执行while循环和用户输入问题

Question

我正在尝试制作一个用户需要输入随机整数的程序。如果用户输入字符串，我希望弹出错误消息：“这不是数字”，然后重启程序，直到用户输入数字为止。到目前为止我已经知道了，但是我被卡住了。如果我输入一个字符串并且程序崩溃，我只会收到一条错误消息。

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int number = 0;


    do {
        System.out.println("Input a number!");
        number = scanner.nextInt();
        if (!scanner.hasNextInt()) {
            System.err.println("This is not a number");
        }

    } while (!scanner.hasNextInt());

    System.out.println("You entered: " + number);

}

Answer 1

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    String input = "";
    int number = 0;
    boolean end = true;


    do {
        System.out.println("Input a number!");
        input = scanner.nextLine();
        try {
            number = Integer.parseInt(input);
            end = true;
        } catch(Exception e) {
            System.err.println("This is not a number");
            end = false;
        } 

    } while (!end);

    System.out.println("You entered: " + number);

}

Answer 2

public class Solution {

  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    String number;
    do {
        System.out.println("Input a number!");
        number = scanner.next();
    } while (!isNumeric(number));

    System.out.println("You entered: " + number);
  }

  public static boolean isNumeric(final String str) {
    // null or empty
    if (str == null || str.length() == 0) {
        return false;
    }
    return str.chars().allMatch(Character::isDigit);
  }
}

Answer 3

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int number = 0;
        boolean valid;
        do {
            valid = true;
            System.out.print("Input an integer: ");
            try {
                number = Integer.parseInt(scanner.nextLine());
            } catch (NumberFormatException e) {
                System.out.println("This is not an integer. Try again.");
                valid = false;
            }
        } while (!valid);

        System.out.println("You entered: " + number);
    }
}

示例运行：
Input an integer: a
This is not an integer. Try again.
Input an integer: 12.34
This is not an integer. Try again.
Input an integer: 45
You entered: 45

注意：

使用Scanner:nextLine代替Scanner::nextInt；特别是在循环处理输入时。检查Scanner is skipping nextLine() after using next() or nextFoo()?了解更多信息。

[scanner.hasNextInt()应在scanner.nextInt()之前使用，即

    if(scanner.hasNextInt()) {
        number = scanner.nextInt();
    }

如果要输入任何数字（不仅是整数），请使用number = Double.parseDouble(scanner.nextLine());，但请确保将number声明为double变量，即声明为double number = 0.0。