[Colloq] PhD Thesis Defense - Richard Cobbe

[Rachel Kalweit]

Richard Cobbe will give his Thesis Defense on December 1, 2008 at 1:30pm in room 366 WVH.

Title: Putting Java's Null in its Place: Much Ado About Nothing

Abstract:
  Mainstream object-oriented languages include a "null" value that
  inhabits every object type and that pervades programs.  It exists both
  because the language semantics requires it in certain places and because
  it is the most convenient representation for common patterns, such as a
  sentinel values to indicate failure.  Safety requires implementations of
  these languages to insert run-time checks throughout programs to
  determine whether object references are null at each field lookup and
  method call.

  The ubiquity of "null" in object-oriented programs leads to severe
  engineering problems for programmers.  First, the error messages issued
  by the run-time checks are typically not sufficiently informative to help
  the programmer find the source of the error.  Second, the type systems in
  OO languages generally do not distinguish "null" from other values of
  (object) type, preventing the programmer from stating important
  invariants about the flow of "null" in the type system.  Third,
  programmers' standard use of "null" as a sentinel does not
  unambiguously represent failures.  To resolve or avoid these ambiguities,
  component authors must incorporate additional complexity into their
  interfaces, and this complexity can lead to subtle bugs.

  In this dissertation, we propose two changes to Java that allow us to
  completely remove the "null" value.  Doing so addresses the problems
  above and provides significant engineering benefits to the programmer.
  Further, we demonstrate the practical feasibility of our proposal with a
  migration path that allows programmers to shift large codebases from Java
  to our new language, one class at a time.

Committee:
    Matthias Felleisen (advisor)
    Karl Lieberherr
    Olin Shivers
    Robert Muller, Boston College