使用hasNextInt和do-while循环，对于负整数没有错误消息

Question

I am writing a program that includes a test for whether the user input is a positive integer and displays an error messagge if the entry is a non-integer or negative. My code displays the intended error message if a non-integer is entered, but only re-prompts to enter a positive integer if a negative integer is entered. I've tried adding:

if (n <= 0);
System.out.print("You have not entered a positive integer"); 

before

 n = input.nextInt();

but that makes an error message appear even if a positive integer is entered.

I have also tried:

while (!input.hasNextInt() && n <= 0)

Any help is appreciated.

        Scanner input = new Scanner( System.in );
        int n = 0;

        do {
        System.out.print("Please enter a positive integer: ");
        while (!input.hasNextInt()){
            System.out.print("You have not entered a positive integer. \nPlease enter a positive integer: ");
            input.next();
        }
        n = input.nextInt();

        } while (n <= 0);

Answer 1

Try this:

int n = -1;//<-- it won't allow user to skip the loop after first pass without proper input
do {
    System.out.print("Please enter a positive integer: ");
    try {
        n = input.nextInt();//<-- in one pass ask input from user only once
        if(0 > n) {
            System.out.print("You have not entered a positive integer. \nPlease enter a positive integer: ");
        }
    } catch (NumberFormatException ex) {
        System.out.println("Invalid number !");
        break;//<-- break loop here, if don't wana prompt user for next input
    } catch(java.util.InputMismatchException ex) {
        System.out.println("Oops number is required !");
        break;//<-- break loop here, if don't wana prompt user for next input
    }
} while (n <= 0);

Answer 2

Try this:

int n = -1;
while (input.hasNextInt() && (n = input.nextInt()) < 0)
{
    // print error message about negative number
}

When the loop exits, if 'n' is still -1 you got to the end of the input, eg the user typed ctrl/d or ctrl/z depending on the platform.

If the user is at the console you might also need to skip to end of line.