CSE 1020:Programming by Delegation Mark Shtern

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

Summary Math & Computer Memory and Declaration

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();

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

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

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

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);

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);

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);

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);

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);

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());

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();

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

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

UML Unified Modelling Language

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

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

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

Class Attributes Attributes Field Private Constructors Methods Methods

API Complexity Accountability Substitutability

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

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; .... }

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

Errors Compilation Errors Post-Compilation Errors Run-time Errors Logical Errors

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

Debugging Techniques Add print statements Comment code

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.

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;

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 * 0.3048; double time = distance/speed;