要求提供整数作为输入，并退出是否q，但是如果其他字母再次尝试

Question

我正在处理一个程序，该程序将要求用户提供整数，然后询问另一个程序，然后将它们作为图表。然后，它将告诉他们他们之间的距离。用户必须输入整数或按" Q"退出。如果其他任何东西（不是整数或字母" Q"），它将告诉他们这是不正确的，请重试。我认为这就是我可以完成的方法，但它返回错误 cannot find symbol。非常感谢帮助！

import java.util.Scanner;
public class PointCheck{
   public static void main(String[] args){
      try {
         System.out.println("Welcome");
         System.out.println("To quit at anytime please type "Q". Enter point:");
         char Q = 'Q';
         char q = 'q';
         Scanner scan = new Scanner (System.in);
          input = scan.next();
         while (input.hasNext()) {
            if (input.hasNextInt()) {
               System.out.println("Int input");
            }
            else if (input.equals("Q")) {
               System.out.println("Exiting");
            }
            /*else {
               System.out.println("You did not enter a valid value. Please enter a number or "Q" to quit.");
            }*/
         }
      }
      catch(Exception e){
         System.out.println("Exiting Program.");
      }
   }
}

如果我不评论最后的其他语句，它只是默认为此，然后永远循环我的错误消息。

Answer 1

我已经对您的代码进行了一些修改，希望它有帮助：）

public class PointCheck {
/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    try {
        System.out.println("Welcome");
        System.out.println("To quit at anytime please type "Q". Enter point:");
        Scanner scan = new Scanner(System.in);
        while (scan.hasNext()) {
            if (scan.hasNextInt()) {
                System.out.println("Int input" + scan.nextInt());
            } else {
                String input = scan.next();
                if (input.equalsIgnoreCase("Q")){
                    System.out.println("Exiting");
                    break;
                }else {
                    System.out.println("You did not enter a valid value. Please enter a number or "Q" to quit.");
                }
            }
        }
    } catch (Exception e) {
        System.out.println("Exiting Program.");
    }
}
}

Answer 2

您可以尝试一下...输入只会仅用于整数，如果您输入除了Integer以外的任何内容，它将引发异常并移至catch块，该程序将终止程序。

import java.util.Scanner;
public class demo {
    public static void main(String[] args) {
        System.out.println("Welcome");
        System.out.println("Press any key to exit.. Enter point:");
        Scanner scanner= new Scanner(System.in);
        while (true){
            try {
                int number = scanner.nextInt();
                System.out.println(number);
            }
            catch (Exception e){
                System.exit(0);
            }
        }
    }
}

Answer 3

类似的东西可能是您喜欢的。在代码中阅读评论：

System.out.println("Welcome");
Scanner scanner= new Scanner(System.in);
int number = 0;
while (true){
    System.out.println("Enter point (q to quit): ");
    String strg = scanner.nextLine();
    // Get out of loop if q or Q or quit, 
    // or QUIT, or Quit, etc is entered.
    // providing the input actually contains
    // something.
    if (!strg.equals("") && strg.toLowerCase().charAt(0) == 'q') {
        break;
    }
    // Use the String.matches() method with regex to 
    // determine if an integer number was supplied.
    if (!strg.matches("\d+")) {
        System.err.println("Invalid Entry - Integer values only! Try again.n");
        continue;   // Start loop from beginning.
    }
    // Convert string number to Integer.
    number = Integer.parseInt(strg);
    break;  // Get outta loop      
}
String msg = "The number entered is: " + number;
if (number == 0) { msg = "Nothing Entered!"; }
System.out.println(msg);