try...catch block

[javaplus]

Hi,

I am trying to explore try catch block. I know a bit about it, but I am confused a little. How can I use multiple catch blocks with a try. And whats the use of finally in try catch block?

I normally use try catch in following way:

Code:

try{
...
}
catch(Exception ex)
{
ex.printStackTrace();
}

It serves the purpose for me but I have seen codes where developers mention a specific exception in the catch block. When to use that?

Regards.

[hardwired]

The more specific you can be the more information you can get about the trouble and thus the better equipped you can be to recover from it. Exceptions can be caught from more specific to more general. Using finally is a way to cleanup if an exception causes you to leave the execution of your code, eg, an error in reading a file causes execution to leave your try block and ends up in a catch block skipping over the br.close() statement. You could close the reader in a finally block. In pseudocode:

Code:

try {
    URL url = new URL(some_path);
    File file = new File(url.toURI());
    BufferedReader br = new BufferedReader(
                        new InputStreamReader(
                        new FileInputStream(file)));
    // read and process file
    br.close();
} catch(MalformedURLException mue) {
    System.out.println("Bad URL: " + mue.getMessage());
} catch(FileNotFoundException fnfe) {
    System.out.println("FileNotFound: " + fnfe.getMessage());
} catch(IOException ioe) {
    System.out.println("Read error: " + ioe.getMessage());
}

[javaplus]

Thanks. So the example you gave, can have br.close() in finally block.

Code:

try {
    URL url = new URL(some_path);
    File file = new File(url.toURI());
    BufferedReader br = new BufferedReader(
                        new InputStreamReader(
                        new FileInputStream(file)));
    // read and process file
} catch(MalformedURLException mue) {
    System.out.println("Bad URL: " + mue.getMessage());
} catch(FileNotFoundException fnfe) {
    System.out.println("FileNotFound: " + fnfe.getMessage());
} catch(IOException ioe) {
    System.out.println("Read error: " + ioe.getMessage());
}
finally{
br.close();
}

And what I know is, the finally block will execute even if no exception is caught. Is this right?

[hardwired]

the finally block will execute even if no exception is caught. Is this right?
Yes.
Closing the reader in the finally block may require another try-catch block for IOException.