Question

In trying to refactor some I code I attempted to throw the exception in the catch clause like so –

try {
....
}
catch(Exception exception){
.....
throw exception
}

However when I attempted to throw the exception on line “throw exception” the compiler complained with a message that I needed to surround my throw clause in a new try/catch like so –

try
{
  ....
}
catch (Exception exception)
{
  .....
  try
  {
    throw exception
  }
  catch (Exception e2)
  {
     ...
  }
}

Why does the compiler require this and what use does it provide ?

Thanks

Answer 1

My guess is that your trying to throw an exception sub class that isn’t declared by the method as an exception type it can throw.

The following example works

package test.example;

public class ExceptionTest {

    public static void main(String[] args) throws Exception{
        try {
            int value = 1/0;
        } catch (Exception e) {
            System.out.println("woops the world is going to end");
            throw e;
        }

    }

}

However this example will give an error.

package test.example;

public class ExceptionTest {

    public static void main(String[] args) throws RuntimeException{
        try {
            int value = 1/0;
        } catch (Exception e) {
            System.out.println("woops the world is going to end");
            throw e;
        }

    }

}

Note in the second example I’m simply catching Exception not RuntimeException, it won’t compile as I throw Exception which is an undeclared throws, even though I do declare RuntimeException.

Yes the exception is a RuntimeException but the compiler doesn’t know that.

Just thought of a third working example to show you. This one also works because your throwing the same type as you declare. (note the only change is the catch block)

package test.example;

public class ExceptionTest {

    public static void main(String[] args) throws RuntimeException{
        try {
            int value = 1/0;
        } catch (RuntimeException e) {
            System.out.println("woops the world is going to end");
            throw e;
        }

    }

}

You need to understand the differences between all three of these answers