1. CSE 1020:Programming by Delegation
Mark Shtern

2. Summary Java VM Edit-Compile-Run cycle Edit Compile Run Create or edit
Save
Compile
Run
Lunch main class
Interact with user

3. Summary
Math & Computer
Memory and Declaration

4. Delegation Delegating to a static Method Delegating to an Object
int width = 8; int height = 3; int area = width * height;
Delegating to a static Method
int area = Rectangle.area(8 , 3);
Delegating to an Object
Rectangle rectangle = new Rectangle(8,3);
int area = rectangle.getArea();

5. Client View Encapsulation, information hiding
A component can be improved without impact on client
feature
attribute
method
private
public = field
public
API- Application Programming Interface

6. Contracts Precondition - the client’s responsibility
Postcondition – the implementer’s responsibility

7. Example 01
Write a program that outputs the return of the getTime and toString methods of Date class whose UML diagram is shown below

8. Exercises 2.4
The following fragment uses a method in a class whose UML diagram is shown below.
Do you see any compile-time errors?
double amount = 2500;
Int period = 4;
double pay = Orbit.payBack(amount,period);

9. Exercises 2.5
The following fragment uses a method in a class whose UML diagram is shown below.
Do you see any compile-time errors?
int amount = 2500;
Int period = 4;
double pay = Orbit.payBack(amount,period);

10. Exercises 2.6
The following fragment uses a method in a class whose UML diagram is shown below.
Do you see any compile-time errors?
float amount = 2500;
Int period = 4;
double pay = Orbit.payBack(amount,period);

11. Exercises 2.7
The following fragment uses a method in a class whose UML diagram is shown below.
Do you see any compile-time errors?
double amount = 2500;
long period = 4;
double pay = Orbit.payback(amout,period);

12. Exercises 2.8
The following fragment uses a method in a class whose UML diagram is shown below.
Do you see any compile-time errors?
double amount = 2500;
int period = 4;
Int pay = Orbit.payback(amout,period);

13. Exercises 2.9
The following fragment uses a method in a class whose UML diagram is shown below.
Do you see any compile-time errors?
Bond.rating = ‘C’;
Bond.rate = 0.12;
double x = Bound.estimate();
output.println (Bound.inflate());

14. Exercises 2.10
The following fragment uses a method in a class whose UML diagram is shown below.
Do you see any compile-time errors?
Bond.rating = ‘C’;
Bond.rate = 0.12;
Bound.estimate();
Bound.inflate();

15. Summary Delegation Types and Casting Complexity Reduction
Static Method
Object Method
Types and Casting

16. Method Signature Return Visibility
name together with the types of parameters
sin(double)
getArea()
Return
Type such as void, double, int etc
Visibility
Private/Public

17. UML
Unified Modelling Language

18. Utility Class Utility Class all method are static
Utility Class may contains constant
UML
Attributes
Methods

19. Objects
Is a software entity that is capable of storing data as well as performing computations
Object has
Attributes
Methods
State
Reference

20. Object Features Rectangle rectangle = new Rectangle(4,5) Methods
Attributes
Rectangle rectangle = new Rectangle(4,5)
Class
reference
Instantiation

21. Class
Attributes
Attributes
Field
Private
Constructors
Methods
Methods

22. API
Complexity
Accountability
Substitutability

23. Software Engineering Patterns Risk Mitigation by Early Exposure
Handling Constants
Contracts
Precondition
Postcondition

24. 1020 Templet
Import java.util.Scanner Import java.io.PrintStream public class Templet { public static void main(String[] args) Scanner input = new Scanner (System.in); PrintStream output = System.out; .... }

25. I/O Input from keyboard Output on screen input.nextInt()
output.println()

26. Errors Compilation Errors Post-Compilation Errors Run-time Errors
Logical Errors

27. Post-Compilation Errors
Understand root of problem
Input
Location
Modify application
Verify solution
Re-test application

28. Debugging Techniques
Add print statements
Comment code

29. Exercises 2.12
The following fragment computes the average of three variables:
int x = 6/2;
int y = 12 / (x - 3);
int z = - 3;
double mean = x + y + z )/3;
It contains a compile-time, a runtime error and a logical error. Identify each.

30. Exercises 2.13
A Develop decided to declare 5/9 literal as a final and gave it the identifier SCALE_FACTOR
Which of the following declaration does not lead to a logical error
final double SCALE_FACTOR = 5 / 9;
final double SCALE_FACTOR = 5.0 / 9.0;
final double SCALE_FACTOR = 5 / 9.0;
final double SCALE_FACTOR = (double)(5 / 9);
final double SCALE_FACTOR = (double) 5/ 9;
final double SCALE_FACTOR = 5/(double)9;

31. Exercises 2.14
Rewrite the following fragment so that it is free of magic numbers:
output.println (“Enter speed in km/h”);
double speed = input.nextDouble();
speed = speed * 1000 / 3600;
output.println (“Enter speed in ft”);
double distance = distance * ;
double time = distance/speed;