我有办法重新输入错误的输入吗？

Question

I am making a basic calculator, where it does addition, multiplication, etc. It first checks the type of operation it is eg, 1 is for addition, 2 for multiplication and so on. If it detects that the operation type input is invalid, it just simply tells me in the console an error. Is there any method I can use to detect the method, and then re-enter the input?

public void printCheck() throws ArithmeticException{

        if (op == 2) {
            System.out.println("You have chosen addition");
        }

        else if (op == 3) {
            System.out.println("You have chosen subtraction");
        }

        else if (op == 4) {
            System.out.println("You have chosen multiplication");
        }

        else if (op == 5) {
            System.out.println("You have chosen division");
        }

        else {
            throw new ArithmeticException("Entered an invalid operation"); 
        }

            try {
                a.op(0);
            }

            catch(ArithmeticException e){
                System.out.println("You have entered an invalid operation");
            }

Answer 1

You may repeat the input of the operation code until it is valid.

I don't recommend using exceptions here because it's a common and well known case that the user gives an invalid input. Instead you should create a simple method isValidOperationCode which checks the input. For improved readability I have removed the global variable op and turned it into a local variable which gets passed as parameter into the methods which need it.

Example:

int op;
do {
    op = askUserForOperation();
    printCheckOperation(op);
} while (!isValidOperationCode(op));

with a modified printCheckOperation method

    ...
} else if (op == 5) {
    System.out.println("You have chosen division");
} else {
    System.out.println("Entered an invalid operation"); 
}

and the new method

private boolean isValidOperationCode(int op) {
    return 2 <= op && op <= 5;
}

Answer 2

I'm Sorry i couldn't be more elaborate since I'm using a mobile phone to answer to this question. I hope this answer helps.

  public void printCheck(){
    while(true){
     if(op<2 || op>5){
           enterNewOp();
     }
     else {
            switch(op) {
                  case 2:
                  System.out.println("You have select addition");
                  case 3:
                  System...
                  case 4:
                   ......
            }
     break;
     }
    }
   }