CSE 1020:Programming by DelegationMark Shtern

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Summary

• Java VM• Edit-Compile-Run cycle

– Edit• Create or edit• Save

– Compile– Run

• Lunch main class• Interact with user

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Summary

• Math & Computer• Memory and Declaration

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Delegation

int width = 8;int height = 3;int area = width * height;

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Delegating to a static Method int area = Rectangle.area(8 , 3);

Delegating to an ObjectRectangle rectangle = new Rectangle(8,3);

int area = rectangle.getArea();

Client View• Encapsulation, information hiding • A component can be improved without impact

on client

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feature

attribute

method

private

public = field

public

private

• 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

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Exercises 2.4

• The following fragment uses a method in a class whose UML diagram is shown below.

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• 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.

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• 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.

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• 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.

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• 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.

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• 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.

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• 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.

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• Do you see any compile-time errors?

Bond.rating = ‘C’;Bond.rate = 0.12;

Bound.estimate();Bound.inflate();

Summary

• Delegation– Complexity Reduction– Static Method– Object Method

• Types and Casting

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Method

• Signature– name together with the types of parameters sin(double) getArea()

• Return– Type such as void, double, int etc

• Visibility– Private/Public

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UML

• Unified Modelling Language

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Utility Class

• Utility Class all method are static• Utility Class may contains constant• UML

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Attributes

Methods

Objects

• Is a software entity that is capable of storing data as well as performing computations

• Object has– Attributes– Methods– State– Reference

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Object

• Features– Methods– Attributes

Rectangle rectangle = new Rectangle(4,5)

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Class reference

Instantiation

Class

• Attributes– Field– Private

• Constructors• Methods

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Attributes

Methods

API

• Complexity• Accountability• Substitutability

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Software Engineering

• Patterns• Risk Mitigation by Early Exposure• Handling Constants• Contracts

– Precondition– Postcondition

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1020 TempletImport java.util.ScannerImport java.io.PrintStream

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

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I/O

• Input from keyboard input.nextInt()

• Output on screenoutput.println()

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Errors

• Compilation Errors• Post-Compilation Errors

– Run-time Errors– Logical Errors

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Post-Compilation Errors

• Understand root of problem– Input– Location

• Modify application• Verify solution• Re-test application

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Debugging Techniques

• Add print statements• Comment code

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Exercises 2.12

• The following fragment computes the average of three variables:

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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

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a. final double SCALE_FACTOR = 5 / 9;b. final double SCALE_FACTOR = 5.0 / 9.0;

c. final double SCALE_FACTOR = 5 / 9.0;

d. final double SCALE_FACTOR = (double)(5 / 9);

e. final double SCALE_FACTOR = (double) 5/ 9;

f. final double SCALE_FACTOR = 5/(double)9;

Exercises 2.14

• Rewrite the following fragment so that it is free of magic numbers:

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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;