Is it possible to call the main(String[] args) after catching an exception?

Question

I'm working on a Serpinski triangle program that asks the user for the levels of triangles to draw. In the interests of idiot-proofing my program, I put this in:

Scanner input= new Scanner(System.in);
System.out.println(msg);
try {
    level= input.nextInt();
} catch (Exception e) {
    System.out.print(warning);
    //restart main method
}

Is it possible, if the user punches in a letter or symbol, to restart the main method after the exception has been caught?

Answer 1

You can prevent the Scanner from throwing InputMismatchException by using hasNextInt():

if (input.hasNextInt()) {
   level = input.nextInt();
   ...
}

This is an often forgotten fact: you can always prevent a Scanner from throwing InputMismatchException on nextXXX() by first ensuring hasNextXXX().

But to answer your question, yes, you can invoke main(String[]) just like any other method.

See also

• (Java) Opinion: Preventing Exceptions vs. Catching Exceptions
• How do I keep a scanner from throwing exceptions when the wrong type is entered? (java)

---

Note: to use hasNextXXX() in a loop, you have to skip past the "garbage" input that causes it to return false. You can do this by, say, calling and discarding nextLine().

    Scanner sc = new Scanner(System.in);
    while (!sc.hasNextInt()) {
        System.out.println("int, please!");
        sc.nextLine(); // discard!
    }
    int i = sc.nextInt(); // guaranteed not to throw InputMismatchException

Answer 2

Well, you can call it recursively: main(args), but you'd better use a while loop.

Answer 3

You much better want to do this:

boolean loop = true;
Scanner input= new Scanner(System.in);
System.out.println(msg);
do{
    try {
        level= input.nextInt();
        loop = false;
    } catch (Exception e) {
        System.out.print(warning);
        //restart main method
        loop = true;
    }
while(loop);