[Colloq] Reminder: PhD Thesis Defense - Richard Cobbe - Today, 1:30
Rachel Kalweit
rachelb at ccs.neu.edu
Mon Dec 1 09:00:05 EST 2008
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
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