Prevent user from entering whitespace in Java

Question

I want the user to only enter his age. So I did this program :

Scanner keyb = new Scanner(System.in);  
int age;

while(!keyb.hasNextInt())
{
    keyb.next();
    System.out.println("How old are you ?");
}

age = keyb.nextInt();
System.out.println("you are" + age + "years old");

I found how to prevent user from using string by using the while loop with keyb.hasNextInt(), but how to prevent him from using the whitespace or from entering more input than his age ?

For example I want to prevent this kind of typing "12 m" or "12 12"

Also, how can I clear all existing data in the buffer ? I'm facing an infinite loop when I try to use this :

while(keyb.hasNext())
  keyb.next();

Answer 1

You want to get the whole line. Use nextLine and check that for digits e.g.

String possibleAge = "";
do {
    System.out.println("How old are you ?");
    possibleAge = keyb.nextLine();
} while (!possibleAge.matches("\\d+"))