尽管终止表达式，循环也不会结束

Question

Hello Stack overflow community,

My prompt is: **" You will do error checking to make sure that the hour entered is in the range [0, 23]. Keep asking the user until the user enters a time within the valid range.

My program when it has the correct integer inputs (any int input really) will work correctly. However, if i enter a non-int, then everything is stuck in an infinite loop.

What am I doing wrong?

   import java.util.*;
public class Tester2 {
    int a; // any valid int number

public void loop() 
{
    Scanner sc = new Scanner(System.in);
    int x=0; // terminating int
    while(x==0) 
    {
        System.out.println("Enter 0-23: ");


            try
            {
                if(sc.hasNextInt()) 
                {
                    a=sc.nextInt();
                    if((a>=0&&a<=23)) 
                    {
                        System.out.println("Success! ");
                        x=1;
                    }
                    else 
                    {
                        System.out.println("Retry! ");
                        a=0;
                        x=0;
                    }
                }
            }
            catch (NumberFormatException ex) 
            {
                System.out.println("invalid input");
            }

        }

}

}

Answer 1

sc.hasNextInt() will return false if the next element to be read is not a valid integer. However, this element is not read at any point in your code in that case.

You should ensure that this element is read and discarded when sc.hasNextInt() is false (adding sc.next() inside an else block should do the trick).