try without catch

[Manish Singhal]

import java.io.*;
class MyCatch{
    public static void main(String args[]) {
try{
   File f= new File("manish.txt");
   FileInputStream f1 = new FileInputStream(f);
  }
  //catch(IOException e ){}
finally{
  System.out.println("finally");
}
    }
  }

I am getting the below error while compiling the code, please explain:

MyCatch.java:9: unreported exception java.io.FileNotFoundException; must be caught or declared to be thrown
FileInputStream f1 = new FileInputStream(f);

[Rachel Swailes]

Originally posted by Manish Singhal:

 
try{
   File f= new File("manish.txt");
   FileInputStream f1 = new FileInputStream(f);
  }
  //catch(IOException e ){}
finally{
  System.out.println("finally");
}
    }
  }

I am getting the below error while compiling the code, please explain:

MyCatch.java:9: unreported exception java.io.FileNotFoundException; must be caught or declared to be thrown
FileInputStream f1 = new FileInputStream(f);

The line of code
FileInputStream f1 = new FileInputStream(f);
When you read in the API you will see that this throws an exception. If it throws an exception, the line of code must be placed in a try catch block that catches all of the exceptions.

You can also catch the biggest exception and deal with that one.

Example, for your code you could use either of the following three pieces of code...

try{
FileInputStream f1 = new FileInputStream(f);
}catch(FileNotFoundException fnfe){}
catch(IOException ioe){}


or

try{
FileInputStream f1 = new FileInputStream(f);
}catch(IOException ioe){}


or

try{
FileInputStream f1 = new FileInputStream(f);
}catch(Exception e){}

The first one is preferable

Cheers,
Rachel

[Manish Singhal]

Rachel, I agree with what you say but here would like to mention:

Question: Is the following code legal?
try {
...
} finally {
...
}
Answer: Yes, it's legal. A try statement does not have to have a catch statement if it has a finally statement. If the code in the try statement has multiple exit points and no associated catch clauses, the code in the finally statement is executed no matter how the try block is exited.

Any comments !!!
[ May 26, 2004: Message edited by: Manish Singhal ]

[Rachel Swailes]

Surely if you have code in the try bloc that is going to cause an exception to be thrown that you need a catch block to catch the exception? Maybe not to compile it but you need it from a logic point.

Even when you compiled it, it said that you were not catching the exception. And if you write code that does not throw an exception then why do you want to do it in a try finally block?

[Carl Trusiak]

A try - finally block is used usually in a method that declares to throw any Checked Exceptions that can occur. in your example, if you changed the declaration of main to be:
public static void main(String args[]) throws IOException
The code will compile just fine.

Typically, you use try - finally when you want to ensure some cleanup is done, even if an Exception is thrown but, do not wish to handle the Exception thrown in any way.A fair example would be SQL code

   public User login(String userName, String password) throws SQLException{
        Connection conn = DriverManager.getConnection(....);
        try{
           ...
           //execute SQL, get results etc.
           return user;
        }
        finally{
            try{
               conn.close();
            }
            catch(SQLException sqle){
                //nothing to worry about on sqlexception on connection.close
                //just ignore it
            }
         }
     }

[Rachel Swailes]

Well, the way that I code at the moment is to deal with java's exceptions when they occur. Could you give me an example of when to keep throwing the exceptions would be better?

[Manish Singhal]

Carl, thanks for the clear explanation.

[Jose Botella]

Rachel, sometimes the information necessary to deal with the exception is not present in the object containing the method in which the exception was thrown. The exception can progress untill is caught by a method in an object that knows how to recover. Doing so you can centralize the exception handling code for a family of exceptions.