Scanner keeps skipping input whist using nextInt() and loops

问题

I am using a while loop to make sure that the value entered to a scanner object is an integer as such:

while (!capacityCheck) {
        try {
            System.out.println("Capacity");
            capacity = scan.nextInt();
            capacityCheck = true;
        } catch (InputMismatchException e) {
            System.out.println("Capacity must be an integer");
        }
    }

however, if the user does not enter an integer, when it should go back and take another input it just repeatedly prints "Capacity" followed by the output in the catch without asking for more input. How do I stop this?

回答1:

scan.nextLine();

Put this piece of code inside your catch block, to consume the non integer character along with the new line character which is stays in the buffer(hence, infinitely printing the catch sysout), in the case where you've given a wrong input.

Ofcourse, there are other cleaner ways to achieve what you want, but I guess that will require some refactoring in your code.

回答2:

Use the following:

while (!capacityCheck) {
        System.out.println("Capacity");
        String input = scan.nextLine();
        try {
            capacity = Integer.parseInt(input );
            capacityCheck = true;
        } catch (NumberFormatException e) {
            System.out.println("Capacity must be an integer");
        }
    }

回答3:

Try this :

while (!capacityCheck) {
    try {
        System.out.println("Capacity");
        capacity = scan.nextInt();
        capacityCheck = true;
    } catch (InputMismatchException e) {
        System.out.println("Capacity must be an integer");
        scan.nextLine();
    }
}

回答4:

Try putting this at the end of the loop -

scan.nextLine();

Or better to put it in the catch block.

    while (!capacityCheck) {
        try {
            System.out.println("Capacity");
            capacity = scan.nextInt();
            capacityCheck = true;
        } catch (InputMismatchException e) {
            System.out.println("Capacity must be an integer");
            scan.nextLine();
        }
    }

回答5:

I see no need for a try/catch or capacityCheck as we have access to the method hasNextInt() - which checks if the next token is an int. For instance this should do what you want:

    while (!scan.hasNextInt()) { //as long as the next is not a int - say you need to input an int and move forward to the next token.
        System.out.println("Capacity must be an integer");
        scan.next();
    }
    capacity = scan.nextInt(); //scan.hasNextInt() returned true in the while-clause so this will be valid.

来源：https://stackoverflow.com/questions/15516036/scanner-keeps-skipping-input-whist-using-nextint-and-loops