try{
int poop = Integer.parseInt("Not a number");

//All code happening in the try{} AFTER the parsing of the int will onloy execute if it worked, so if it was a number.

}catch(Exception e){
//This code will only execute if there was an exception. As I don't remember the exact Exception name, I just used Exception.
//Which is like a joker as it will detect all exceptions. (It's probs something like InvalidNumberException)

//Use this to print the error to the console (which you probs don't want but meh).
e.printStackTrace();
//If you don't use that line the error will still occur but not spam the console.

//Now tell the player their numer was invalid:
player.sendMessage("Not a number smartass");
}