Java中实现输入验证失败后回到输入语句重新执行的方案（含异常处理场景）

Got it, let's refactor your code to keep asking for input until the user provides a valid number that corresponds to an existing .ics file. The key here is wrapping your input/validation logic in a loop, and handling both the input mismatch and missing file cases without exiting.

Here's the revised code: #

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.InputMismatchException;
import java.util.Scanner;

public class FileInputHandler {
    public static void main(String[] args) {
        short x = 0;
        Scanner scan = new Scanner(System.in);
        boolean validInput = false;

        // Loop until we get valid input + existing file
        while (!validInput) {
            try {
                System.out.print("Please enter a number: ");
                x = scan.nextShort();
                Path path = Paths.get(x + ".ics");

                if (!Files.exists(path)) {
                    System.out.println("Sorry, file does not exist. Please try again.");
                    continue; // Skip to next iteration of the loop
                }

                // If we reach here, input is valid and file exists
                validInput = true;
            } catch (InputMismatchException e) {
                System.out.println("Sorry, please enter a valid number.");
                scan.nextLine(); // Clear the invalid input from the scanner buffer
            }
        }

        // Now execute the code that comes after valid input
        File f = new File(x + ".ics");
        try (Scanner classScan = new Scanner(f)) {
            byte i = 1;
            for (; i <= 6; i++) {
                if (classScan.findWithinHorizon(String.valueOf(i), 0) != null) {
                    break;
                }
            }
            System.out.println("Found match at: " + i);
        } catch (IOException e) {
            // Handle potential file read errors (good practice!)
            System.out.println("Error reading the file: " + e.getMessage());
        }

        scan.close();
    }
}

Key changes explained: #

• Loop with a validation flag: We use boolean validInput to track when we have a valid input + existing file. The loop runs until this flag is true.
• Handling missing files: Instead of exiting, we use continue to jump back to the start of the loop and ask for input again.
• Clearing invalid input: When InputMismatchException is thrown, the invalid input (like a string) stays in the scanner's buffer. Calling scan.nextLine() clears it, so the next scan.nextShort() doesn't immediately throw the same exception again (this prevents an infinite loop!).
• Proper resource cleanup: Added scan.close() to clean up the scanner, and added a catch for IOException when reading the file (since Scanner(File) can throw it, which your original code didn't handle).
• User prompts: Added a prompt asking the user to enter a number, which makes the program more user-friendly.

This approach keeps the program running until the user provides valid input, then proceeds to process the file as intended.

内容的提问来源于stack exchange，提问作者gooooodmorning