掃描儀：java.util.Scanner.next（未知來源）問題

Question

我做了一個簡單的計算器程序，我得到這個異常：

java.util.InputMismatchException java.util.Scanner中.next（Unknown Source）

代碼運行的很好，但是當發生異常時，它不允許用戶使用Scanner進行輸入。我做錯了什麼，我該如何解決它？

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(); 

} 
} 

Answer 1

當你輸入一個錯誤的輸入，它會在catch但投入仍然在這裏，所以z= s1.nextInt();拋出未釣到另一個例外，它崩潰

所以，你需要讀取輸入中漁獲物中，以清除掃描儀：

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

---

而且，你有很多的代碼重複的，和變量名，這意味着什麼，這不是很好COMPAR e標準，我會建議這樣的事情來取代你的整個switch{ ... }

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);