How to display my own FileNotFoundException message

Question

I'm having a problem with custom exception throwing in Java. Specifically, I'd like to intentionally throw a FileNotFoundException in order to test a method called fileExists(). The method tests if the file (A) doesn't exist, (b) is not a normal file, or (c) is not readable. It prints a different message for each situation. However, when running the following code, the main method displays the default FileNotFoundException message, rather than one in the fileExists method. I'd love to hear any thoughts as to why. All variables were declared, but I did not include all of the declarations here.

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

        inputFile = new File(INPUT_FILE);  // this file does not exist
        input = new Scanner(inputFile);
        exists = fileExists(inputFile);
        System.out.println("The file " + INPUT_FILE 
                + " exists. Testing continues below.");

    } catch (FileNotFoundException ex) {
        System.err.println(ex.getMessage());
    }

}

public static boolean fileExists(File file) throws FileNotFoundException {
    boolean exists = false;    // return value
    String fileName = file.getName();  // for displaying file name as a String

    if ( !(file.exists())) {
        exists = false;
        throw new FileNotFoundException("The file " + fileName + " does not exist.");
    }

    else if ( !(file.isFile())) {
        exists = false;
        throw new FileNotFoundException("The file " + fileName + " is not a normal file.");
    }

    else if ( !(file.canRead())) {
        exists = false;
        throw new FileNotFoundException("The file " + fileName + " is not readable.");
    }

    else {
        exists = true;
    }

        return exists;

}

Call `fileExists(inputFile)` *before* `new Scanner(inputFile)`. If you checked the stacktrace, you'd see that your code is failing in `new Scanner(inputFile)`, and hence never gets to your code. — Andreas, Feb 19 '19 at 22:36

score 0 · Accepted Answer · answered Feb 19 '19 at 22:58

First of all you might want to avoid using same class names as existing Java classes so as to avoid the confusion.

In your main method, you would want to check if the file exists before you use create the Scanner object.

Also, there is no need for all the exists = false where you will be throwing an exception as the code stops there.

A possible solution will be as follows:

public static boolean fileExists(File file) throws FileNotFoundException {
    String fileName = file.getName();  // for displaying file name as a String

    if (!(file.exists())) {
        throw new FileNotFoundException("The file " + fileName + " does not exist.");
    }

    if (!(file.isFile())) {
        throw new FileNotFoundException("The file " + fileName + " is not a normal file.");
    }

    if (!(file.canRead())) {
        throw new FileNotFoundException("The file " + fileName + " is not readable.");
    }

    return true;
}

public static void main(String[] args) throws Exception {
    String INPUT_FILE = "file.txt";

    try {
        File inputFile = new File(INPUT_FILE);

        if (fileExists(inputFile)) {
            Scanner input = new Scanner(inputFile);

            System.out.println("The file " + INPUT_FILE + " exists. Testing continues below.");
        }
    } catch (FileNotFoundException ex) {
        System.err.println(ex.getMessage());
    }
}

Thanks. What exactly do you mean by using the names of existing java classes? Are you just referring to the FileNotFoundException class? — Jacob Torres, Feb 21 '19 at 18:21
@Jake Yes, as you mentioned, Java has it's own FileNotFoundException in which if you forget to import yours you would end up with the other. — Omari Celestine, Feb 21 '19 at 18:23

score 0 · Answer 2 · answered Feb 19 '19 at 22:59

0

You could also alternatively create a class in which extends FileNotFoundException give it a File as a param and then throw that in your catch instead and proceed to override your printouts in that said class.

answered Feb 19 '19 at 22:59

Cody Hafemeister

72
6

How to display my own FileNotFoundException message

2 Answers2