Java input output operation related introduction.

Java input output

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I/O Operations

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Agenda
Console Operations
File Operations2

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Objectives
At the end of this module, you will be able to:
Understand Console operations
Understand File operations

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Reading & Printing to Console

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•ThepreferredmethodofreadingconsoleinputinJava2istouseacharacterstream
•InputStreamReaderclassactsasabridgebetweenbyteandcharacterstreams
•ConsoleinputisaccomplishedbyreadingfromSystem.in
•Togetacharacter-basedstream,youwrapSystem.ininaBufferedReaderobject
Reading Console Input -Stream Wrapping

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Reading Console Input -Stream Wrapping
TheBufferedReaderclasssupportsabufferedinputstream.Itsmostcommonlyused
constructorisshownasfollows:
BufferedReader(ReaderinputReader)
HereinputReaderisthestreamthatislinkedtotheinstanceofBufferedReaderthatis
beingcreated.Readerisanabstractclass.Oneofitsconcretesubclassesis
InputStreamReader,whichconvertsbytestocharacters.Toobtainan
InputStreamReaderobjectthatislinkedtoSystem.in,usethefollowingconstructor:
InputStreamReader(InputStreaminputStream)

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Reading Console Input -Stream Wrapping
BecauseSystem.inreferstoanobjectoftypeInputStream,itcanbeusedforinputStream.
Puttingitalltogether,thefollowinglineofcodecreatesaBufferedReaderthatisconnected
tothekeyboard,andwhichinturnenablescharacterinputfromabytestreamInputStream
thatisSystem.in).
BufferedReaderbr=newBufferedReader(newInputStreamReader(System.in));

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package m10.io;
import java.io.*;
public class BRRead{
public static void main (String args[ ]) throws IOException {
char c;
BufferedReader br = new BufferedReader(new
InputStreamReader(System.in));
System.out.println(“Enter Characters, ‘q’ to quit”);
do {
c = (char) br.read( );
System.out.println( c );
}while (c != ‘q’);
}
}
Reading Characters
Refer documentation for
BufferedReader and
InputStreamReader

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Reading Characters
intread()throwsIOException
Whenevertheread()methodiscalled,itreadsacharacterfromtheinputstreamand
returnsanintegervalue.Iftheendofthestreamisencountered,-1isreturned.

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packagem10.io;
importjava.io.*;
publicclassBRReadLine{
publicstaticvoidmain(Stringargs[])throwsIOException{
Stringstr;
BufferedReaderbr=newBufferedReader(new
InputStreamReader(System.in));
System.out.println(“Enter Characters,‘stop’toquit”);
do{
str=br.readLine();
System.out.println (str);
}while(!str.equals(“stop”));
}
}
The above program reads and displays lines of text until you enter the word “stop”.
ReadingStrings

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•print()andprintln()areconsoleoutputmethodsdefinedinPrintStreamclass
•System.outisabytestreamusedtowritebytes
Writing Console Output

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Writing & Reading From File

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Reading&WritingtoFileusingFileReader&FileWriter
TheFileclassisaconvenienceclassforwritingcharacterfiles.TheFileclassdealsdirectly
withfilesandthefilesystem.TheFileclassdoesnotspecifyhowinformationisretrieved
from,orstoredinfiles,itdescribesthepropertiesofafileitself.AFileobjectisusedtoobtain
ormanipulateinformationassociatedwithadiskfile,suchasthepermissions,time,dateand
directorypath.
publicintread()throwsIOException(Readasinglecharacter)
publicintread(char[]cbuf,intoff,intlen)throwsIOException
publicvoidwrite(intc)throwsIOException(Writeasinglecharacter)

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packagem10.io;
importjava.io.*;
publicclassCopy{
publicstaticvoidmain(String[]args)throwsIOException{
FileinputFile=newFile(”Source.txt");
FileoutputFile=newFile(”Target.txt");
FileReaderin=newFileReader(inputFile);
FileWriterout=newFileWriter(outputFile);
intc;
while((c=in.read())!=-1)
out.write(c);
in.close();
out.close();
}
}
Reading&WritingtoFileusingFileReader&FileWriter
Refer documentation for
FileReader and FileWriter

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importjava.io.*;
classCopyFile{
publicstaticvoidmain(Stringargs[])throwsIOException{
inti;
FileInputStream fin;
FileOutputStream fout;
try{
fin=newFileInputStream(args[0]);
}
catch(FileNotFoundException e){
System.out.println("File NotFound");
return;
}
Copyimage
Why can’t we use FileReader and FileWriter here?

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Copyimage(Contd.).
try{
fout=newFileOutputStream(args[1]);
}
catch(IOExceptione){
System.out.println("Error OpeningOutputFile");
return;
}
try{
do{
i=fin.read();
if(i!=-1)
fout.write(i);
}while(i!=-1);
}
catch(IOExceptione){
System.out.println("File Error");
}
fin.close();
fout.close();
}
}

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Copyimage(Contd.).
Torunthisprogram
C:\javaCopyFilesource.bmpdest.bmp
Itwillcopyimagefromsource.bmptodest.bmp

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