Re: NullPointerException, IllegalArgumentException, or AssertionError for null constructor argument

Daniel Pitts wrote:


Here's an example of the difference between assertion and exception
generation. The assertion is forced to hold by the exception handling. If
the exception-handling algorithm were wrong, the null could perhaps slip
through, and the assert would fail. This should never happen.

The assert is there to alert us if the exception failed to do its job. The
programmer is asserting that the exception clause is sufficient.

public class NoNullHolder <T>
{
  private final T held;

  public NoNullHolder( T toHold )
  {
    if ( toHold == null )
    {
      throw new IllegalArgumentException( new NullPointerException(
         "null toHold" ));
    }
    held = toHold;
    assert held != null; // postcondition invariant
  }

  public final T getHeld()
  {
    assert held != null; // precondition invariant
    return held;
  }
}

--
Lew