文件存在于与程序相同的文件夹中的FileNotFoundException

Question

Similar questions deal with files on the C: drive, where hardcoding the file path is an acceptable answer. This application is mobile, and hardcoding the file path is not practical.

I am trying to import a text file via scanner, that contains a list of strings, 15 characters each, 1 per line. LOTS of lines. The file name is a.txt .

I call it using

File data = new File("a.txt");
Scanner in = new Scanner(data);

repeated the lines below with "b.txt", using different Object names.

However, when I build the program, I get this error log (using Jcreator IDE):

--------------------Configuration: <Default>--------------------
E:\Simple Encryption\Simple_Encryption.java:17: unreported exception java.io.FileNotFoundException; must be caught or declared to be thrown
    Scanner in = new Scanner(data);
                 ^
E:\Simple Encryption\Simple_Encryption.java:18: unreported exception java.io.FileNotFoundException; must be caught or declared to be thrown
    Scanner numsIn = new Scanner(nums);
                     ^
2 errors

Process completed.

The program is in the folder E:/Simple Encryption/ , which contains the following files and folders:

• Simple_Encryption.java
• Simple_Encryption.class
• lock.png (unused)
• a.txt
• b.txt (same error as a.txt on import, just one line below)
• /images (folder, contains icon.png)

There is nothing else in the folder. I cannot hardcode the file path because on different computers, it has different drive names, and will be distributed under different folders later. (Here (School), it's on the E: drive, at home it's the J: drive, and at work it's on the G: drive.)

Although I have gotten help from existing errors, I need to import this on the program startup, and not just skip it. The file exists in it's current form, and the program cannot function without it.

What is causing this error? And what can I do to prevent this?

Answer 1

E:\Simple Encryption\Simple_Encryption.java:17: unreported exception 
java.io.FileNotFoundException; must be caught or declared to be thrown

As your exception saying you need to use try- catch block

try {
   Scanner numsIn = new Scanner(nums);
catch (FileNotFoundException e) {
  // do something
} finally {
  if (numsIn != null) numsIn .close();
}

OR

you need to throw that exception though calling method

public static void xxxx() throws FileNotFoundException {
   // do something
}

Answer 2

The problem is not the exception that is thrown, but the fact that the constuctor is declared as throwing the FileNotFoundException checked exception.

public Scanner(File source) throws FileNotFoundException

Since it is a checked exception it must be handled by the programmer, because it is used to signal something that may happen.

So you must enclose them in a try/catch statement:

Scanner in = null;
try {
  in = new Scanner(file);
}
catch (FileNotFoundException e) {
  e.printStackTrace();
}

Answer 3

As you say the file exists, but it states that it cannot find the file. Try this:

System.out.println(data.getAbsolutePath());

This should let you know exactly where it is looking for the file, and you can then tweak the app without using full paths