使用Scanner.nextLine（）方法的时机

Question

From P.40 of the textbook 'Data Structures and Algorithms in Java, 6/e' (the code is slightly revised):

Scanner scanner = new Scanner(System.in);
System.out.print("Please enter an integer: ");
while (!scanner.hasNextInt()) {
    scanner.nextLine();
    System.out.print("Invalid int; pls enter an int: ");
}
int i = scanner.nextInt();
System.out.print(i);

If I type a non-integer value(that's to say: 1.0) by System.in, it would enter the while loop body since the boolean of !scanner.hasNextInt() is true.

However I don't understand the syntax the author puts in another line of scanner.nextLine(); inside the while loop in Line 4, does it generate anything? Why can't the program work if I delete the scanner.nextLine(); line? (and somehow pc memory almost get full after deleting it..)

Answer 1

What @Guy said is correct. The hasNext function call does not do anything to advance your input pointer. hasNextInt checks if your next input is an integer, but to advance to the next line after this input, you need to call a next function. Otherwise, you will forever be checking hasNextInt on your non-integer input, going into an infinite loop, which is why your memory usage is super high.