CS 106A, Lecture 25 Life After CS 106A, Part 1...–Puts a scrollable text areainto it –Provides printand printlncommands to send text outputto that window –contains a mainmethodthat

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CS106A,Lecture25LifeAfterCS106A,Part1

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Plan for today•Announcements•LifeaftertheACMLibraries•LifeafterJava•LifeafterPCprograms–Internetapplications–Mobileapplications

Tomorrow:IntrotoMachineLearning!

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Anonymous Questions•Whatisyourmusictaste?•HowdidyouknowyouwantedtopursueCS?•Whatwasyourfirstcodefor?

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Plan for today•Announcements•LifeaftertheACMLibraries•LifeafterJava•LifeafterPCprograms–Internetapplications–Mobileapplications

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Export to JAR• JAR:JavaArchive.AcompressedbinaryofaJavaprogram.

– ThetypicalwaytodistributeaJavaappasasinglefile.– EssentiallyjustaZIPfilewithJava.classfilesinit.

• MakingaJARofyourprojectinEclipse:– File→Export...→Java→RunnableJARFile

• seehandoutoncoursewebsite

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Life After The ACM Libraries• AllquarterwehavereliedontheACMJavalibraries.

– Karel,ConsoleProgram,RandomGenerator– GraphicsProgram,GOval,GRect,GOval,GLine,GImage,...

• TodaywewillseehowstandardJava programsaremade.

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Using the ACM Librariesimport acm.program.*;

public class MyProgram extends ConsoleProgram {public void run() {

println("Hello, world!");}

}

• ThisisaconsoleprogramwrittenusingtheACMlibraries.– ItusestheConsoleProgram classtorepresentaconsole.– Therunmethodcontainstheprogramcode.– Theprintlnmethodprintsoutputtothegraphicalconsole.

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Pulling Back The CoversMyProgram program = new MyProgram();...program.init();...program.run();...

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Pulling Back The Coverspublic static void main(String[] args) {

MyProgram program = new MyProgram();program.init();program.run();

}

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A Barebones Java Program

public class Hello {public static void main(String[] args) {

System.out.println("Hello, world!");}

}

• Themethodmain isthetrueentrypointforaJavaprogram.– Itmusthavetheexactheadingshownabove.– TheString[] args are"commandlinearguments"(ignored).– Theprintln command'struenameisSystem.out.println.– StandardJavamethodsarestatic unlesspartofaclassofobjects.

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Console Programs• WhatdoestheConsoleProgram libraryclassdo?

– Createsanewgraphicalwindow– Putsascrollabletextarea intoit– Providesprint andprintln commandstosendtextoutput tothatwindow

– containsamainmethod thatcallsyourprogramclass'srunmethod•ConsoleProgram'srun isempty,butyouextendandoverrideit

public class Hello extends ConsoleProgram {public void run() {

println("Hello, world!");}

}

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ACM console inputpublic class Age extends ConsoleProgram {

public void run() {String name = readLine("What's your name? ");int age = readInt("How old are you? ");int years = 65 - age;println(name + " has " + years

+ " years until retirement!");}

}

• TheACMlibraryhassimpleconsoleinputcommandslikereadLine,readInt,readDouble,andsoon.

• Thesemethodsdisplaya'prompt'message,waitforinput,re-promptiftheusertypesabadvalue,andreturntheinput.

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Java console inputpublic class Age {

public static void main(String[] args) {Scanner console = new Scanner(System.in);System.out.print("What's your name? ");String name = console.nextLine();System.out.print("How old are you? ");int age = console.nextInt();int years = 65 - age;System.out.println(name + " has " + years

+ " years until retirement!");}

}

• InstandardJava,youmustcreateaScanner orsimilarobjecttoreadinputfromtheconsole,whichisalsocalledSystem.in.– Itdoesnotautomaticallyre-promptandcancrashonbadinput.

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Graphics ProgramsTheACMlibrarydoesseveralthingstomakegraphicseasier:• Automaticallycreatesanddisplaysawindow onthescreen.

– InstandardJava,wemustdothisourselves;itiscalledaJFrame.

• Setsupadrawingcanvas inthecenterofthewindowInstandardJava,wemustcreateourowndrawingcanvas.

• Providesconvenientmethodstolistenformouseevents.– InstandardJava,eventhandlingtakesabitmorecodetosetup.

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ACM GUI examplepublic class ColorFun extends Program {

public void init() {JButton button1 = new JButton("Red!");JButton button2 = new JButton("Blue!");add(button1, SOUTH);add(button2, SOUTH);addActionListeners();

}public void actionPerformed(ActionEvent event) {

if (event.getActionCommand().equals("Red!")) {setBackground(Color.BLUE);

} else {setBackground(Color.RED);

}}

}

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Java GUI examplepublic class ColorFun implements ActionListener {

public static void main(String[] args) {new ColorFun().init();

}private JFrame frame;public void init() {

frame = new JFrame("ColorFun");frame.setSize(500, 300);JButton button1 = new JButton("Red!");JButton button2 = new JButton("Blue!");button1.addActionListener(this);button2.addActionListener(this);frame.add(button1, "South");frame.add(button2, "South");frame.setVisible(true);

}public void actionPerformed(ActionEvent event) {

if (event.getActionCommand().equals("Red!")) {frame.setBackground(Color.BLUE);

} else {frame.setBackground(Color.RED);

} } }

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Summary• Benefitsoflibraries:

– simplifysyntax/roughedgesoflanguage/API– avoidre-writingthesamecodeoverandover– possibletomakeadvancedprogramsquickly– leverageworkofothers

• Drawbacksoflibraries:– learna"dialect"ofthelanguage("ACMJava"vs."realJava")– lackofunderstandingofhowlowerlevelsorrealAPIswork– somelibrariescanbebuggyorlackdocumentation– limitationsonusage;e.g.ACMlibrarycannotbere-distributedforcommercialpurposes

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Plan for today•Announcements•LifeaftertheACMLibraries•LifeafterJava•LifeafterPCprograms–Internetapplications–Mobileapplications

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Programming Languages

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Programming Languages

https://imgs.xkcd.com/comics/standards.png

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JavaArrayList<Double> evens = new ArrayList<>();for(int i = 0; i < 100; i++) {

if(i % 2 == 0) {evens.add(i);

}}println(evens);

prints [2, 4, 6, 8, 10, 12, … ]

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C++Vector<double> evens;for(int i = 0; i < 100; i++) {

if(i % 2 == 0) {evens.add(i);

}}cout << evens << endl;

prints [2, 4, 6, 8, 10, 12, … ]

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Pythonevens = []for i in range(100):

if i % 2 == 0:evens.append(i)

print evens

prints [2, 4, 6, 8, 10, 12, … ]

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Javascriptvar evens = []for(var i = 0; i < 100; i++) {

if(i % 2 == 0) {evens.push(i)

}}console.log(evens)

prints [2, 4, 6, 8, 10, 12, … ]

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Plan for today•Announcements•LifeaftertheACMLibraries•LifeafterJava•LifeafterPCprograms–Internetapplications–Mobileapplications

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Programs and the Internet

Howdoesyourphone

communicatewithFacebook?

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Programs and the Internet

TheJavaprogramonyourphone talkstotheJavaprogram

atFacebook.

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Facebook

*AndroidphonesrunJava.SodoFacebookservers!

FacebookServer

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FacebookFacebookServer

troccoli@stanford.edu

Is this login ok?

Confirmed. troccoli@stanford.eduis now logged in.

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FacebookFacebookServer

Send me the full name for

troccoli@stanford.edu

“Nick Troccoli”

NickTroccoli

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FacebookFacebookServer

Send me the cover photo for

troccoli@stanford.eduNickTroccoli

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Programs and the Internet

Therearetwotypesofinternet

programs:clientsandservers.

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Programs and the Internet

Clientssendrequests toservers,whorespond tothoserequests.

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Servers Are Computer Programs!

FacebookServer

=

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Servers

Server

RequestsomeRequest

StringserverResponse

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What is a Request?

/* Request has a command */String command;

/* Request has parameters */HashMap<String,String> params;

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Clients

Send

ChatClient

Send

ChatClient> Hello world> Hello world

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Plan for today•Announcements•LifeaftertheACMLibraries•LifeafterJava•LifeafterPCprograms–Internetapplications–Mobileapplications

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Recap•Announcements•LifeaftertheACMLibraries•LifeafterJava•LifeafterPCprograms–Internetapplications–Mobileapplications

Tomorrow:IntrotoMachineLearning!