INFO0062 - Object-Oriented Programminggrailet/docs/INFO0062/2017-2018/... · Compilation and...

INFO0062 - Object-Oriented ProgrammingJava basics and guidelines

Jean-François Grailet

University of Liège

Faculty of Applied Sciences

Academic Year 2017 - 2018

Contact

Jean-François Grailet

Office: 1.14a, Montefiore Institute

Website: http://www.run.montefiore.ulg.ac.be/~grailet/

• Available in both French and English

• Hover1 Teaching menu then select INFO0062 to get the page for this course

• Updated after each session

• Slides, (suggested) solutions and project details

E-mail: [email protected]

1FR: survoler

http://www.run.montefiore.ulg.ac.be/~grailet/

mailto:[email protected]

Java Java and INFO0062 Getting started with Java Network 8 Java SE installation Eclipse, an IDE About Linux Summary

Compilation and execution of a Java program

.java

Compiler Execution

.class

Virtual machine

javac is the compiler which transforms the Java code into bytecode.

Usage (command line):

$ javac Main.java ClassA.java ClassB.java

java is the command used to execute Java bytecode.

Usage (command line):

$ java Main

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Compilation and execution of a Java program (II)

.java

Compiler Execution

.class

Virtual machine

The bytecode is located in .class files, produced by javac.

• For each .java, there will be a .class (Main.java⇒ Main.class)

• Each time you edit a .java, re-compile its .class equivalent for execution.

java requires the class name of the class containing the main() method.

Alternative approach to compile several files with javac:

$ javac *.java

*.java means "all files in the current directory ending in .java".

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Terminology

Java Virtual Machine (JVM): virtual machine able to interpret (and/or compile)bytecode in order to execute it on a specific physical machine.

Java Runtime Environment (JRE): complete environment needed to executeJava programs compiled into bytecode. It is composed of the JVM, some classesimplementing the API (Application Programming Interface) and additional librariesand tools.

Java Development Kit (JDK): environment needed to develop Java programs.It is composed of a special JRE (with additional features for developers), tools(such as a compiler, a debugger, etc.), and other stuff (such as monitoring utilities,documentation, etc.).

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Java and INFO0062


No problem, only solutions

There are several solutions to start practicing Java.

Picking one might depend on your preferred OS (Operating System).

• I.e., whether you are using Windows, macOS (Mac OS X) or a Linux distribution.

Do not wait to pick and test a solution after this session.

• If you do this a few days before the project deadline, you’re going to have a bad time.

• The sooner your start practicing, the better.

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Network 8 as a reference environment

We only ask you one thing: to use Network 8 computers as a reference.

• I.e., your code should compile and run without errors/warnings/crashes.

• This is especially important for the project.

This allows you to ensure your future project will work fine when tested.

• This will also help you to fix warnings that might not appear at your side.

• Or check if you can use a recent Java feature/library.

Network 8 is also your most straightforward solution to code in Java.

• Can be used just like B37 computers (any time), or remotely.

• Note that you need to bring your own mouse to use them directly.

• More details in a few slides.

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Getting started with Java


Main solutions

Using Network 8 computers (reference environment)

• Requires an account on these machines

• (remote usage only) Requires a text editor, a SSH client and a (S)FTP client

(Linux/macOS) Using javac/java directly on your own computer

• Requires installation of Java SE (Standard Edition)

• Requires a text editor

Using an IDE (Integrated Development Environment), like Eclipse

• Requires installation of Java SE (Standard Edition)

• Requires installation of said IDE

How you can use Linux without changing your OS will also be discussed

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Network 8


Network 8

A set of computers located here in Montefiore Institute in two rooms

• Room I.99

• Room "Bibliothèque" (second floor, shortly before I.99)

• Roughly 18 computers (from ms801 to ms818 as of January 2018)

Can be used directly or remotely

Run with a Linux distribution (Ubuntu)

• Therefore, tools and interface are very similar to the B37 computers.

• Those who followed INFO2009 or INFO0946 should be familiar with them.

• Provide Java 8.

To use them, you need to log in with an account.

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Montefiore account

Grants you access and a personal directory on Network 8 computers.

• It works just like pmli accounts on B37 computers.

• Except you can access them anytime (lunch time, before a course, etc.).

• Note that the disk space allocated for each user is limited to 500 Mo.

• You also have to bring your own mouse or borrow one (caution: 10C).

You can create an account online.

• Go to http://www.student.montefiore.ulg.ac.be/accounts.php

• Provide your ULg registration number2 and ULg password.

Create your account as soon as possible.

You can access your directory from any machine.

2FR: votre matricule, au format sXXXXXX8 / 36

http://www.student.montefiore.ulg.ac.be/accounts.php


Remote access on Network 8

To use Network 8 computers remotely, you’ll need the following software.

• A text editor with code coloration to create and edit your Java code

• A (S)FTP client to transfer your .java files between your computer and the Network 8

• A SSH client to open a remote terminal on a Network 8 computer

Some good text editors

• Windows - Notepad++

• macOS - TextWrangler

• GNU/Linux - Geany

• Alternatively, on Debian/Ubuntu, you can use gedit.

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http://notepad-plus-plus.org/

http://www.barebones.com/products/textwrangler/

http://www.geany.org/


File transfer with Network 8

You have to use the SFTP protocol to transfer your .java files on Network 8.

Simplest method: use FileZilla .

FileZilla is available for any common operating system.

Note for macOS and GNU/Linux

Debian/Ubuntu - filezilla package.

Another solution (“expert” level):

$ scp [-r] files [email protected]:remote_dir

Further information: man scp.

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https://filezilla-project.org/


Network 8 - FileZilla

FileZilla GUI (Graphical User Interface) (under Windows)

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Network 8 - FileZilla (II)

(1) FileZilla log: displays the connexion and operations in details.

• Fast connection form (see next slide) is located just above.

(2) Local file system: your file system, in a tree view.

(3) Remote file system: file system of the remote host (after connection).

(4) Local directory: displays the content of one of your directories.

• Do a double left click on a file to send it (right click for more options).

(5) Remote directory: does the same for a directory on the remote host.

• Do a double left click on a file to download it (right click for more options).

(6) Queue: if you handle several files at once, displays the transfer queue.

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Network 8 - FileZilla (III)

Example of connection to ms803 by the student user:

Host (1): sftp://ms803.montefiore.ulg.ac.be

Username (2): student

Password (3): password

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Network 8 - FileZilla (IV)

This message usually appears at your first connection.

You just have to check the box to avoid this message.

Note: this message will pop for each distinct ms8xx.

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Network 8 - Remote terminal

You have to use the SSH protocol to open a remote terminal on Network 8.

Windows - Use PuTTY , a free SSH client.

macOS and GNU/Linux - Use the ssh command.

In any case, you will have to use command lines. If you are new to them:

• A short tutorial (in French) .

• Pay attention to the commands: man, ls, cd, mkdir, pwd, mv, cp, less and rm.

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http://www.chiark.greenend.org.uk/~sgtatham/putty/

http://doc.ubuntu-fr.org/tutoriel/console_ligne_de_commande


Network 8 - PuTTY

Unlike most programs, you don’t have to install PuTTY.

You might however get a security warning when running it.

Accept to run the program.

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Network 8 - PuTTY (II)

A small window with a lot of menus will open.

Type the address of a Network 8 machine in "Host" and click on "Open".

• In the example, ms801.montefiore.ulg.ac.be.

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Network 8 - PuTTY (III)

Like with FileZilla, you will get a small warning.

Just tell you trust the remote host by clicking "Yes".

This happens only once for each ms8XX machine.

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Network 8 - PuTTY (IV)

A terminal will open. Enter your credentials3.

You can now interact with the remote host with command lines.

3FR: identifiants de connexion19 / 36


Network 8 - ssh command

Just run this command:

$ ssh [email protected]

Replace student with your Montefiore username.

Replace XX with two digits matching a machine (01 to 18).

If a security warning appears, just reply "yes" to continue connecting.

Enter your password and you’re set to interact remotely with Network 8.

Linux - If ssh command is not recognized, install OpenSSH.

$ sudo apt-get install openssh-client

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Network 8 - ssh command (II)

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Beware of plagiarism !

On Network 8, anyone can access your user directory !

Hopefully, you can create directories that only you can access and manage.

Create one for your Java files (for instance: INFO0062).

Protect this directory with the appropriate rights, using this command:

$ mkdir INFO0062 && chmod 700 INFO0062

Verification:

$ ls -l...drwx------ 7 student student 4096 12 fév 02:54 INFO0062...

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Java SE installation


Java SE installation

Windows/macOS:

• Download and installation of the JRE

• Download and installation of the JDK

GNU/Linux:

• The links above offer archives compatible with any distribution.

• For an easiest solution, take a look at the repositories of your distribution.

• You can also take a look at the documentation (or the wiki) of your distribution.

• Procedure for Ubuntu (or derived)

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http://www.oracle.com/technetwork/java/javase/downloads/jre8-downloads-2133155.html

http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html

http://www.webupd8.org/2012/09/install-oracle-java-8-in-ubuntu-via-ppa.html


For macOS and Linux users

You will be able to use javac and java in the terminal after installation.

Don’t forget to get a code editor to write your code (if not using Eclipse).

• macOS - TextWrangler

• GNU/Linux - Geany

• Alternatively, on Debian/Ubuntu, you can use gedit.

This is the most direct way to code in Java if you use one of these OSes.

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http://www.barebones.com/products/textwrangler/

http://www.geany.org/

Eclipse, an IDE


About Eclipse

Eclipse is an Integrated Development Environment.

It’s a program specifically designed for software development. It provides

• a code editor (with code coloration)

• compilation and debugging tools

• project management, auto-completion, etc.

For those who followed INFO2009 or INFO0946, it’s like Code::Blocks.

Eclipse is a very simple solution to program in Java under Windows.

• macOS/Linux users can use it too, but using java/javac is a simpler approach.

• Eclipse can however be arguably more practical for large-scale projects.

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Installation

Download URL

Choose “Download Packages”.

Choose “Eclipse IDE for Java Developers”.

Be careful, you must not take the Java EE edition !

• EE = Enterprise Edition

GNU/Linux - Take a look at the repositories of your distribution.

Debian/Ubuntu - download and install eclipse package.

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http://www.eclipse.org/downloads/


Project creation

Click on the black arrow delimited by the red frame.

Choose “Java Project”.

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Eclipse project creation (II)

Enter your project name (1).

Click on “Finish”.

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Program execution

Press the play button (no argument).

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Program execution (II)

Choose “Java Application”.

Click on “OK”.

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Eclipse project on Network 8 - How can I test my project ?

Suppose that you want to test an Eclipse project on Network 8.

By default, Eclipse creates a bin and a src folder for each project.

You just have to transfer the src folder and run javac on its files.

On a remote terminal, you can just run these commands:

$ javac src/*.java$ java -cp src MyMain

You can create and use a bin directory to isolate .class files from .java files.

$ mkdir bin$ javac -d bin src/*.java$ java -cp bin MyMain

Note: each time you modify your code, you have to re-transfer the edited files.

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About Linux


A few words on Linux

At this point in your cursus, you have heard about Linux a lot.

• Teacher(s) introduced you to the Linux terminal and its command lines.

• You most probably had laboratory sessions with Linux distributions.

• ... and maybe some zealots tried to convert you to Linux !

Why is it a big deal in computer science ?

• Most Linux distributions are free.

• Programming under Linux is usually much easier.

• This is especially true for simple programs.

• With practice, using a terminal is also handier4 than a GUI.

Computer scientists should consider using Linux.

4FR: plus pratique, plus commode32 / 36


How can I use Linux ?

You can use Linux without modifying or dumping your current OS.

• Running a Linux distribution in a virtual machine (FR)

• Using a bootable USB stick (EN)

You can also dual boot (FR) your computer.

• Both your original OS and Linux will co-exist on your computer.

• You will select the OS to run when powering-up your computer.

• Requires to partition your disk space.

• Don’t do this immediatly if you are unsure about your disk.

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https://openclassrooms.com/courses/reprenez-le-controle-a-l-aide-de-linux/installez-linux-dans-une-machine-virtuelle

https://tutorials.ubuntu.com/tutorial/tutorial-create-a-usb-stick-on-windows

https://soozx.fr/installer-ubuntu-dual-boot-windows-10/


Which Linux distribution should I pick ?

Typically, Ubuntu ("Linux for human beings") is recommended for beginners.

• Has a complete GUI for browsing files and running programs, and even a store

• Terminal is not essential for a beginner to use it

Other popular distributions with GUI you can use

• Mint

• Fedora

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https://linuxmint.com/

https://getfedora.org/

Summary


Summary

Consider doing the following steps after this session:

• Install Java (JRE + JDK) on your own machine.

• Consider installing Eclipse if you are a Windows user.

• Create a Network 8 account.

• Download the software you need for remote interaction.

• On your Network 8 folder, create a protected directory for your .java files.

• Create a test program, then try it on the Network 8.

What kind of test program can I do ?

• Simply create a Test class (or any other name) with a main() method.

• Inside the method, print some text with System.out.println().

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Example of a test program

public class Test{

public static void main(String[] args){

System.out.println("Livin’ easy, livin’ free");System.out.println("Season ticket on a one way ride");System.out.println("Asking nothing, leave me be");System.out.println("Taking everything in my stride");System.out.println("Don’t need reason, don’t need rime");System.out.println("Ain’t nothing I would rather do");System.out.println("Going down, for a time");System.out.println("My friends are gonna be there too\n");System.out.println("I’m on the highway to hell");

}}

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