1. COS 260 DAY 15
Tony Gauvin

2. Agenda Assignment 5 will be posted soon Questions?
Assignment 3 Over Due
Assignment 4 posted
Due 0ct 31
Assignment 5 will be posted soon
Mini-quiz Six today
Chapter 7
30 min
Password “JohnvonNeumann”
Mini-Quiz 7
Friday Oct 27
Chap 8
Finish Designing classes

3. Capstone Project Capstone Project Description Fall 2017.pdf
October Proposal Due ed to Tony in Blackboard
October 27 Progress Report ed to Tony in Blackboard
November 16 Progress Report ed to Tony in Blackboard
November Progress Report ed to Tony in Blackboard
December All Deliverables & Presentation Due
Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

4. Review Explain & Discuss Cohesion Coupling Code Duplications
Responsibility-driven design
Localizing Change
Implicit Coupling
Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

5. Thinking ahead
When designing a class, we try to think about changes likely to be made in the future.
We aim to make those changes easy.
Requires a little more effort now to greatly reduce effort later.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

6. Refactoring When classes are maintained code is usually added.
Classes and methods tend to become longer.
Every now and then, classes and methods should be refactored to maintain cohesion and low coupling.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

7. An exercise in the need for refactoring
Start with Zuul-better
See on page
Add item to rooms
One item for room
One item for player
Add more items to room and player
Player limited by weight
Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

8. Refactoring and testing
When refactoring code, separate the refactoring from making other changes.
First do the refactoring only, without changing the functionality.
Test before and after refactoring to ensure that nothing was broken.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

9. Design questions Common questions:
How long should a class be?
How long should a method be?
These can now be answered in terms of cohesion and coupling.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

10. Design guidelines
A method is too long if it does more then one logical task.
A class is too complex if it represents more than one logical entity.
Note: these are guidelines - they still leave much open to the designer.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

11. Enumerated Types A language feature.
Uses enum instead of class to introduce a type name.
Their simplest use is to define a set of significant names.
Alternative to static int constants.
When the constants’ values would be arbitrary.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

12. A basic enumerated type
public enum CommandWord {
// A value for each command word,
// plus one for unrecognised commands.
GO, QUIT, HELP, UNKNOWN; }
Each name represents an object of the enum type, e.g., CommandWord.HELP.
Enum objects are not created directly.
Enum definitions can also have fields, constructors and methods.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

13. The Switch Statement
switch (something) {
case valueofsomething:
java statement;
break;
break:
default: }
Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

14. Review Programs are continuously changed.
It is important to make this change possible.
Quality of code requires much more than just performing correct at one time.
Code must be understandable and maintainable.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

15. Review
Good quality code avoids duplication, displays high cohesion, low coupling.
Coding style (commenting, naming, layout, etc.) is also important.
There is a big difference in the amount of work required to change poorly structured and well structured code.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

16. Objects First with Java
Well-behaved objects
6.0
© David J. Barnes and Michael Kölling

17. Main concepts to be covered
Objects First with Java
Main concepts to be covered
Testing
Debugging
Test automation
Writing for maintainability
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

18. Objects First with Java
Code snippet of the day
public void test() { int sum = 1; for (int i = 0; i <= 4; i++); sum = sum + 1; } System.out.println("The result is: " + sum); System.out.println("Double result: " + sum+sum);
What is the output?
The result is: 2
Double result: 22
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

19. Objects First with Java
Possible results
Which is printed?
The result is: 5
The result is: 6
The result is: 11
The result is: 2
Double result: 22
The result is: 2
Double result: 12
Double result: 4
Double result: 22
Double result: 66
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

20. Objects First with Java
Code snippet of the day
public void test() { int sum = 1; for (int i = 0; i <= 4; i++); sum = sum + 1; } System.out.println("The result is: " + sum); System.out.println("Double result: " + sum+sum);
The result is: 2
Double result: 22
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

21. We have to deal with errors
Objects First with Java
We have to deal with errors
Early errors are usually syntax errors.
The compiler will spot these.
Later errors are usually logic errors.
The compiler cannot help with these.
Also known as bugs.
Some logical errors have no immediately obvious manifestation.
Commercial software is rarely error free.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

22. Prevention vs Detection (Developer vs Maintainer)
We can lessen the likelihood of errors:
Use software engineering techniques, like encapsulation.
Pay attention to cohesion and coupling.
We can improve the chances of detection:
Use software engineering practices, like modularization and good documentation.
We can develop detection skills.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

23. Objects First with Java
Testing and debugging
These are crucial skills.
Testing searches for the presence of errors.
Debugging searches for the source of errors.
The manifestation of an error may well occur some ‘distance’ from its source.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

24. Testing and debugging techniques
Objects First with Java
Testing and debugging techniques
Unit testing (within BlueJ)
Test automation
Manual walkthroughs
Print statements
Debuggers
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

25. Objects First with Java
Unit testing
Each unit of an application may be tested.
Method, class, module (package in Java).
Can (should) be done during development.
Finding and fixing early lowers development costs (e.g. programmer time).
A test suite is built up.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

26. Objects First with Java
Testing fundamentals
Understand what the unit should do – its contract.
You will be looking for violations.
Use positive tests and negative tests.
Test boundaries.
Zero, One, Full.
Search an empty collection.
Add to a full collection.
Search for/remove the only element.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

27. Objects First with Java Test automation
Well-behaved objects
Test automation
© David J. Barnes and Michael Kölling

28. Main concepts to be covered
Unit testing
JUnit
Regression testing
Test cases
Test classes
Assertions
Fixtures
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

29. Unit testing within BlueJ
Objects First with Java
Unit testing within BlueJ
Objects of individual classes can be created.
Individual methods can be invoked.
Inspectors provide an up-to-date view of an object’s state.
Explore through the online-shop project.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

30. Demo of online-shop

31. Objects First with Java
Test automation
Good testing is a creative process, but ...
... thorough testing is time consuming and repetitive.
Regression testing involves re-running tests.
Use of a test rig or test harness can relieve some of the burden.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

32. Test harness
Additional test classes are written to automate the testing.
Objects of the harness classes replace human interactivity.
Creativity and imagination required to create these test classes.
Test classes must be kept up to date as functionality is added.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

33. Objects First with Java
Test automation
Test frameworks exist to support automation.
Explore fuller automation through the online-shop-junit project.
Intervention only required if a failure is reported.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

34. Demo of online-shop-junit
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

35. JUnit JUnit is a Java test framework
Test cases are methods that contain tests
Test classes contain test methods
Assertions are used to assert expected method results
Fixtures are used to support multiple tests
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

36. Well-behaved objects
Debugging

37. Prevention vs Detection (reprise)
We can lessen the likelihood of errors:
Use software engineering techniques, like encapsulation.
Pay attention to cohesion and coupling.
We can improve the chances of detection:
Use software engineering practices, like modularization and good documentation.
We can develop detection skills.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

38. Debugging techniques Manual walkthroughs Print statements Debuggers
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

39. Modularization and interfaces
Objects First with Java
Modularization and interfaces
Applications often consist of different modules:
E.g. so that different teams can work on them.
The interface between modules must be clearly specified.
Supports independent concurrent development.
Increases the likelihood of successful integration.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

40. Modularization in a calculator
Objects First with Java
Modularization in a calculator
Each module does not need to know implementation details of the other.
User controls could be a GUI or a hardware device.
Logic could be hardware or software.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

41. Method headers as an interface
Objects First with Java
Method headers as an interface
// Return the value to be displayed.
public int getDisplayValue();
// Call when a digit button is pressed.
public void numberPressed(int number);
// Plus operator is pressed.
public void plus();
// Minus operator is pressed.
public void minus();
// Call to complete a calculation.
public void equals();
// Call to reset the calculator.
public void clear();
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

42. Objects First with Java
Debugging
It is important to develop code-reading skills.
Debugging will often be performed on others’ code.
Techniques and tools exist to support the debugging process.
Explore through the calculator-engine project.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

43. Objects First with Java
Manual walkthroughs
Relatively underused.
A low-tech approach.
More powerful than appreciated.
Get away from the computer!
‘Run’ a program by hand.
High-level (Step) or low-level (Step into) views.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

44. Tabulating object state
Objects First with Java
Tabulating object state
An object’s behavior is largely determined by its state …
… so incorrect behavior is often the result of incorrect state.
Tabulate the values of key fields.
Document state changes after each method call.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

45. Objects First with Java
Verbal walkthroughs
Explain to someone else what the code is doing:
They might spot the error.
You might spot the error, through the process of explaining.
Group-based processes exist for conducting formal walkthroughs or inspections.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

46. Objects First with Java
Print statements
The most popular technique.
No special tools required.
All programming languages support them.
Only effective if the right methods are documented.
Output may be voluminous!
Turning off and on requires forethought.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

47. Choosing a test strategy
Objects First with Java
Choosing a test strategy
Be aware of the available strategies.
Choose strategies appropriate to the point of development.
Automate whenever possible.
Reduces tedium.
Reduces human error.
Makes (re)testing more likely.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

48. Objects First with Java
Debuggers
Debuggers are both language- and environment-specific.
BlueJ has an integrated debugger.
Support breakpoints.
Step and Step-into controlled execution.
Call sequence (stack).
Object state.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling

49. Debugging streams (advanced)
A pipeline of multiple operations might be hard to debug.
The peek operation can provide insights.
Consumer that passes on its input unchanged; e.g.: peek(s -> System.out.println(s))
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.

50. Objects First with Java
Review
Errors are a fact of life in programs.
Good software development techniques can reduce their occurrence.
Testing and debugging skills are essential.
Make testing a habit.
Automate testing where possible.
Continually repeat tests.
Practice a range of debugging skills.
© 2017 Pearson Education, Inc. Hoboken, NJ. All rights reserved.
© David J. Barnes and Michael Kölling