java - 不允许使用文件未找到异常，但这是必要的

Question

所以我遇到了一个奇怪的问题，我试图使用 try-catch，但异常(exception)情况不允许。我会尽量清楚地描述这个问题。

一些背景:好的，所以任务基本上是允许用户写入一些文件并读取它们。因此，我在代码中调用以前创建的文件的部分。用户可以输入他们想要调用的文件，因此当然这个异常(exception)是强制性的。但错误表明永远不会抛出异常，但是当我运行代码时，它确实会被抛出。让我向您展示一些代码。

`while(error){
                    try{
                        response = scan.nextLine();


                        error = false;
                    }catch(FileNotFoundException e){
                        System.out.println("\nERROR:   ");
                        error = true;
                    }
                }`

好的，这是我编写的代码。现在这是我的输出(没有 try-catch 运行)

This is my output without using a try-catch

这是我的错误:

Exception in thread "main" java.lang.Error: Unresolved compilation problem: Unreachable catch block for FileNotFoundException. This exception is never thrown from the try statement body

at fileLab2.MemoMaker.main(MemoMaker.java:126)

希望有人能帮忙解决这个问题。我专门为了这个问题注册了这个账号，说实话，这很烦人。请询问您是否需要任何说明。

这是我的整个程序:

/*
 * tslaurenx
 * File reader lab 2
 * OOP
 * 11/20/15
 * Lab 8b
 * 
 */

package fileLab2;
import java.util.*
import java.io.*;

public class MemoMaker {

    public static void main(String[] args) throws IOException {


        int choice = 0;
        String name = "", response = "", memo = "";
        boolean running = true, error = true;

        String record = "";


        System.out.print("Hello, and welcome to the Memo Maker 2015. ");

        File memoTitles = new File("Memo Titles.txt");


        PrintWriter writeTitles = new PrintWriter(memoTitles);


        Scanner scan = new Scanner(System.in);


        while(running){

            while(error){
            System.out.println("\nPlease select an option.");
            System.out.println("\n(1) Create a Memo\n(2) View an Old Memo\n(3) Directions for Overwriting\n(4) Exit");



                try{
                    choice = scan.nextInt(); 

                    if(choice >4 || choice <1){
                        System.out.println("\nERROR: Do you see that number there? Okay then... try again.\n");
                        error = true;
                    }//close if
                    else error = false;

                }catch(InputMismatchException e){
                    scan.nextLine();
                    System.out.println("\nERROR: You need to enter the NUMBER next to your option.\n");
                    error = true;
                } //close catch

            }//close try while

            error = true;

            switch(choice){

            case 1:
                //create a file


                Scanner key = new Scanner(System.in);

                System.out.println("Enter the name of your memo.");
                name = key.nextLine();

                File file = new File(name + ".txt");


                record = record + "\n" +file.getName();


                writeTitles.print(record);

                writeTitles.close();


                PrintWriter write = new PrintWriter(file);

                System.out.println("\nOkay, now write your memo: ");

                memo = key.nextLine();

                write.println(memo);

                write.close();

                System.out.println("\nYour memo has been created.");

                break;


            case 2:
                //view an old file
                Scanner readTitles = new Scanner(memoTitles);
                Scanner enter = new Scanner(System.in);


                if(readTitles.hasNext() == false){
                    System.out.println("There are no files available. Begin with making a memo.");
                    running = true;
                    break;
                }//close if
                else{
                    //view a file

                    System.out.println("Here are your available memos. \nEXACTLY type the name of the memo that you wish to view.\n\n");

                    System.out.println(record);

                    while(error){
                        try{
                            response = enter.nextLine();

                            error = false;
                        }catch(FileNotFoundException e){
                            System.out.println("\nERROR:   ");
                            error = true;
                        }
                    }

                    error = true;

                    File trying = new File(response);

                    Scanner readMemo = new Scanner(trying);


                    System.out.println("\nHere is the message: ");

                    while(readMemo.hasNext() ){
                        String words = readMemo.nextLine();
                        System.out.println(words);
                    }//close while


                    while(error){
                        System.out.println("\n\nType 1 when you are finished viewing.");

                        int n = 0;

                        n = scan.nextInt();

                        if(n==1){
                            error = false;
                        }
                        else error = true;
                    }


                    readMemo.close();


                }//close else
                break;
            case 3:

                System.out.println("\nGo to Create a Memo, and type in the name of the file you wish to overwrite.\n");
                break;
            case 4:
                Scanner ans = new Scanner(System.in);

                int a = 0;

                System.out.println("Are you sure you wish to exit? All of your memos will be lost.");

                System.out.println("1. Yes\n2. No");

                while (error){

                    try{
                        a = ans.nextInt();

                        if(a != 1 && a !=2){
                            System.out.println("\nERROR: Please enter a valid option.");
                            error = true;
                        }//close if
                        else error = false;
                    }catch(InputMismatchException e){
                        System.out.println("\nERROR: Please enter a valid option.");
                        error = true;
                    }//close catch

                } //close try while

                error = true;

                if (a == 1){

                    System.out.println("Until next time!");
                    running = false;

                }// close if
                else {
                    running = true;
                }

            }//close switch




        }//close running

        scan.close();


        writeTitles.close();


    }//close main

}//close class

Answer 1

这一行，

File trying = new File(response);

即使，就像您在JavaDoc中看到的那样，也不会抛出任何异常，最好(但这不是强制性的)包含在您的try...catch<中 并使用 FileInputStream (它应该包含在 try block 内)因为它是 new FileInputStream() 构造函数抛出异常。在尝试高效读取文件时也不要使用 Scanner。

这是一个有用的链接:

• Best way to read a text file in Java

<小时/>

Javadoc

public File(String pathname) Creates a new File instance by converting the given pathname string into an abstract pathname. If the given string is the empty string, then the result is the empty abstract pathname.

这意味着它不会检查文件是否存在。

<小时/>

解决方案

FileInputStream fis = null;
try{
    fis = new FileInputStream(new File(enter.nextLine()));
    error = false;
} catch (FileNotFoundException e){
    // Blabla
}