1. Group 4: Song Li, Ying Lu, Hexin Wang, and Michael Walker May 1, 2000
Java ParTy:
Java With Parameterized Types
“Tonight I’m gonna ParTy like it’s
1999.”
Prince
Background
just got here last week
finished degree at MIT week before
Philosophy of advising students
don’t come to grad school to implement someone else’s idea
can get paid more to do that in industry
learn to be a researcher
important part of that is deciding what problems and ideas are worth spending time on
grad students should have their own project
looking for students who can come up with their own ideas for research
will take good students interested in things I’m interested in – systems, programming languages & compilers, security
rest of talk – give you a flavor of the kinds of things I am interested in
meant to give you ideas (hopefully even inspiration!) but not meant to suggest what you should work on
CS655: Programming Languages
University of Virginia
Computer Science
Group 4: Song Li, Ying Lu,
Hexin Wang, and Michael Walker
May 1, 2000

2. University of Virginia CS 655
Outline
Motivation
Related Work
Our Solution: ParTy
Evaluation
Remaining Work
Conclusion
22 July 2019
University of Virginia CS 655

3. University of Virginia CS 655
Motivation
Java provides no support for genericity [JLS]
Must use Object parameters with type casting
Performance hit
Type safety is an issue
22 July 2019
University of Virginia CS 655

4. Genericity: Potential Benefits
Ideal scenario:
One generic abstraction that adapts
Compiled code is JVM-compatible
Type safety control is just as powerful as non-generic code
Performance boost in execution speed
Small code size
22 July 2019
University of Virginia CS 655

5. Genericity: Potential Benefits
ParTy scenario:
One generic abstraction that adapts
Compiled code is JVM-compatible
Type safety control is just as powerful as non-generic code
Performance boost in execution speed
Small code size
We can’t have everything! But we can delay code blowup...
22 July 2019
University of Virginia CS 655

6. University of Virginia CS 655
Related Work
Examine support for type parameters in other languages
C++, Ada, Sather, Eiffel, Haskell, ML
Examine current proposals for Java extensions
GJ, PolyJ, Pizza, Agesen et. al.
22 July 2019
University of Virginia CS 655

7. Related Work: GJ and Pizza [Bracha+98]
GJ translates into legal JVM bytecode
Homogeneous genericity
Substitutes type variables by their “bounding type”
usually, Object
Constrains code size
Sacrifices speed
No type constraints
22 July 2019
University of Virginia CS 655

8. Related Work: PolyJ [Liskov+97]
Modifies JVM bytecode to express parameterization
better performance
small code size
Adds where clause type constraints a la CLU [LSA+77]
Creates a new language
22 July 2019
University of Virginia CS 655

9. Related Work: Agesen et. al. (Stanford, 1997)
Insert preprocess step into JVM loader
no change to JVM
delays code blowup until load-time!
No type constraints
Details of implementation are vague
22 July 2019
University of Virginia CS 655

10. Related Work: Comparison
22 July 2019
University of Virginia CS 655

11. University of Virginia CS 655
Java ParTy Philosophy
Provide a powerful, safe, and efficient construct for designing generic classes without changing JVM bytecodes
Rule: Do not add complexity to Java unless its usefulness outweighs its complexity
22 July 2019
University of Virginia CS 655

12. Our Solution: Java ParTy
Constructed JLS-extended syntax and semantics
Brief list of features:
type parameters within class or interface
where clause type constraints
type parameter can itself be of a parameterized type
22 July 2019
University of Virginia CS 655

13. University of Virginia CS 655
ParTy Code Example
class myClass<Type1, Type2>
where { boolean lt( Type1 t) }
extends myBaseClass implements myInterface {
// class body }
22 July 2019
University of Virginia CS 655

14. ParTy Implementation ParTy class A (1) Generic class A written
class A<T>{
// body }
(1) Generic class A written
(2) class B written to instantiate A with actual types
ParTy class B
Class B {
A<int> a;
A<String> b; }
22 July 2019
University of Virginia CS 655

15. ParTy Implementation ParTy class A (3) Classes are sent to compiler
(4) Corresponding .pclass created
ParTy compiler
class A<T>{
// body }
A.pclass
file
ParTy class B
Class B {
A<int> a;
A<String> b; }
B.pclass
file
22 July 2019
University of Virginia CS 655

16. ParTy Implementation ParTy class A
(5) Regular .class files generated at load-time
ParTy compiler
ParTy preprocessor
class A<T>{
// body }
A_int
.class
A.pclass
file
A_String
.class
ParTy class B
Class B {
A<int> a;
A<String> b; }
B.pclass
file
B.class
22 July 2019
University of Virginia CS 655

17. ParTy Implementation JVM (6) JVM-compatible classes are run
ParTy class A
ParTy compiler
ParTy preprocessor
class A<T>{
// body }
A_int
.class
JVM
A.pclass
file
A_String
.class
ParTy class B
Class B {
A<int> a;
A<String> b; }
B.pclass
file
B.class
22 July 2019
University of Virginia CS 655

18. Qualitative Evaluation
How useful is ParTy?
Constructed Pair, Set, LinkedList, OrderedSet generic classes
What restrictions are there?
No where clause for individual methods
no implicit type information allowed
no value parameters within <…>
22 July 2019
University of Virginia CS 655

19. Quantitative Evaluation
Code size
blowup delay is good for network transmissions
Benchmarking
Ran ParTy code against equivalent Java
Results...
22 July 2019
University of Virginia CS 655

20. Quantitative Evaluation: Results
ParTy yielded code up to 27.6% faster!
22 July 2019
University of Virginia CS 655

21. University of Virginia CS 655
Remaining Work
Finish ParTy compiler
add type checks
Support for primitive types
Integration of ParTy preprocessor into JVM ClassLoader
more extensive benchmarking
22 July 2019
University of Virginia CS 655

22. University of Virginia CS 655
Conclusion
22 July 2019
University of Virginia CS 655

23. University of Virginia CS 655
Conclusion
ParTy provides a powerful, safe, and efficient construct for designing generic classes without changing JVM bytecodes
ParTy code size expansion delayed until load time
ParTy adds only the most useful features of type parameterization to Java
22 July 2019
University of Virginia CS 655