clase 02- programacion orientada a objetos java ii

8/10/2019 Clase 02- Programacion Orientada a Objetos Java II

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Creating Your OwnCreating Your Own

ClassesClasses

Sang ShinSang ShinMichle GarocheMichle Garoche

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Defining YourDefining YourOwn ClassOwn Class


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Defining your own classes

Things to take note of for the snta! defined in thissection:

" # or more occurrences of theline where it was applied to$

%description& substitute an actual value forthis part instead of tping it as it is$

' this part is optional


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Defining your own classes

To define a class, we write:

class {

*

*

*

} where

%modifier& is an access modifier, which ma be combined withother tpes of modifier$


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Example: Define StudentRecord

Classpublic class StudentRecord{

//we'll add more code here later

}

where, public means that our class is accessible to other classes

outside the package

class this is the keword used to create a class in *ava

+tudentecord a uni-ue identifier that describes ourclass


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Coding uidelines

Think of an appropriate name for our class$ Don.t /ustcall our class 012 or an random names ou can thinkof$

Class names starts with a CA34TA5 letter not are-uirement, however$

The file name of our class must have the +A67 8A67as our class name$

+tudentecord class should be defined in +tudentecord$/ava


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Demo:Demo:

Exercise !: Create your classExercise !: Create your class!"!#$javase$createclass%&ip!"!#$javase$createclass%&ip


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Class (ariables

;or e!ample,


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'nstance (ariables'nstance (ariables


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Declaring *roperties ),ttributes+

To declare a certain attribute for our class, we write,

[


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'nstance (ariables

public class StudentRecord { // Instance variables

pri"ateString name;pri"ateString address;pri"ateint age;pri"atedouble mathGrade;pri"atedouble englishGrade;pri"atedouble scienceGrade;pri"atedouble average;//we'll add more code here later

}

where,

privatehere means that the variables are onl accessible withinthe class$


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Coding uidelines for 'nstance(ariables

Declare all our instance variables right after >publicclass 6class ?>

Declare one variable for each line$

4nstance variables, like an other variables should startwith a small letter$

Use an appropriate data tpe for each variable oudeclare$ (mandator)

Declare instance variables as private so that onlmethods in the same class can access them directl$

7ncapsulation


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Static (ariablesStatic (ariables


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Static )Class+ variables

public class StudentRecord {

// static "ariables

pri"ate staticint student%ount$

// we'll add more code here later}

we use the keword static to indicate that a variable is astatic (class) variable$


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-et.ods-et.ods


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Example /: ,ccessor )etter+ -et.od


pri"ate Strin) name$

// some code

// n e0ample in which the business lo)ic is

// used to return a "alue on an accessor method

public double )et"era)e({

double result 1$

resultmath2rade3en)lish2rade3science2rade(/4$return result$

}

}


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-utator )Setter+ -et.ods

6utator 6ethods

used to write or change values of a variable

Usuall written as:

set


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Example: -utator )Setter+ -et.od


private String name;

:

public "oid setame Strin) temp ({name = temp;

}}

where,

public means that the method can be called from ob/ects ofother classes

void means that the method does not return an value set8ame the name of the method

(+tring temp) parameter that will be used inside our method


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Example: -ultiple returnstatements

public Strin) )etumber,n5ords int num ({

Strin) defaultum 67ero6$

if num 8 ({

return 6one6$

}

else if num 9({

return 6two6$

}

return defaultum$}


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Static -et.odsStatic -et.ods


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Static met.ods


pri"ate static int student%ount$public staticint )etStudent%ount({

return student%ount$}

}

where, public means that the method can be called from ob/ects of

other classes

staticmeans that the method is static and should be called btping,'Class8ame$'method8ame$ ;or e!ample, in this case,we call the method StudentRecordgetStudent!ount"#

int is the return tpe of the method$ This means that the methodshould return a value of tpe int

get+tudentCount the name of the method

() this means that our method does not have an parameters


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Coding uidelines for -et.ods

6ethod names should start with a small letter$

6ethod names should sound like a verb

3rovide documentation before the declaration of the

method$ 1ou can use *avadocs stle for this$


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0.en to Define Static -et.od1

=hen the logic and state does not involve ob/ectinstances (different propert values of different ob/ectinstances do not pla a role in the logic)

Computation method

add(int !, int ) method

=hen the logic is a convenience without creating anob/ect instance

int mint @ 4nteger$parse4nt(>)E


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Source Code for StudentRecordclass


// ,nstance "ariables

pri"ate Strin) name$

pri"ate Strin) address$

pri"ate int a)e$

pri"ate double math2rade$

pri"ate double en)lish2rade$

pri"ate double science2rade$

pri"ate double a"era)e$

pri"ate static int student%ount$


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Source Code for StudentRecordClass

/**

* Returns the name of the student ccessor method(

*/

public Strin) )etame({

return name$

}

/**

* %han)es the name of the student :utator method(*/

public "oid setame Strin) temp ({

name temp$

}


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Source Code for StudentRecord Class

/**

* %omputes the a"era)e of the en)lish; math and science

* )rades ccessor method(

*/

public double )et"era)e({

double result 1$

result math2rade3en)lish2rade3science2rade (/4$

return result$

}

/**

* returns the number of instances of StudentRecords

* ccessor method(

*/

public static int )etStudent%ount({

return student%ount$

}


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Sample Source Code t.at usesStudentRecord Class

public class StudentRecord$%ample{

public static void main" String& args #{

//create three ob(ects )or Student recordStudentRecord annaRecord = new StudentRecord"#;StudentRecord beahRecord = new StudentRecord"#;StudentRecord crisRecord = new StudentRecord"#;

//set the name o) the studentsannaRecordset*ame"+,nna+#;beahRecordset*ame"+-eah+#;crisRecordset*ame"+!ris+#;

//print anna's name

S.stemoutprintln" annaRecordget*ame"# #;

//print number o) studentsS.stemoutprintln"+!ount=+StudentRecordgetStudent!ount"##;}

}

static method

instance method


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*rogram Output

nna

Student %ount 1


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Demo:Demo:

Exercise /: Static2'nstance variables 3Exercise /: Static2'nstance variables 3Static2'nstance met.odsStatic2'nstance met.ods

!"!#$javase$createclass%&ip!"!#$javase$createclass%&ip


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OverloadingOverloading-et.ods-et.ods


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-et.od Overloading

6ethod overloading

allows a method with the same name but differentparameters, to have different implementations and returnvalues of different tpes

can be used when the same operation has differentimplementations$

Alwas remember that overloaded methods have thefollowing properties:

the same method name

different number of parameters or different tpes ofparameters

return tpes can be different or the same


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Example

public static void main" String&' args #{

StudentRecord annaRecord = new StudentRecord"#;

annaRecordset*ame"+,nna+#;annaRecordset,ddress"+1hilippines+#;

annaRecordset,ge"23#;annaRecordset0athGrade"45#;

annaRecordset$nglishGrade"633#;annaRecordsetScienceGrade"255#;

//overloaded methodsannaRecordprint" annaRecordget*ame"# #;annaRecordprint" annaRecordget$nglishGrade"#7

annaRecordget0athGrade"#7 annaRecordgetScienceGrade"##;

}


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Output

we will have the output for the first call to print,

ame.nna

ddress.hilippines

)e.8=

we will have the output for the second call to print,

ame.nna

:ath 2rade.1?1

@n)lish 2rade.A=?=

Science 2rade.811?1


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ConstructorsConstructors

)Constructor)Constructor-et.ods+-et.ods+


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Constructors

Constructors are important in instantiating an ob/ect$ 4tis a method where all the initialiFations are placed$

The following are the properties of a constructor:

Constructors have the same name as the class

A constructor is /ust like an ordinar method with some differences

Constructors does not have an return value

1ou cannot call a constructor directl, it gets called indirectl when

ob/ect gets instantiated


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Constructors

To declare a constructor, we write,

*( {

*

}


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Default Constructor )-et.od+

The default constructor )no5arg constructor+

is the constructor without an parameters$

4f the class does not specif an constructors, then andefault constructor gets created automaticall b thecompiler

4f there is alread a constructor, then default constructordoes not get created automaticall b the compiler

E l D f lt C t t


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Example: Default Constructor-et.od of StudentRecord Class// Default constructor of StudentRecord class

public StudentRecord({

//some code here

}


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Overloading Constructor -et.odspublic StudentRecord({

//some initiali7ation code here

}

public StudentRecordStrin) temp({

this?name temp$

}

public StudentRecordStrin) name; Strin) address({

this?name name$

this?address address$

}

public StudentRecorddouble m2rade; double e2rade;double s2rade({

math2rade m2rade$

en)lish2rade e2rade$

science2rade s2rade$

}


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Example: 6sing Constructors

public static "oid main Strin)[# ar)s ({

//create three obBects for Student record

StudentRecord annaRecord

new StudentRecord6nna6($

StudentRecord beahRecord

new StudentRecord6Ceah6;

6hilippines6($

StudentRecord crisRecord

new StudentRecord1;A1;811($

//some code here

}


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7t.is)+8 constructor call

Constructor calls can be chained, meaning, ou cancall another constructor from inside anotherconstructor$

=e use the this()call for this

There are a few things to remember when using thethis()constructor call:

=hen using the this constructor call, 4T 6U+T


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Example

2: public StudentRecord"#{8: this"+some string+#;9:: }3:: public StudentRecord"String temp#{


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Demo:Demo:

Exercise #: ConstructorExercise #: Constructor!"!#$javase$createclass%&ip!"!#$javase$createclass%&ip


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77t.is8 Referencet.is8 Reference


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7t.is8 reference

The thisreference

refers to current ob/ect instance itself

used to access the instance variables

To use the this reference, we tpe,

this?

1ou can onl use the this reference for instance variablesand 8


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7t.is8 reference

The thisreference is assumed when ou call a methodfrom the same ob/ect

public class 6Class ?

void a6ethod() ?

BB same thing as this$another6ethod()

another6ethod()E

H

void another6ethod() ?

BB method definition here$$$

H

H


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Example

public "oid set)e int a)e ({

this?a)e a)e$

}


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Demo:Demo:

Exercise 9: 7t.is8Exercise 9: 7t.is8!"!#$javase$createclass%&ip!"!#$javase$createclass%&ip


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,ccess -odifiers,ccess -odifiers

, - difi


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,ccess -odifiers

There are four different tpes of member accessmodifiers in *ava:

public (5east restrictive)

protected

default

private (6ost restrictive)

The three access modifiers in blue color are e!plicitl

written in the code to indicate the access tpe, for theIrd one (>default), no keword is used$

bli ibilit


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public accessibility

publicaccess

specifies that class members (variables or methods) areaccessible to anone, both inside and outside the classand outside of the package to which the class belongs

An ob/ect that interacts with the class can have accessto the public members of the class$

Jeword: public

E l 7 bli 8 , - dif


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Example: 7public8 ,ccess -odifer


// public access to instance "ariable

publicint name$

// public access to method

publicStrin) )etame({

return name$

}

}

t t d ibilit


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protected accessibility

protectedaccess

+pecifies that the class members are accessible onl tomethods in that class and the subclasses of the class$

The subclass can be in different packages

Jeword: protected

E l 7 t t d8 , - difi


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Example: 7protected8 ,ccess -odifier


//protected access to instance "ariable

protectedStrin) name$

//protected access to method

protectedStrin) )etame({

return name$

}

}

default accessibility


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default accessibility

Default access

specifies that onl classes in the same package can haveaccess to the class. variables and methods

no actual keword for the default modifierE it is applied in

the absence of an access modifier$


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private accessibility


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private accessibility

privateaccessibilit

specifies that the class members are onl accessiblewithin the class

Jeword: private

Example: 7private8 ,ccess -odifier


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Example: private ,ccess -odifier


//pri"ate access to instance "ariable

pri"ateint name$

//pri"ate access to method

pri"ateStrin) )etame({

return name$

}

}

ava *rogram Structure:;. , - difi


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;.e ,ccess -odifiers

Coding uidelines


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Coding uidelines

The instance variables of a class should normall bedeclared private, and the class will /ust provideaccessor and mutator methods to these variables$


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Demo:Demo:

Exercise


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Summary

Defining our own classes Declaring ;ields (instance, staticBclass)

Declaring 6ethods (accessor, mutator, static)

eturning values and 6ultiple return statements

The this reference

6ethod overloading

Constructors (default, overloading, this() call)

3ackages Access 6odifiers (default, public, private, protected)


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;.an= you>;.an= you>

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clase 02- programacion orientada a objetos java ii

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