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CSE115 / CSE503 Introduction to Computer Science I Dr. Carl Alphonce 343 Davis Hall [email protected] Office hours: Tuesday 10:00 AM – 12:00 PM * Wednesday 4:00 PM – 5:00 PM Friday 11:00 AM – 12:00 PM OR request appointment via e-mail * Tuesday adjustments: 11:00 AM – 1:00 PM on 10/11, 11/1 and 12/6

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Page 1: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

CSE115 / CSE503Introduction to Computer Science I

Dr. Carl Alphonce343 Davis Hall

[email protected]

Office hours:Tuesday 10:00 AM – 12:00 PM*

Wednesday 4:00 PM – 5:00 PMFriday 11:00 AM – 12:00 PM

OR request appointment via e-mail*Tuesday adjustments: 11:00 AM – 1:00 PM on 10/11, 11/1 and 12/6

Page 2: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

© Dr. Carl Alphonce

ANNOUNCEMENTS

Page 3: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

EXAM

RES

ULT

S (F

A15)

0

20

40

60

80

100

120

140

10 20 30 40 50 60 70 80 90 100

MAX 100 (x19 = 3.4%)MEDIAN 68MEAN 68.4MIN 20

N = 577

Page 4: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

EXAM

RES

ULT

S (S

P16)

MAX 100 (x13 = 4.2%)MEDIAN 76MEAN 74.3MIN 8

N = 320

0

10

20

30

40

50

60

70

80

[0,10) [10,20) [20,30) [30,40) [40,50) [50,60) [60,70) [70,80) [80,90) [90,100]

CSE115 Exam 1 Grade Distribution

Page 5: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

0

20

40

60

80

100

120

140

160

180

[0,10) [10,20) [20,30) [30,40) [40,50) [50,60) [60,70) [70,80) [80,90) [90,100]

CSE115 Exam 1 Grade Distribution

EXAM

RES

ULT

S (F

A16)

MAX 100 (x15 = 2.5%)MEDIAN 76MEAN 74.4MIN 16

N = 626

Page 6: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

© Dr. Carl Alphonce

ELECTRONICS:off & away

Page 7: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

ROAD

MAP

Last timeModeling: sharing association

TodayModeling: exclusive associationnull

Coming upInterfacesRealization relationship

© Dr. Carl Alphonce

Page 8: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

© Dr. Carl Alphonce

REVIEW

Page 9: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

The

clas

s de

finiti

onpublic class Shape {

private java.awt.Color _color;public Shape(java.awt.Color c) {

_color = c;}

public java.awt.Color getColor() {

return _color;}

public void setColor(java.awt.Color c){_color = c;

}}

Page 10: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

stat

ic v

aria

bles

/ ja

va.a

wt.C

olor

Shape s1 = new Shape(java.awt.Color.BLUE);Shape s2 = new Shape(java.awt.Color.RED);s2.setColor(s1.getColor());

What are the highlighted expressions?

Page 11: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

Exer

cise

Shape s1 = new Shape(java.awt.Color.BLUE);

Shape s2 = new Shape(java.awt.Color.RED);s2.setColor(s1.getColor());

Discuss with your neighbors what happens.

What will the object diagram look like after the method calls happen?

Page 12: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

s2s1 = new Shape(java.awt.Color.BLUE)

Color object

Color.BLUE

STACK HEAP STATIC

Color object

Color.RED

s1

Page 13: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

s2s1 = new Sh

ape(java

.awt.Col

or.BLUE)

Color object

Color.BLUE

STACK HEAP STATIC

Color object

Color.RED

s1

Shape object

_color

(1) Allocate space for Shapeobject, and then …

Page 14: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

s2s1 = new Sh

ape(java

.awt.Col

or.BLUE)

Color object

Color.BLUE

STACK HEAP STATIC

Color object

Color.RED

s1

Shape object

_color

this

c

(2) … call constructor (creating invocation record on stack)

and initialize parameters (including the implicit ‘this’)…

Page 15: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

s2s1 = new Sh

ape(java

.awt.Col

or.BLUE)

Color object

Color.BLUE

STACK HEAP STATIC

Color object

Color.RED

s1

Shape object

_color

this

c

(3) … run code in constructor body:this._color = c

to initialize the _color instance variable.

Page 16: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

s2s1 = new Sh

ape(java

.awt.Col

or.BLUE)

Color object

Color.BLUE

STACK HEAP STATIC

Color object

Color.RED

s1

Shape object

_color

(4) When constructor call is finished its

invocation is removed from the runtime

stack, and a reference to the object is stored

in s1

Page 17: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

BEF

OR

E The next slide shows the “before” object diagram that you and your

neighbors should have come up with.

Page 18: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

s2

Befo

re c

all:

s2.setColor(s1.getColor())

Color object

Color.BLUE

STACK HEAP STATIC

Color object

Color.RED

s1

Shape object

_color

Shape object

_color

Page 19: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

s2

At c

all e

ntry

: s2.setColor(s1.getColor())

Color object

Color.BLUE

STACK HEAP STATIC

Color object

Color.RED

s1

Shape object

_color

Shape object

_color

returnedvalue

this

Page 20: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

s2

At c

all e

xit:

s2.setColor(s1.getColor())

Color object

Color.BLUE

STACK HEAP STATIC

Color object

Color.RED

s1

Shape object

_color

Shape object

_color

returnedvalue

this

Page 21: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

s2

The

retu

rned

val

ue is

hel

d in

a te

mpo

rary

: s2.setColor(s1.getColor())

Color object

Color.BLUE

STACK HEAP STATIC

Color object

Color.RED

s1

Shape object

_color

Shape object

_color

The returned value may be stored in a register.

Page 22: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

s2

At c

all e

ntry

: s2.setColor(s1.getColor())

Color object

Color.BLUE

STACK HEAP STATIC

Color object

Color.RED

s1

Shape object

_color

Shape object

_color

this

c

Page 23: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

s2

At c

all e

xit:

s2.setColor(s1.getColor())

Color object

Color.BLUE

STACK HEAP STATIC

Color object

Color.RED

s1

Shape object

_color

Shape object

_color

this

c

Page 24: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

AFTE

R The next slide shows the “after” object diagram that you and your neighbors

should have come up with.

Page 25: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

s2

Afte

r cal

l exi

t: s2.setColor(s1.getColor())

Color object

Color.BLUE

STACK HEAP STATIC

Color object

Color.RED

s1

Shape object

_color

Shape object

_color

Page 26: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

Resu

lt?

Both shapes have the same color (java.awt.Color.BLUE).

This is OK.

Page 27: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

© Dr. Carl Alphonce

MOVING ON

Page 28: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

© Dr. Carl Alphonce

MODELING(also: execution model)

EXERCISE

Page 29: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

Now

con

side

r thi

s sc

enar

io:

Dog fido = new Dog(new Collar());Dog dino = new Dog(new Collar());

Page 30: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

dino

Dog dino

= new Dog(new Collar());

Dog fido

= new Dog(new Collar());

Collar object

STACK HEAP STATIC

Collar object

fido

Dog object

_collar

Dog object

_collar

Page 31: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

Exer

cise

Dog fido = new Dog(new Collar());Dog dino = new Dog(new Collar());dino.setCollar(fido.getCollar());

This example has *exactly* the same structure as our Shape-Color example.

Consider what happens in the object diagram. Run through it with your neighbors. Make sure you understand it!

Does it make sense?

Page 32: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

dino

Befo

re c

all:

dino.setCollar(fido.getCollar())

Collar object

STACK HEAP STATIC

Collar object

fido

Dog object

_collar

Dog object

_collar

Page 33: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

dino

Afte

r cal

l: dino.setCollar(fido.getCollar())

Collar object

STACK HEAP STATIC

Collar object

fido

Dog object

_collar

Dog object

_collar

Page 34: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

Resu

lt?

Both dogs have the same collar.

Two objects can sensibly share the color blue,but two dogs cannot sensibly share a single collar.

Aside: the second collar is “lost”, since we no longer have a reference to it. When we no longer maintain any reference to an object it becomes eligible for garbage collection.

Page 35: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

© Dr. Carl Alphonce

null

Page 36: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

Wha

t cou

ld w

e do

inst

ead? Try to express what the basic problem is, and

what we could do instead, in plain English.

Page 37: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

‘nul

l’‘null’ denotes the null reference, a reference which does not refer to any object.

There is also a special null type, the type of the expression null which has no name. Because the null type has no name, it is impossible to declare a variable of the null type or to cast to the null type. The null reference is the only possible value of an expression of null type. The null reference can always undergo a widening reference conversion to any reference type.In practice, the programmer can ignore the null type and just pretend that null is merely a special literal that can be of any reference type.

https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html

We can use ‘null’ to solve the two dogs, one collar problem (see code on next slide).

Page 38: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

rem

oveC

olla

rrat

her t

han

getC

olla

rpublic class Dog {

private Collar _collar;public Dog(Collar collar) {

this._collar = collar;}public void setCollar(Collar collar) {

this._collar = collar;}public Collar removeCollar() {

Collar temp = this._collar;this._collar = null;

return temp;}

}

Page 39: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

Can

als

o us

e in

con

stru

ctor

public class Dog {private Collar _collar;public Dog() {

_collar = null;}public void setCollar(Collar collar) {

_collar = collar;}public Collar removeCollar() {

Collar temp = _collar;_collar = null;

return temp;}

}

Now a Dog can be created without a

Collar

Page 40: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

dino

Befo

re c

all:

dino.setCollar(fido.removeCollar())

Collar object

STACK HEAP STATIC

Collar object

fido

Dog object

_collar

Dog object

_collar

Page 41: CSE115 / CSE503 Introduction to Computer Science …...‘null’ denotes the null reference, a reference which does not refer to any object. There is also a special null type, the

dino

Afte

r cal

l: dino.setCollar(fido.removeCollar())

Collar object

STACK HEAP STATIC

Collar object

fido

Dog object

_collar

Dog object

_collar

A variable whose value is null can be denoted by a box

with ‘null’ written in, or a box with a diagonal line through it.


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CSE115 / CSE503 Introduction to Computer Science I Dr. Carl Alphonce 343 Davis Hall [email protected] 1

CSE115 / CSE503 Introduction to Computer Science I Dr ... · Introduction to Computer Science I Dr. Carl Alphonce 343 Davis Hall [email protected] Office hours: Tuesday 10:00 AM

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of salaries PST... · Ghulam Nabi Mugheri Ghulam Nabi Sabz Ali Chandio Ali Hassan Chandio RAMESH BAHAR I Al Ayas Hussain Pa than null null null null null null null nell null RAWATI