Design by Contract using Jose

1. Design by Contractusing Jose Ohad Barzilay April 2004, IDC

2. About Jose • A Design by Contract tool written for java • Still in ALFA status • Similar tools: • iContract • JContract • JMSAssert • JML

3. More About Jose • Uses AspectJ • Uses Doclet • Uses ANTLR

4. Getting Jose • For the use of this course students only and only for academic purposes • Command line configuration or as an IDE external tool • Executable jar • Get it this weekend from the course discussion group

5. Stack with Assertions (1) class STACK1 [G] feature -- Access count: INTEGER -- Number of stack elements item: G is -- Top element require not empty do ... end

6. Stack with Assertions (1) publicclassStack1 { publicintcount() { returnelements.size(); } /** *@require!empty(),"NotEmpty" */ publicObjectitem() { returnelements.firstElement(); } protectedVectorelements=null; }

7. Stack with Assertions (2) feature -- Status report empty: BOOLEAN is -- Is stack empty? do ...end full: BOOLEAN is -- Is stack representation full? do ...end

8. Stack with Assertions (2) publicbooleanempty() { returncount()==0; } publicbooleanfull() { returnelements.capacity()==count(); }

9. Stack with Assertions (3) feature -- Element change put (x: G) is -- Add x on top. require not full do ... ensure not empty item = x count = old count + 1 end

10. Stack with Assertions (3) /** *@require!full(),"NotFull" *@ensure!empty(),"NotEmpty" *@ensureitem()==x,"item()equalsx" *@ensurecount()==$prev(count())+1, *"count()incremented" */ publicvoidput(Objectx) { elements.add(0,x); }

11. Stack with Assertions (4) remove is -- Remove top element. require not empty do ... ensure not full count = old count – 1 end end

12. Stack with Assertions (4) /** *@require!empty(),"NotEmpty" *@ensure!full(),"NotFull" *@ensurecount()==$prev(count())-1, * "count()decremented" */ publicvoidremove() { elements.remove(0); }

13. Class level Assertions (5) /** *@invariantelements.size()>=0, * "nonnegativesize" */ publicclassStack1 { ... }

14. Jose keywords • Precondition • @precondition • @pre • @ require • Postcondition • @ postcondition • @ post • @ ensure • Invarinat • @ invarinat • @ inv

15. Jose keywords • Return value • $ret • Old value • $prev(<expr>) • $prev(<type>;<expr>)