CODEWITHSUNDEEP
javaexception
ankush981
ankush981

Reputation: 5417

Compiler error despite catching IOException

The following program for file I/O is taken from the standard Oracle docs:

//Copy xanadu.txt byte by byte into another file
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class CopyBytes
{
    public static void main(String[] args) //throws IOException
    {
        FileInputStream in = null;
        FileOutputStream out = null;

        try
        {
            in = new FileInputStream("xanadu.txt");
            out = new FileOutputStream("xanadu_copy.txt");
            int c;

            while((c = in.read()) != -1)
            {
                out.write(c);
            }
        } 
        catch (IOException e)
        {
            System.out.println("IO exception : " + e.getMessage());
        }
        finally
        {
            if (in != null)
            {
                in.close();
            }
            if (out != null)
            {
                out.close();
            }
        }
    }
}

As you can see, I commented out the throws IOException part, thinking that since I'm catching it in the code, all should be fine. But I'm getting a compiler error:

CopyBytes.java:32: error: unreported exception IOException; must be caught or declared to be thrown
                in.close();
                        ^
CopyBytes.java:36: error: unreported exception IOException; must be caught or declared to be thrown
                out.close();
                         ^
2 errors

The errors vanish when I include the throws IOException part, but I'm confused. Isn't it enough that I'm catching the exceptions?

Upvotes: 2

Views: 415

Answers (3)

Sachin Gupta
Sachin Gupta

Reputation: 8358

In your finally block you are using in.close() statement to close the stream. This statement also throws IOException. You can avoid this exception by adding try/catch block to these close statements.

Upvotes: 4

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726539

In order to not have to report an exception you need to put it in the try portion of the try/catch/finally block. Exceptions thrown in the catch and finally parts are not caught, prompting the compiler error:

try {
    ... // Exceptions thrown from here will be caught
} catch (ExceptionOne e1) {
    .. // Exceptions thrown from here need to be declared
} catch (ExceptionTwo e2) {
    .. // Exceptions thrown from here need to be declared
} finally {
    .. // Exceptions thrown from here need to be declared
}

Upvotes: 3

Eran
Eran

Reputation: 393801

You are not catching the potential IOException that might be thrown in your finally block.

You can fix it by adding try-catch to the finally block:

    finally
    {
      try {
        if (in != null)
        {
            in.close();
        }
        if (out != null)
        {
            out.close();
        }
      }
      catch (IOException ex) {
      }
    }

Upvotes: 6

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