Geek asks and answers

Why is it necessary to be able to throw an exception in an attempt to write a catch?

I played with some programs with exceptions and came across with the fact that I was surprised that I had never met before.

import java.io.*;

class ExceptionTest
{
  public static void main(String[] args)
  {
    try
    {
      System.out.println("hello");
    }
    catch(IOException ioe)
    {
      System.err.println("ioexception was thrown!!");
    }
  }
}

a compiler error occurs:

ExceptionTest.java:10: exception java.io.IOException is never thrown in body of
corresponding try statement
catch(IOException ioe)
^
1 error

My question is: why is this so?

Why is the compiler worried about a piece of code, it is sure that it will never reach. It may just be a warning, not a complete mistake. In the end, we might want to keep the catch block as a backup for some future changes that we could make, or maybe the programmer just forgot to delete it after some changes.

I know that I know that this saves us from unnecessary keystrokes, etc. But this should not interfere with the compiler to cause an error. Or is there some other reason for this?

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