This method prevents a common user error: input chars where have to input numbers.
Basically, it uses recursion and some other inner properties of the class Scanner, like the method nextline().
It Receives a input stream as argument.

public int readOnlyIntegers(Scanner in) 
    {

        int integer = 0;
            try
                {
                    integer = in.nextInt();
                }
                catch(Exception e)
                {
                    System.out.printf("only numbers are allowed");
                    in.nextLine();
                    integer = readOnlyIntegers(in);
                }
        return integer;
    }