[PDF] CSE 2221 - References - OSU CSE PDF 16.References.pdf

7 jan 2019 · OSU CSE 4 boolean char int double (plus 4 others) String XMLTree SimpleReader SimpleWriter NaturalNumber Reference Types

7 jan 2019 · The NaturalNumber component family allows you to manipulate natural numbers (i e , non-negative integers) – Unlike an int variable,

[PDF] CSE 2221 - References - OSU CSE

7 jan 2019 · OSU CSE 4 boolean char int double (plus 4 others) String XMLTree SimpleReader SimpleWriter NaturalNumber Reference Types

[PDF] CSE 2221 - Project 11 - Logan Frank

26 avr 2020 · setEnabled (for JButtons) and setText (for JText) are useful methods • Have the NaturalNumber documentation up while completing this project

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http://rise4fun com/Dafny SIGCSE 2013 OSU CSE 14 Dafny's int is considered unbounded, just like our NaturalNumber

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The Ohio State University, School of Environment and Natural Resources Fall Semester 2016 A number of guest speakers will also facilitate these kinds of

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the focus for group research term projects (Ohio State University Framework Plan , Sasaki Associates) At the end of the term, a select number of groups will earn

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Soon after Dr Ansley arrives, Dr Omkar Joshi, our new natural resource ulty with the increased number of recruitment events hosted by OSU and the College

[PDF] Natural Resources Advising Guide OSU-Cascades - Oregon State

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The Ohio State University's School of Natural Resources developed and implemented a resident There was no difference in stress level factors between the

References

7 January 2019OSU CSE1

Primitive vs. Reference Types

•Java types are divided into two different categories: -The built-in types are called primitive types •Includes boolean, char, int, double -All other types are called reference types(or class types •Includes String, XMLTree, SimpleReader,

SimpleWriter

, NaturalNumber, ...

7 January 2019OSU CSE2

Primitive vs. Reference Types

SimpleWriter

, NaturalNumber, ...

7 January 2019OSU CSE3

There is no limit on

the number of other user-defined types that can be developed.

Categories of Types, v. 1

7 January 2019OSU CSE4

boolean char int double (plus 4 others)String

XMLTree

...SimpleReaderSimpleWriter

NaturalNumber

Reference

TypesPrimitive

Types

Primitive vs. Reference Variables

•A primitive variable is a variable of a primitive type -This term is used sparingly in practice, and is introduced here for parsimony to distinguish a variable of a primitive type from... •A reference variable is a variable of a reference type

-A reference variable is fundamentally different from a primitive variable in ways that can dramatically impact how you reason about program behavior; beware!

7 January 2019OSU CSE5

Examples

7 January 2019OSU CSE6

true'y'133.14"Go"

Examples

7 January 2019OSU CSE7

true'y'133.14"Go"

Recall We Said Earlier...

7 January 2019OSU CSE8

This is a Stringvariable s

whose value is "Go", i.e., s = "Go" "Go" ... But Here's the "Real Picture"!

7 January 2019OSU CSE9

"Go" ... But Here's the "Real Picture"!

7 January 2019OSU CSE10

There is a Stringvariable

s , whose value is a referenceto an object whose value is "Go". "Go"

References and Objects

7 January 2019OSU CSE11

This is the references.

"Go"

References and Objects

7 January 2019OSU CSE12

This is the object s"points to"

or "refers to". "Go"

Reference and Object Values

•A reference variable like smay be considered to have either of two values: -The reference value of sin these pictures is the memory address at which the object is stored -The object value ofsin these pictures is the mathematical model value of the object the reference spoints to, in this case "Go"

7 January 2019OSU CSE13

Reference and Object Values

7 January 2019OSU CSE14

Think of the reference value as

simply an "id" or "serial number" of some place in memory.

Getting to the "Real Picture"

7 January 2019OSU CSE15

VariablesObjects

b c i d strue 22

192021222324

Getting to the "Real Picture"

7 January 2019OSU CSE16

VariablesObjects

b c i d strue 22

192021222324

This part of memory holds:

192021222324

... is indistinguishable in a program from this one. (Yet in

C or C++, you may do

calculations with these addresses/" id"sas if they were numbers! How crazy is that?)

Getting to the "Real Picture"

7 January 2019OSU CSE23

VariablesObjects

b c i d strue 23
19 20 21
22
23
24

Similarly, it is immaterial to the

program exactly where each variable is located in memory.

So We Can Simplify...

7 January 2019OSU CSE24

In our pictures, the

connection between the reference value of a reference variable and its object value is as an arrow.

Finally...

7 January 2019OSU CSE29

true 'y' 13 3.14 "Go"

Our pictures allow us to

abstract away even the fact that there are two parts of memory.

Notation

•We never care about writing down the reference value of a reference variable as a particular numerical value (though we draw a picture of it: an arrow out of a triangle) -So, if you see something like s = "Go"in a contract or a tracing table, it mustmean that the object value of sis the mathematical model value "Go"

Notation

•In a tracing table, however, we might want to remindourselves there is a reference involved, so we might record the value of variable susing a right arrow instead of an equals sign, e.g., s -This means that sis a reference variable whose object value is "Go" -Or: srefers to an object with value "Go" -Whywould we do this? Coming up...

7 January 2019OSU CSE31

The Assignment Operator

•The assignment operator =copiesthe value of the expression on the right-hand side into the variable on the left-hand side •For primitive types, "the value of" can mean only one thing •For reference types, it could mean "the referencevalue of" or "the object value of" -Which is it?

7 January 2019OSU CSE32

Assignment for Primitive Types

•Consider: inti= k + 7; -First, the expression k + 7is evaluated; say k = 3, so the expression evaluates to 10 -Next, the value 10is copied into i, so after the above statement has finished executing, we have i= 10 •How does this happen?

7 January 2019OSU CSE33

Step by Step: inti= k+ 7;

7 January 2019OSU CSE34

We already have k, a

whose value is 3.

Step by Step: inti= k + 7;

7 January 2019OSU CSE35

The intliteral is an

whose value is 7. 3

Step by Step: inti= k +7;

7 January 2019OSU CSE36

The intaddition

operator +results in another anonymous primitive variable whose value is 10. 310

Step by Step: inti= k + 7;

7 January 2019OSU CSE37

The declaration of the

intvariable iresults in an 310

Step by Step: inti=k + 7;

7 January 2019OSU CSE38

7310
10

The assignment

operator copies the value of the right- hand side into i.

Step by Step: inti= k + 7;

7 January 2019OSU CSE39

The temporary

anonymous primitive variables disappear now that the statement has completed executing. 3 10

A Tracing Table

7 January 2019OSU CSE40

CodeState

k = 3 int k = 3 i= 10

Assignment for Reference Types

•Consider:

String s = t + "

io -First, the expression t + "io"is evaluated; say t = "Oh", so the expression evaluates to "Ohio" -Next, the value "Ohio"is copied into s, so after the above statement has finished executing, we have s = "Ohio" •How does this happen?

7 January 2019OSU CSE41

Step by Step: String s = t+ "io";

7 January 2019OSU CSE42

"Oh"

We already have t, a

reference variable whose object value is "Oh".

7 January 2019OSU CSE43

"Oh""io"

The Stringliteral is

an anonymous reference variable whose object value is io

Step by Step: String s = t + "io";

7 January 2019OSU CSE44

"Oh""io""Ohio"

The Stringconcatenation

operator +results in another anonymous reference variable whose object value is "Ohio".

Step by Step: String s = t +"io";

7 January 2019OSU CSE45

"Oh" ?"io""Ohio"

The declaration of the

Stringvariable s

results in an uninitialized reference variable

Step by Step: String s= t + "io";

7 January 2019OSU CSE46

"Oh""io""Ohio"

The assignment

operator copies the reference valueon the right-hand side into s.

Step by Step: String s =t + "io";

7 January 2019OSU CSE47

"Oh""Ohio"

The temporary anonymous

reference variables disappear now that the statement has completed executing but the objectswith values "io"quotesdbs_dbs9.pdfusesText_15

[PDF] [PDF] CSE 2221 - References - OSU CSE

References

7 January 2019OSU CSE1

Primitive vs. Reference Types

SimpleWriter

7 January 2019OSU CSE2

Primitive vs. Reference Types

SimpleWriter

7 January 2019OSU CSE3

There is no limit on

Categories of Types, v. 1

7 January 2019OSU CSE4

XMLTree

NaturalNumber

Reference

TypesPrimitive

Primitive vs. Reference Variables

7 January 2019OSU CSE5

Examples

7 January 2019OSU CSE6

Examples

7 January 2019OSU CSE7

Recall We Said Earlier...

7 January 2019OSU CSE8

This is a Stringvariable s

7 January 2019OSU CSE9

7 January 2019OSU CSE10

There is a Stringvariable

References and Objects

7 January 2019OSU CSE11

This is the references.

References and Objects

7 January 2019OSU CSE12

This is the object s"points to"

Reference and Object Values

7 January 2019OSU CSE13

Reference and Object Values

7 January 2019OSU CSE14

Think of the reference value as

Getting to the "Real Picture"

7 January 2019OSU CSE15

VariablesObjects

192021222324

Getting to the "Real Picture"

7 January 2019OSU CSE16

VariablesObjects

192021222324

This part of memory holds:

 reference values ofreference

Getting to the "Real Picture"

7 January 2019OSU CSE17

VariablesObjects

192021222324

This part of memory holds:

Getting to the "Real Picture"

7 January 2019OSU CSE18

VariablesObjects

192021222324

Each object in memory has a

Getting to the "Real Picture"

7 January 2019OSU CSE19

VariablesObjects

192021222324

These numbers are the

Getting to the "Real Picture"

7 January 2019OSU CSE20

VariablesObjects

192021222324

The reference value of a

Getting to the "Real Picture"

7 January 2019OSU CSE21

VariablesObjects

192021222324

The reference value of a

Getting to the "Real Picture"

7 January 2019OSU CSE22

VariablesObjects

192021222324

C or C++, you may do

Getting to the "Real Picture"

reference values ofreference