java - 无法让我的 MismatchException 与 switch 一起正常工作

Question

问题已解决。

所以我正在完成我的作业，最后要做的就是实现一些简单的错误处理，但事实证明我不太确定我做错了什么。

我有 5 个案例，需要输入 0、1、2、3、4。效果很好。

但是如果输入不是数字，它应该显示一条消息，并让用户输入一些新的输入。每项任务完成后，您应该会看到菜单并能够制作新的coice。

我可以打印消息，但无法接受新的输入。我理解这个问题以及为什么会发生，但我不知道如何实际解决它。

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.InputMismatchException;
import java.util.Scanner;

public class ObscureLovecraft {

    public static void main(String[] args) {
        // Looking for files and opening scanner
        File file = new File("./lovecraft.txt");
        File readObscure = new File("./obscure.txt");
        Scanner sc = new Scanner(System.in);

        // Printing UI

        printMenu();

        // Taking input, looping until case 0 is executed
        // Printing menu after each iteration
        // Switch, prints a new menu after every iteration
        try {
        int input = sc.nextInt();

            while (input != 0) {

                switch (input) {
                case 1:
                    writeObscure(file);
                    printMenu();
                    input = sc.nextInt();
                    break;

                case 2:
                    translateObscure(readObscure);
                    printMenu();
                    input = sc.nextInt();
                    break;

                case 3:
                    printObscure();
                    printMenu();
                    input = sc.nextInt();
                    break;

                case 4:
                    printTranslated();
                    printMenu();
                    input = sc.nextInt();
                    break;

                case 0:
                    kill();
                    break;

                }
            }
        } catch (InputMismatchException e) {
            System.out.println("You must use numbers.");
            sc.nextInt();
        }

        sc.close();

        System.out.println(":(");

    }

    public static void switches() {

    }

    /**
     * Just a method printing our menu
     */
    public static void printMenu() {
        System.out.println();
        System.out.println("Obscure");
        System.out.println("=======");
        System.out.println("1. Make obscure");
        System.out.println("2. Make readable");
        System.out.println("3. Print obscure");
        System.out.println("4. Print readable");
        System.out.println("0. Exit");
    }

    /**
     * Method which will print the "obscured" version of the text
     * 
     * @param file path to the file
     */
    public static void writeObscure(File file) {
        // Create new output file, creating PrintWriter, StringBuilder and placeholder
        // for the text
        File outFile = new File("./obscure.txt");
        StringBuilder buf = new StringBuilder();
        try {
            PrintWriter pw = new PrintWriter(outFile);
            Scanner fileSc = new Scanner(file);
            String text = "";

            // Placeholder for chars, looping through the file, adding it to placeholder
            // text, with new line
            char c;
            while (fileSc.hasNextLine()) {
                text = (fileSc.nextLine() + "\n");
                // Looping through the text, taking each character, pushing it 3 steps in the
                // alphabet
                // Taking care of z/Z pushing it to a/A, should maybe be c/C? Oh well.
                // Appending it to the stringbuilder in the new order
                // Casting char to int, to get ascii value
                for (int i = 0; i < text.length(); i++) {
                    c = text.charAt(i);
                    if (c == 'z') {
                        buf.append('a');
                    } else if (c == 'Z') {
                        buf.append('A');
                    } else {
                        int ascii = (int) c;
                        char nextChar = (char) (ascii + 3);
                        buf.append(nextChar);
                    }

                }
            }
            fileSc.close();

            // Printing and closing
            pw.print(buf);
            pw.close();
            System.out.println("Done");
        } catch (FileNotFoundException e) {
            System.out.println("Seems like a file gone missing, check error message: " + e.getMessage());
            System.out.println("Printing stacktrace: ");
            e.printStackTrace();
        }
    }

    /**
     * Method which will translate the obscured text to normal, Basically same as
     * the method above, but in reversed order
     * 
     * @param file
     */
    public static void translateObscure(File file) {
        // Read the file:
        StringBuilder obsBuf = new StringBuilder();
        try {
            Scanner readSC = new Scanner(file);
            // Print the file
            File printReadable = new File("./readableLovecraft.txt");
            PrintWriter pwRead = new PrintWriter(printReadable);

            // Text
            String readableText = "";
            char readC;

            // Loop thru
            // Something weird happend with empty lines,
            // Had to manually skip them
            while (readSC.hasNextLine()) {
                readableText = (readSC.nextLine() + "\n");

                for (int i = 0; i < readableText.length(); i++) {
                    readC = readableText.charAt(i);
                    if (readC == '\n') {
                        obsBuf.append(readC);
                    } else if (readC == 'z') {
                        obsBuf.append('a');
                    } else if (readC == 'Z') {
                        obsBuf.append('z');
                    } else {
                        int ascii = (int) readC;
                        char nextChar = (char) (ascii - 3);
                        obsBuf.append(nextChar);
                    }
                }

            }
            readSC.close();

            // Printing and closing
            pwRead.print(obsBuf);
            pwRead.close();
            System.out.println("Done");
        } catch (FileNotFoundException e) {
            System.out.println("Seems like a file gone missing, check error message: " + e.getMessage());
            System.out.println("Printing stacktrace: ");
            e.printStackTrace();
        }
    }

    /**
     * Simple method which loops through the text and prints it
     */
    public static void printObscure() {
        File readOutFile = new File("./obscure.txt");
        try {

            Scanner fileSc = new Scanner(readOutFile);
            String readText = "";
            while (fileSc.hasNextLine()) {
                readText = (fileSc.nextLine());
                System.out.println(readText);
            }
            fileSc.close();
        } catch (FileNotFoundException e) {
            System.out.println("Seems like a file gone missing, check error message: " + e.getMessage());
            System.out.println("Printing stacktrace: ");
            e.printStackTrace();

        }
    }

    /**
     * Simple method which loops through the text and prints it
     */
    public static void printTranslated() {
        File readReadOutFile = new File("./readableLovecraft.txt");
        String readReadText = "";
        Scanner fileSc;
        try {
            fileSc = new Scanner(readReadOutFile);

            while (fileSc.hasNextLine()) {
                readReadText = (fileSc.nextLine() + "\n");
                System.out.println(readReadText);

            }
            fileSc.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            System.out.println("Seems like a file gone missing, check error message: " + e.getMessage());
            System.out.println("Printing stacktrace: ");
            e.printStackTrace();
        }
    }

    /**
     * Method which kills the program
     */
    public static void kill() {
        System.exit(1);
    }
}

Answer 1

1- Create a new method and put your logic into it

2- Delete while from your code

3- Throws InputMismatchException in default block

4- Call the newMethod() in cases instead of input = sc.nextInt. (recursive)

5- Call the newMethod() in catch block (recursive)

public static void newMethod() {
        
        Scanner sc = new Scanner(System.in);

        try {

            int input = sc.nextInt();

            switch (input) {
                case 1:
                    writeObscure(file);
                    printMenu();
                    newMethod();
                    break;

                case 2:
                    translateObscure(readObscure);
                    printMenu();
                    newMethod();
                    break;

                case 3:
                    printObscure();
                    printMenu();
                    newMethod();
                    break;

                case 4:
                    printTranslated();
                    printMenu();
                    newMethod();
                    break;

                case 0:
                    kill();
                    break;

                default:
                    throw new InputMismatchException();
            }

        } catch (InputMismatchException e) {
            System.out.println("You must use numbers.");
            newMethod();
        }

      sc.close();

}

Change your main method like this

 public static void main(String[] args) {

            File file = new File("./lovecraft.txt");
            File readObscure = new File("./obscure.txt");
            printMenu();
            
            //Call new Method
            newMethod();
            
    }