Java io stream operation related introduction.

java io operation

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I/O Streams-
Introduction

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Agenda
Introduction to I/O Streams
Predefined I/O Streams2

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Objectives
At the end of this module, you will be able to:
Understand I/O Streams and its categories
Understand about predefined I/O Streams

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I/OStreams

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•JavaprogramsperformI/Othroughstreams.Astreamis:
–anabstractionthateitherproducesorconsumesinformation
–linkedtoaphysicaldevicebytheJavaI/Osystem
•Allstreamsbehavesimilarly,eveniftheactualphysicaldevicestowhichtheyarelinked
differ.
•ThusthesameI/Oclassescanbeappliedtoanykindof
deviceastheyabstractthedifferencebetweendifferentI/Odevices.
I/OStreams

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•Java’sstreamclassesaredefinedinthejava.iopackage.
•Java2definestwotypesofstreams:
–bytestreams
–characterstreams
•Bytestreams:
–provideaconvenientmeansforhandlinginputandoutputofbytes
–areusedforreadingorwritingbinarydata
•Characterstreams:
–provideaconvenientmeansforhandlinginputandoutputofcharacters
–useUnicode,and,therefore,canbeinternationalized
I/OStreams(Contd.).

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•Systemclassofthejava.langpackagecontainsthreepredefinedstreamvariables,in,out
anderr.
•ThesevariablesaredeclaredaspublicandstaticwithinSystem:
–System.outreferstothestandardoutputstreamwhichistheconsole.
–System.inreferstostandardinput,whichisthekeyboardbydefault.
–System.errreferstothestandarderrorstream,whichalsoistheconsolebydefault.
ThePredefinedStreams

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•System.outsendstheoutputtothestandardoutput stream,whichisconsolebydefault.
•System.err sends the output to the standard error stream, which also happens to be
console by default
•Thereasonbehindhavingtwoseparatestreamsforoutputanderroristhatthestandardo
utputshould beusedforregularprogramoutputswhilestandard
errorshouldbeusedforerrormessages.
DifferencebetweenSystem.outandSystem.err

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•Boththesestreamscanberedirectedtodifferent destinations.
•Wecanredirecttheprogramoutputto a particularlogfileandtheerrormessagestoanother
logfilebyusingthefollowingsyntax:
javaStreamDemo>output.log2>error.log
(whereStreamDemoisthenameoftheclass)
Duringexecution,theprogramoutputwill be stored in output.log while the error message(if
any) will be stored in error.log
System.outandSystem.err(Contd.).

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DemonstrationofSystem.outandSystem.err
classStreamDemo{
publicstaticvoidmain(String[]args){
try{
System.out.print("Writingprogramoutputtotheoutputfile");
inti=0;
intz=100/i;
}
catch(Exception e){
System.err.print("ArithmeticException hasoccured");
}
}
}

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•SystemPropertiesprovideinformationaboutlocalsystemconfiguration.
•WhentheJavaVirtualMachinestarts,itinsertslocalSystemPropertiesintoaSystem
propertieslist.
•We can use methods definedin System classto
accessorchangethevaluesoftheseproperties.
publicstaticPropertiesgetProperties()
publicstaticStringgetProperty(Stringkey)
publicstaticvoidsetProperties(Propertiesprp)
SystemProperties

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SomeoftheImportantPropertiesarelistedbelow:
SystemProperties(contd.).
Key DescriptionofAssociatedValue
java.version JavaRuntimeEnvironmentversion
java.home Javainstallationdirectory
java.class.pathJavaclasspath
os.name Operatingsystemname
user.name User'saccountname
user.home User'shomedirectory
user.dir User'scurrentworkingdirectory

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publicstaticPropertiesgetProperties()
TheSystem.getProperties()methodreturnsan objectofthetypeProperties.
YoucanusethismethodtolistalltheSystem Properties.
System.getProperties()

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DemoofSystem.getProperties()method
importjava.util.*;
classGetPropertiesDemo {
publicstaticvoidmain(String[]args){
Propertiesx=System.getProperties();
x.list(System.out);
}
}

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publicstaticStringgetProperty(Stringkey)
YoucanalsouseSystem.getProperty(StringKey)methodtogetthevalueofaparticular
propertyrepresentedwithakey.
System.getProperty(StringKey)

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classGetPropertyDemo {
publicstaticvoidmain(String[]args){
Stringuser_home=System.getProperty("user.home");
Stringjava_version=System.getProperty("java.version");
Stringjava_home=System.getProperty("java.home");
Stringclass_path=System.getProperty("java.class.path");
Stringos_name=System.getProperty("os.name");
Stringuser_name=System.getProperty("user.name");
Stringuser_dir=System.getProperty("user.dir");
System.out.println("Theuserhomedirectoryis"+user_home);
System.out.println("Thejavaversionis"+java_version);
System.out.println("TheJavaHomedirectoryis"+java_home);
System.out.println("Theclasspathissetto"+class_path);
System.out.println("TheOperatingSystemis"+os_name);
System.out.println("Theusernameis"+user_name);
System.out.println("Theworkingdirectoryis"+user_dir);
}
}
System.getProperty(StringKey)-Demo

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System.getProperty(StringKey)-Demo
Output:
TheuserhomedirectoryisC:\Users\harb
Thejavaversionis1.6.0_05
TheJavaHomedirectoryisD:\ProgramFiles\java1.6\jdk1.6.0_05\jre
Theclasspathissetto.;E:\app\harb\product\11.1.0\db_1\oui\jlib\classes12.jar;E:\Training\PR
P2012JAVA\ExceltoJava\jxl-2.6.9.jar;
TheOperatingSystemisWindowsVista
Theusernameisharb
TheworkingdirectoryisD:\Java\day10\io

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publicstaticvoidsetProperties(Propertiesprp)
TheSystem.setProperties(Propertiesprp)methodsetsthesystempropertiestotheProperti
es argument.
Youcanusethismethodtochangethesystem propertiesasperyourrequirement.
System.setProperties()

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importjava.util.*;
publicclassSystemPropertiesDemo {
publicstaticvoidmain(String[]args){
System.out.print("Previous valueofJavaHome:");
System.out.println(System.getProperty("java.home"));
Propertiesp=System.getProperties();
p.put("java.home", "D:\\ProgramFiles\\java1.5\\jdk1.5.0_02");
System.setProperties(p);
System.out.print("New valueofJavaHome:");
System.out.println(System.getProperty("java.home"));
}
}
System.setProperties()-Demo
Theabovecodewhenexecuted,prints:
PreviousvalueofJavaHome:D:\ProgramFiles\java1.6\jdk1.6.0_05\jre
NewvalueofJavaHome:D:\ProgramFiles\java1.5\jdk1.5.0_02

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ByteStreams
InputStream OutputStream
I/OStreamshierarchy
FileInputStre
am
ObjectInputStrea
m
BufferedInputStre
am
ManyMoreInputStreamclas
ses
ManyMoreOutputStreamclas
ses
FileOutputStrea
m
BufferedOutputStrea
m
ObjectOutputStre
am
Abstract
c lass
Abstract
class

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CharacterStreams
Reader Writer
I/OStreamshierarchy(Contd.).
FileRead
er
InputStreamRea
der
BufferedRea
der
ManyMoreReaderclasses ManyMoreWriterclasses
FileWriter
BufferedWrit
er
OutputStreamWrit
er
Abstrac
tclass
Abstract
class

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Toread&writedataintobuffer
ByteStreamclasses
Toread&writedataintofile
Toread&writeobjectinto
secondarydevice(serialization
)
FileInputStream
FIleOutputStream
BufferedInputStream
BufferedOutputStrea
m
ObjectInputStream
ObjectOutputStrea
m

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To read & write data into buffer
Character Stream classes
To read & write data into file
Bridge from character stream
to byte stream
FileReader
FIleWriter
BufferedReader
BufferedWriter
InputStreamReade
r
OutputStreamWrit
er

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•MatchthestreamswiththeappropriatephrasesincolumnB
ColumnA ColumnB
1.FileWriter Bytestreamforreadingfromfile
2.FileInputStream Characterstreamforreadingfromfile
3.FileOutputStream Characterstreamforwritingtoafile
4.FileReader Bytestreamforwritingtoafile
Matchthefollowing

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1.Java input output classes are available in ___________package
a.java.lang
b.java.io
c.java.util
2.What are the inbuilt streams available in java.io package
a.System.in
b.System.out
c.System.err
d.All of the above
3.Can data flow through a given stream in both directions?
a.Yes
b.No
Quiz

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Summary
Introduction to I/O Streams
Predefined I/O Streams

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