unit5 - packages

7/23/2019 Unit5 - Packages

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Basic Java

Unit 5 - Packages



Basic Javaop!right " #$$% Pratian Technologies

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Unit 5 & Packages

Topics

'aming lashes

Packagesreating Packages in Java

ccessing Package em*ers

ccess +peci,iers

'ested Packages

The import statement




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Unit 5 & Packages

class onnection

/

p0*lic void connectTo1racle()

/

22 Logic o, connecting to

1racle 3B

4

4

onnect to

1racle

developed

*! team

'aming lashes

class onnection

/

p0*lic void connectTo+!*ase()

/

22 Logic o, connecting to

+!*ase 3B

4

4

class 3ata*ase6riter

/

p0*lic static void main(+tring7 8 s)

/

onnection connection 9 newonnection():

connection.

connectTo1racle():

4

4

nother Team ; 0ses 0tilit! classes

provided *! *oth teams < =

//Error

onnect to

+!*ase

developed

*! team =

6hat happens when

all the three classes

are integrated <

3ata*ase6riter

is e>ec0ted ?

@ow do we solve

the pro*lem o,

'ame clashes ?




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Unit 5 & Packages

Packages

Package is a collection o, related classes and inter,aces.

Packages are 0sed to avoid naming con,licts.

The! also provide access protection.




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Unit 5 & Packages

reating Packages

hoose an appropriate

name ,or the package.

Use the package

statement at the top o,

every source file that

contains the classes or

inter,aces.

package oracleDB;

class onnection

/


/ 4

AAAA.

4

package cybaseDB;

class onnection

/


/ 4

AAAAA..

4




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Unit 5 & Packages

reating Packages



Use the package




inter,aces.

package oracleDB

class onnection

/


/ 4

AAAA.

4

package cybaseDB:

class onnection

/


/ 4

AAAAA..

4

Note

package statement m0st *e the

,irst line in the so0rce ,ile


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Unit 5 & Packages

reating Packages



Use the package




inter,aces.

package oracleDB

class onnection

/


/ 4

AAAA.

4

package cybaseDB:

class onnection

/


/ 4

AAAAA..

4

Note

There can *e onl! one packagestatement in each so0rce ,ile andit applies to all t!pes in the ,ile.



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Unit 5 & Packages

Package is a li*rar! as well

ph!sical ,older with the same name as the package has

to created

ll the .class ,iles *elonging to that package has to *e

incl0ded in that ,older.

oracle3B.onnection s!*ase3B.onnection



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Unit 5 & Packages

lasspath +etting lasspath setting is 0sed *! the JC to locate class ,iles

lass loader looks ,or a class ,ile in the path mentioned and loads the

*!tecodes in memor! The environment varia*le lasspath needs to *e set to the parent

,older o, the package ,older



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Unit 5 & Packages

ccessing package mem*ers

De,erring to the mem*er *! its ,0ll! E0ali,ied name

class or inter,ace *elonging a package needs to *e re,erred toas package name.class name

class 3ata*ase6riter

/

p0*lic static void main(+tring7 8 s)

/

oracleDB.Connection conn 9 new

oracleDB.Connection():

conn. connectTo1racle():

4

4



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Unit 5 & Packages

reating Packages

+0mmariFing steps involved in creating packages

i. Incl0de package statement

ii. reate the corresponding ph!sical ,older str0ct0re

iii. +et the classpath environment varia*le



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Unit 5 & Packages

ccess +peci,iers - Devisited p0*lic

n! class mem*er declared as p0*lic is visi*le (or accessi*le) to

an! class *elonging to an! package

protected n! class mem*er declared as protected is visi*le (or accessi*le)

to all classes in the same package as well as to s0* classes*elonging to other packages

de,a0lt n! class mem*er declared witho0t an! o, the a*ove is visi*le (or

accessi*le) to all classes in the same package onl!.

private n! class mem*er declared as private is visi*le (or accessi*le)

onl! within the same class



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Unit 5 & Packages

Gnowledge heck Incl0de an! class that !o0 have written in a package and 0se the

class in another class.

'ote H To r0n a class that *elongs to a package remem*er to provide

the ,0ll! E0ali,ied class name as arg0ment to the ava command



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Unit 5 & Packages

Package 'aming onvention It is important to ens0re 0niE0eness o, package names

+ince the Internet domain names are 0niE0e ,or acompan! the reversed domain name is 0sed to name apackage. K> com.pratian.avatraining ,or a package avatraining

Package names are written in lowercase to avoid con,lictwith the names o, classes or inter,aces.

Packages in the Java lang0age itsel, *egin with java. or javax.



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Unit 5 & Packages

'ested Packages - K>ample

lass 0stomer *elongs topackage

com.pratian.pb.model

In another class 0stomer31it needs to

*e accessed as

com.pratian.pb.model.Customer

o0ld *e

0m*ersome



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Unit 5 & Packages

The import shorthand

The import statement is a convenience s!nta> 0sed to

access classes that *elong to a package


makes it easier to

access package

mem*ers


m0st appear at the

*eginning onl! ne>t to

the package statement




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Unit 5 & Packages

The import shorthand

The wild card character * is 0sed to speci,!

all classes o, the

package

U it 5 P k




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Unit 5 & Packages

'ested Packages package can *e nested inside another package.

. separated name is 0sed to nest package within packages.

1n compilation o, the a*ove code we wo0ld get a 0itar.class ,ilethis ,ile sho0ld *e incl0ded in a director! instr0ments2western.

H2m!proect2instr0ments2western20itar.class

package instr0ments.western:

p0*lic class 0itar implements

instr0ments.Instr0ment

/

p0*lic void pla!() / 4

4

U it 5 P k




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Unit 5 & Packages

JD Miles The Java rchive (JD) ,ile ,ormat ena*les to *0ndle

m0ltiple ,iles into a single archive ,ile.

'eed ,or JD ,iles Compression & The JD ,ormat allows compression o, ,iles ,or

e,,icient storage.

Decreased download time & I, a li*rar! is *0ndled in a JD ,ilethe reso0rces can *e downloaded in a single transaction witho0tthe need ,or opening a new connection ,or each ,ile.

Portability - The mechanism ,or handling JD ,iles is a standardpart o, the Java plat,ormNs core PI.

U it 5 P k




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Unit 5 & Packages

reating a JD Mile The *asic ,ormat o, the command ,or creating a JD

,ile isH

jar cvf jar-file input-file(s) The options and arg0ments 0sed in this command

The c option indicates that !o0 want to create a JD ,ile.

The f option indicates that !o0 want the o0tp0t to go to a file rather than to stdo0t.

jarfile is the name that !o0 want the res0lting JD ,ile to have.B! convention JD ,ilenames are given a .ar e>tensiontho0gh this is not reE0ired.

The inputfile!s" arg0ment is a space-separated list o, one ormore ,iles that !o0 want to incl0de in !o0r JD ,ile. The inp0t-,ile(s) arg0ment can contain the wildcard O s!m*ol. I, an! o, the

inp0t-,iles are directories the contents o, those directories areadded to the JD archive rec0rsivel!.

This command will generate a compressed JD ,ileand place it in the c0rrent director!.

Unit 5 Packages




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Unit 5 & Packages

Ciewing contents o, a JD Mile The *asic ,ormat o, the command ,or viewing the contents

o, a JD ,ile isH

jar tvf jar-file The options and arg0ments 0sed in this command areH

The t option indicates that !o0 want to view the table o, contentso, the JD ,ile.

The f option indicates that the JD ,ile whose contents are to *eviewed is speci,ied on the command line.

The jarfile arg0ment is the path and name o, the JD ,ile whosecontents !o0 want to view.

The t and f options can appear in either order *0t there m0st not

*e an! space *etween them. This command will displa! the JD ,ileNs ta*le o, contents

to stdo0t.

Unit 5 Packages




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Unit 5 & Packages

dding a JD ,ile to class path

6hile adding JD ,iles to the classpath it is necessar! to

add not 0st the location *0t also the ,ile name o, the

JD ,ile.

K.g. & onsider a JD ,ile called !Li*.ar located in

HQ!JavaQProectQ!Li*.ar

set classpath9HQ!JavaQProectQ!Li*.ar

nd not

set classpath9HQ!JavaQProectQ

Unit 5 Packages




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Unit 5 & Packages

Please try to limit the questions to the topics discussed during the session. Thank you.

R0estion time

Unit 5 & Packages




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Unit 5 & Packages

reating Packages

reating packages involves the ,ollowing three steps

i. #nclude $package%

statement



Unit 5 & Packages




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Unit 5 Packages

reating Packages



ii. Create t&e corresponding

p&ysical folder structure


Unit 5 & Packages



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Unit 5 Packages

reating Packages




iii. 'et t&e $classpat&%

environment variable

unit5 - packages

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