{…}

System.out.println();
System.out.print("Please Enter The First Number: ");
double numb1 = s1.nextDouble();
System.out.println();
System.out.print("Please Enter The Second Number: ");
double numb2 = s1.nextDouble();
double res;
String operation = "";

switch (choice) {
    case 1:
        res = f.sum(numb1, numb2);
        operation = "Sum";
        break;
    case 2:
        res = f.subtract(numb1, numb2);
        operation = "Substraction";
        break;
    case 3:
        res = f.multiply(numb1, numb2);
        operation = "Multiplication";
        break;
    case 4:
        res = f.divide(numb1, numb2);
        operation = "Divison";
        break;
    default:
        res = 0;
        System.out.println();
        System.out.println("Please Enter a Valid Choice from 1 to 4");
}

System.out.println();
System.out.println("The " + operation + " Of Two Numbers is: " + res);

您尝试了什么作为输入？我尝试了，它对我有效，因为引发异常的
nextFoo（）
方法没有使用输入，所以catch块中的
nextInt（）
调用被相同的错误输入阻塞。有关更多详细信息，请参阅。另外，一般情况下，不要对流控制使用异常，而是在尝试阅读之前使用
hasnetfoo（）
检查有效输入。azro-非常感谢您的澄清。现在有道理了。我在stackoverflow上读了15篇关于这类问题的帖子，但没有找到任何解释，只有解决方案。感谢您澄清问题背后的原因及其解决方案：）非常感谢。@Tarunjeethinghsalh没问题；）记住要避免代码重复，当您看到2-3行相同时，请只查找一次get；）同时考虑投票赞成/接受这个答案；）感谢您提供有关代码格式和维护良好标准的提示。我投了赞成票。我的名声不到15岁，因为我刚刚加入。我的投票记录在案，但不可见。从现在起，我将继续使用stackflow：）再次感谢好先生，@TarunjeetSinghSalh您可以接受答案，这比投票赞成要好；）