使用我创建的Exception类捕获抛出的异常

Question

In GraphicsFileNotFoundException.java all I have is an import of FileNotFoundException and the class GraphicsFileNotFoundException which extends FileNotFoundException .

In my main java file, I'm trying to read in a graphics file with the method getGraphicsFile which throws GraphicsFileNotFoundException .

My brain is pooped after a good 40 minutes trying to find out how to catch this exception. I've tried using a try-catch block and catching GraphicsFileNotFoundException but I still get the error

unreported exception GraphicsFileNotFoundException ; must be caught
   or declared to be thrown.



public void getGraphicsFile(String fileName) throws GraphicsFileNotFoundException {
    String graphics = "";
    Scanner getGraphics = null;
    try { 
      getGraphics = new Scanner(new File(fileName));
    }

    catch (GraphicsFileNotFoundException e){
      System.out.println("Error! File can't be found :/");
    }

Answer 1

You need to either properly extend the FileNotFoundException class or manually throw an exception inside your try block.

Assuming this is for an assignment (I'm not sure why else you'd need to specifically extend this exception) you'll need to take another look at your GraphicsFileNotFoundException class and make sure that it does what it needs to.

To throw an exception, simply write your condition and the throw statement:

if(needToThrow) {
    throw new GraphicsFileNotFoundException();
}

To catch an exception, surround the throw statement with a try block immediately followed by a catch block.

try {
    // code here
    if(needToThrow) {
        throw new GraphicsFileNotFoundException();
    }
}
catch(GraphicsFileNotFoundException e) {
    // handle the error (print stack trace or error message for example)
    e.printStackTrace(); // this is printing the stack trace
}

I recommend using Eclipse if you aren't already because many times it will offer to surround throw statements that need to be caught with a automatically generated try catch block.