您如何检查用户输入的是字符串值而不是数字？

Question

I wrote a simple program that calculates the hypotenuse of a triangle when the user inputs side A and B. I have a while loop that prompts the user to enter a value greater than 0 if they do, but how do I check if the user enters a String value?

while (sideA<=0 || sideB<=0) {

What should I add so if the user enters a string value, the loop will also start?

Thanks

Answer 1

However you get your input (from command line, scanner or buffered reader) first parse it and try to store it in an integer variable. If its a string, then catch the exception and allow the user to enter the value again.

try 
{
   int sideA = Integer.parseInt(input);
} 
catch (NumberFormatException ex) 
{
  //Do something here to keep continuing the while loop

}

Answer 2

  Scanner input = new Scanner(System.in);

  // requesting user input
  System.out.println("Enter x and y : ");

  String x = input.next();
  String y = input.next();

  try {
     double d1 = Double.parseDouble(s1);
     double d2 = Double.parseDouble(s2);

     if(d1 > 0 && d2 > 0) {
        //Call for the hypotenuse method
        double z = hypotenuse(d1,d2);
     }
  } catch (NumberFormatException e) {
        System.out.println("Invalid Input!");
  }     

Answer 3

you can use the binary instanceof operator. it returns a boolean value in this manner:

if( myVariable instanceof String )
    //it's a string!
else
    //it's not a string

This approach can of course be used to check for other types as well. I recommend type checking your A and B variables as strings using instanceof and handle accordingly