Download Lab 13 Name - Villanova Computer Science

Lab13Name:________________________Checked:______
Objectives:
InthislabwewilllearnhowtoaccesstextfilesusingScannertogettheircontents.We
willalsouseScannerinothernovelways,includingreadingdatadirectlyfromawebpage!
Beforeyoubegin,createafolderforyourLab13files.Itisimportanttosaveallthedata
andprogramfilesforthislabinthesamefolder.
PartI:
Preparation:
Submit4files:YouVeGotMoreShoes.java,ShoeCollection.java,Shoe.java(Lab12,
partB)andLab13a.java(seebelow)throughBlackboardby8:00amthemorningofLab.
a.Readingvaluesfromafileandstoringtheminanarray
Inpart(d)ofLab11weexploredhowtoinputvaluesfromtheuserandstoretheminan
array.ReviewyourprogramLab11d.java–recallthatitusesScannertoinputinteger
valuesfromtheuser.SaveacopyofthisprograminyourLab13folder,renamingitas
Lab13a.java
Supposeyouhavealonglistofvaluesstoredinafile,andyouwanttostoretheminan
arrayof100elements.Forexample,thefile:
www.csc.villanova.edu/~map/1051/s16/examples/oneHundredInts.txtYouwouldnot
wanttotypethenumbersinordertoentertheminyourprograminteractively!
• DownloadthisfileandsaveinyourLab13folder.OpenitinjGrasptoinspectit.
• Makesurethefilewasnotcorruptedduringdownload(thishappenssometimes)–it
shouldcontain100numbersandnothingelse–checkbeforeproceeding.
• InJava,youcandirecttheScannertoinputfromafile,insteadoffromthekeyboard.
Dothisasfollows:
o IntheinstantiationoftheScannerobject,replaceSystem.inbythefilefrom
whichyouare“reading”,i.e.:
Scanner scan = new Scanner(new File("oneHundredInts.txt"));
Importclassesfromjava.io:
import java.io.*;
o Add“throws IOException”totheheadingofyourmainmethod:
o
public static void main(String[] args) throws IOException
•
Sinceyouwanttoinput100numbers,youneedtoenlargethearraytohold100
integers.
Troubleshooting:Remembertodouble-checkthatthefileoneHundredInts.txtissaved
inthesamefolderasyourprogramandcontainsthecorrectdata(alistof100numbers).
VillanovaUniversityCSC1051www.csc.villanova.edu/~map/1051Dr.Papalaskari
PartII:
b.Processingatextfile,linebyline
www.csc.villanova.edu/~map/1051/s16/examples/FileInput.java
//***************************************************************
// FileInput.java
Author: MAP
// Demonstrates the use of Scanner to read text file input.
//***************************************************************
import java.util.Scanner;
import java.io.*;
public class FileInput
{
//-----------------------------------------------------------// Reads text from a file and prints it in uppercase.
//-----------------------------------------------------------public static void main (String[] args) throws IOException
{
String line;
Scanner fileScan;
File myFile = new File("sample.txt");
fileScan = new Scanner (myFile);
// Read and process each line of the file
while (fileScan.hasNext())
{
line = fileScan.nextLine();
System.out.println (line.toUpperCase());
}
}
}
1) Download and compile this program; create a small text file named sample.txt and
save it in the same folder as the program (you can create the file directly in JGrasp – under
File-> New, choose “Plain text” instead of “Java” for the file type). Run FileInput – what
does it do?
____________________________________________________________________
____________________________________________________________________
2) Modify it to use the parameter args[0] of main() as the file name. Do this as follows:
• Replace the use of
File myFile = new File("sample.txt");
with
File myFile = new File(args[0]);
•
•
In jGrasp, select “Run Arguments” from the Build menu, and provide the file name as
an argument (parameter) to main by typing sample.txt in the box that appears
above your program. In this way, you can run your program with different files,
without modifying the code. Try it with the dataset file for next project:
www.csc.villanova.edu/~map/1051/s16/examples/titanic.txt VillanovaUniversityCSC1051www.csc.villanova.edu/~map/1051Dr.Papalaskari
c.ScanningfromaString
JustaswecanuseaScannertoinputfromafileorfromSystem.in,wecanalsousea
Scannerto“input”fromaString!
1)Trythiscode:Lab13c.java
//********************************************************************
// Lab13c.java
MA Papalaskari
// Simple example: scanning from a String
//********************************************************************
import java.util.Scanner;
public class Lab13c
{
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
System.out.print("Please type 3 words:
String line = scan.nextLine();
");
Scanner scanLine = new Scanner(line);
String word1 = scanLine.next();
String word2 = scanLine.next();
String word3 = scanLine.next();
System.out.println("Word 1: " + word1);
System.out.println("Word 2: " + word2);
System.out.println("Word 3: " + word3);
scanningfrom
aString
}
}
Run :Lab13c.java– what does it do?
____________________________________________________________________
____________________________________________________________________
d.ScanningfromaStringanddoingsomethinguseful
Next,wewillcreateLab13d.javabymodifyingLab13c.javasothatitdoessomething
moreinterestingwiththeinput.Ournewprogramwilltreattheinputasacommandfor
asimplenumericcomputation.
Forexample,theinputmightbe:
55 * 83
Wewanttheprogramtocomputeandprinttheproduct4565.First,runLab13c.java
withthisinputandobservehowitpicksoutthe“55”,“*”,“83”asword1,word2,and
word3,respectively.NotethatthecodeusesscanLine.next()whichproducesString
tokensandthatwasfinebecauseword1,word2,andword3areStrings.Butnowyouwant
tousethevalues55and83asnumbers,sothevariableshavetobeoftypedouble(we
VillanovaUniversityCSC1051www.csc.villanova.edu/~map/1051Dr.Papalaskari
coulduseint,butdoublewillallowyoutohandleawiderrangeofvalues),andyou
needtoobtaintheirvaluesusingscanLine.nextDouble()insteadofscanLine.next().
Canyouusetheseideastocreateasimplecalculator?Changethepromptfrom“Please
enter3words”to“Calculate:”
Notethatyoucantestthevalueofword2.charAt(0)toseeifitisequalto‘+’,‘*’,etc,and,
accordingly,computetheresult.(Ifyouwanttobeabletohandlemorethan2operators,
itisbesttouseaswitchstatement.)
Sampleruns:
----jGRASP exec: java Lab13d
Calculate:
9.3 + 44.7
= 54.0
----jGRASP exec: java Lab13d
Calculate:
55 * 83
= 4565.0
e.Inputdataintoanarray
ThetechniquedescribedinPartsCisalsousefulforprocessingdataorganizedin
columnsandinputtingthatintoanarray.GobacktothecodeforPartC(NOTPartD)and
modifythecodesothatitinputs8wordsintoanarrayof8Strings.(Besuretoreplace
thevariablesword1,word2etcbyanarrayword[0],word[1],etc.anduseafor-loopto
gettheinput.Thewordsshouldthenbeprintedbackwards.
Tabdelimiteddata:
Sometimestheinputtokenscancontainspaces.Forexample,the“words”couldbe
countrynames:
India United States France China Germany Greece South Korea Brazil
Thesearestilljust8countries!Insuchsituations,atabcanbeusedasadelimiter,sothe
Stringwouldbestoredas:
"India\tUnited States\tFrance\tChina\tGermany\tGreece\tSouth Korea\tBrazil"
InorderforyourScannertouseadelimiterotherthanwhitespace,youneedtospecify
thisbeforedoinganyinput:
scanLine.useDelimiter("\t");
Samplerun:
----jGRASP exec: java Lab13d
Enter 8 country names, all in one line, separated by tabs:
India
France
Japan
India
Greece
United States
South Korea
Mali
South Korea
United States
Greece
India
Note:thesearetabcharacters
Japan
France
India
Mali
VillanovaUniversityCSC1051www.csc.villanova.edu/~map/1051Dr.Papalaskari
f.Processingdatafromtextfiles,organizedincolumns(CombinePartsb&e)
The technique described in (e) is useful for processing text files containing data
organizedincolumns.Wenowmodify FileInput.java from(b),above,sothatafterit
inputseachline,itusesthetechniqueof Lab13e.java,above(i.e.,asecondScanner)to
“scan”8wordsfromeachlineinthefileandstorethesewordsinanarray,thenprintthe
contentsofthearraybackwards.Trythiswiththefollowingfile:
http://www.csc.villanova.edu/~map/1051/s16/examples/eightwords.txt
Sampleoutput:
Line: India
France
Mali
South Korea
United States
Greece
United Arab Emirates
Japan
France
India
Line:
apple
orange
pineapple
raspbery
grape
persimmon
fig
asian pear
orange
apple
Line: black
green
blue
red
dark gray
light gray
gray
white
black
Japan
asian pear
white
gray
United Arab Emirates
fig
Greece
persimmon
light gray
United States
grape
dark gray
raspbery
red
blue
South Korea Mali
pineapple
green
g.(Optional)Inputdirectlyfromawebsite
Wouldyoulikeyourprogramtoaccessawebsitedirectly?Hereishow.Youneedto
1)Addanotherimportdirectiveatthebeginningoryourprogram:
import java.net.URL;
2)SetupyourScannertoreadfromtheurlinsteadofafile.Hereisanexample:
String myurl =
"http://www.csc.villanova.edu/~map/1051/s16/examples/oneHundredInts.txt";
InputStream inStream = new URL(myurl).openStream();
Scanner webScan = new Scanner (inStream);
3)Nowyoucanuse webScan asanyotherScanner object,toinputfromawebpage
asifitwereanyothertextfile.Tryitwithyourprogramlab13a.java.
Thistechniquewillworkwithmostwebpages,aslongastheycanbereadastext
(includinghtmlfiles).
VillanovaUniversityCSC1051www.csc.villanova.edu/~map/1051Dr.Papalaskari
Lab13Comments
Name:________________________
Commentsonthislab,please:
Whatwasthemostvaluablethingyoulearnedinthislab?
Whatdidyoulikebestaboutthislab?
Wasthereanyparticularproblem?
Doyouhaveanysuggestionsforimprovingthislabasaneffectivelearningexperience?
VillanovaUniversityCSC1051www.csc.villanova.edu/~map/1051Dr.Papalaskari