java - 即使捕获到异常，执行也会终止

Question

我正在运行一个简单的计算器应用程序来学习 Java 的异常处理。我设置了两个要处理的异常:InputMismatchException 和 ArithmeticException(除以零)。

ArithmeticException 被处理并且 do-while 循环继续。但是在捕获InputMismatchException之后，执行终止而不是继续循环。

代码:

do {
  result = 0;
  System.out.println("Enter the expression to calculate: (eg: 4 + 5) \n");
  try {
    num1 = input.nextInt();
    op = input.next().charAt(0);
    num2 = input.nextInt();
    result = a.Calc(num1, op, num2);             //Calc function to calculate
    System.out.println("= " + result);
  } catch (InputMismatchException e) {
     System.err.println("Please space out the expression");
  } catch (ArithmeticException e) {
     System.err.println("Cannot divide by zero");
  }
  System.out.println("Do you want to try again? (Y to retry)");
  OP = input.next().charAt(0);
} while (OP == 'Y' || OP == 'y');

输出:

Enter the expression to calculate: (eg: 4 + 5)
4 / 0
Cannot divide by zero                  //Exception handled
Do you want to try again? (Y to retry)
Y                                      //Do-while continues

Enter the question to calculate: (eg: 4 + 5)
4+5
Please space out the expression        //Exception handled
Do you want to try again? (Y to retry) //Rest of the code is executed
                                       //But the execution also terminates

预期:在InputMismatchException之后继续执行

这是正确的做法吗？

Answer 1

InputMismatchException 是由调用 nextInt() 引起的，因为下一个标记是 4+5。

失败的调用不会消耗 token 。

这意味着 OP = input.next().charAt(0) 设置 OP = '4'，如果您，这一点应该非常明显调试了代码。请参阅What is a debugger and how can it help me diagnose problems?和 How to debug small programs .

您需要丢弃失败的 token ，例如通过在 catch 子句中调用 nextLine() :

} catch (InputMismatchException e) {
    System.err.println("Please space out the expression");
    input.nextLine(); // Discard input(s)
} ...