CS 151: Object-Oriented Design October 29 Class Meeting Department of Computer Science San Jose State University Fall 2013 Instructor: Ron Mak mak.

CS 151: Object-Oriented Design October 29 Class Meeting

Department of Computer ScienceSan Jose State University

Fall 2013Instructor: Ron Mak

www.cs.sjsu.edu/~mak

http://www.cs.sjsu.edu/~mak

http://www.cs.sjsu.edu/~mak

SJSU Dept. of Computer ScienceFall 2013: October 29

CS 151: Object-Oriented Design© R. Mak

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Midterm Results

Median 75.0Mean 76.7Standard deviation 12.1



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Unofficial Field Trip Computer History Museum in Mt. View

http://www.computerhistory.org/

Saturday, December 7, 11:30 – closing time Special free admission. Do a self-guided tour of the new Revolution exhibit. See a life-size working model of Charles Babbage’s

Difference Engine in operation, a hand-cranked mechanical computer designed in the early 1800s.

Experience a fully restored IBM 1401 mainframe computer from the early 1960s in operation. General info: http://en.wikipedia.org/wiki/IBM_1401 My summer seminar: http://www.cs.sjsu.edu/~mak/1401/ Restoration:

http://ed-thelen.org/1401Project/1401RestorationPage.html

http://www.computerhistory.org/

http://en.wikipedia.org/wiki/IBM_1401

http://www.cs.sjsu.edu/~mak/1401/

http://ed-thelen.org/1401Project/1401RestorationPage.html



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Unofficial Field Trip The new Revolution exhibit is now open!

Walk through a timeline of the First 2000 Years of Computing History.

Historic computer systems, data processing equipment, and other artifacts.

Small theater presentations.

Atanasoff-Berry Computer

HollerithCensus

Machine



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Unofficial Field Trip Babbage Difference Engine,

fully operational Hand-cranked mechanical

computer. Computed polynomial

functions. Designed by Charles Babbage

in the early to mid 1800s. Arguably the world’s first

computer scientist, lived 1791-1871.

He wasn’t able to build it because he lost his funding.

Live demo at 1:30 His plans survived and this

working model was built. Includes a working printer!http://www.computerhistory.org/babbage/

http://www.computerhistory.org/babbage/



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Unofficial Field Trip IBM 1401 computer, fully restored and operational

A small transistor-based mainframe computer. Extremely popular with small businesses in the late 1950s

through the mid 1960s Maximum of 16K bytes of memory. 800 card/minute card reader (wire brushes). 600 line/minute line printer (impact). 6 magnetic tape drives, no disk drives.



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Extra Credit! There will be extra credit if you participate in the visit

to the Computer History Museum. Complete a Canvas quiz whose answers are to be found

among the museum exhibits and presentations. Up to n points added to your midterm score.

n = the number of quiz questions_



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Team Exercise: UML Class Diagram A company has a manufacturing division and a research division. The company has a president and two vice presidents.

One VP runs manufacturing and the other runs research. Each division has employees other than its VP,

and it might also have an administrative assistant. All manufacturing workers are union members, but none of the

researchers. All of the researchers have college degrees, as do some of the manufacturing employees.

Each employee is paid either by the hour, biweekly, or monthly. Manufacturing workers can get overtime pay, but not researchers. All employees except the president and vice presidents can get bonuses.

The company manufactures different products, three of which are widgets, gadgets, and gizmos. A gadget can be sold separately, or several can be bundled with a widget. A gizmo can only be sold as part of a gadget.

The researchers are working on projects to improve the company’s existing products or to design new products.



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An Exercise Solution

Vice President

AdministrativeAssistant

0..1

Research

Manufacturing

Division

Company

CollegeDegree

President

«interface»Overtime

Pay

«interface»Union

Member

Product *

0..1

Gizmo

Gadget

Widget

«interface»Bonus

Employee

<<enumeration>>Pay

HourlyBiweeklyMonthly

*

*

Worker*

Researcher*Project

New product



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Inheritance By now, inheritance should be a familiar concept.

From: Object-Oriented Design & Patterns, John Wiley & Sons, 2006.



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Manager extends Employeepublic class Employee{ public Employee(String aName) { name = aName; } public void setSalary(double aSalary) { salary = aSalary; } public String getName() { return name; } public double getSalary() { return salary; }

private String name; private double salary;}

public class Manager extends Employee{ public Manager(String aName) { ... } public void setBonus(double aBonus) { bonus = aBonus; } // new method public double getSalary() { ... } // overrides Employee method

private double bonus; // new field}

What are the differences betweenManager and Employee?



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Superclasses and Subclasses Employee is the superclass

Manager is the subclass

A manager “is a” employee.

A manager is a specialized type of employee.

The set of Manager objects is a subset of the set of Employee objects._




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Class Hierarchies AKA inheritance hierarchies In the real world, hierarchies express

general/specific relationships among concepts. The most general concept is at the root of a tree. More specific concepts are children. The most specific concepts are leafs.

Object-oriented programming uses class hierarchies. The most general superclass is at the root of a tree. More specific subclasses are children. The most specific subclasses are leafs.

Class hierarchies can be complex. But they shouldn’t be.



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Class Hierarchies




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Class Hierarchies




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The Liskov Substitution Principle Named after Barbara Liskov

MIT computer science professor Pioneer in object-oriented programming

In your Java code, you should be able to substitute a superclass object by a subclass object:

Employee e = new Employee("John Doe");System.out.println("salary = " + e.getSalary());

Superclass

Employee e = new Manager("Mary Jane");System.out.println("salary = " + e.getSalary());

Subclass



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The Liskov Substitution Principle

The type of variable e is EmployeeThe type of the object is Manager. How does Java know which getSalary() method

to invoke at run time? The JVM uses the type of the object,

not the type of the variable. Polymorphism

How is the Liskov Substitution Principle related to the principle of Programming to the Interface? The type of variable e is the superclass Employee instead of

the more specific subclass type Manager.

Employee e = new Manager("Mary Jane");System.out.println("salary = " + e.getSalary());

CS 151: Object-Oriented Design October 29 Class Meeting Department of Computer Science San Jose State University Fall 2013 Instructor: Ron Mak mak.

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