An introcution to,Java. What are JDK, JRE, JVM? Where to start? This presentation is a brief introduction to Java development and how to set a developer's environment properly.

1. Java goes wild
Lesson 1: Introduction to Java
Thierry Wasylczenko

2. After this course ...
You will:
• Know what is the JDK/JRE
• Be able to set up your development environment
• Know how to compile and run a Java program
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3. Agenda
• Bascis
• How does all of this work?
• Developer’s environment
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4. Basics
Success is neither magical nor mysterious. Success is the natural
consequence of consistently applying the basic fundamentals.
Jim Rohn “
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5. Basics
• Source code is inside files with .java extension
• The source code is compiled into .class files
• The class files are executed by a strange thing (covered later)
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6. A Java file
public class Foo {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}
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7. How do I get class files?
• By compiling all Java files
$ cd /location/of/java/files
$ javac Foo.java
$ ls
Foo.class Foo.java
$
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8. How do I run it?
• With the java command
$ java Foo
Hello World!
$
• Yes you DON’T put the .class extension when you run a class !
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9. Java Archive
• aka JAR
• A collection of compiled Java classes
• Package of a Java program
• Can be runnable
java -jar Foo.jar
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10. That's
freaking
AWESOME !

11. That’s awesome dude. But how
does all of this work?
You “
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12. 12
How does all of this work?
It is not the beauty of a building you should look at; it's the construction
of the foundation that will stand the test of time.
David Allan Coe “

13. The source code
• Plain text file
• File extension: .java
• Rules for naming each file (covered later)
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14. The bytecode
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• Result of compilation
• Something in between the source code and the machine’s language
• Interpreted by the Java Virtual Machine

15. The Java Virtual Machine
• aka the JVM
• Kind of a black box
• Interprets the Java bytecode
• Is available on major platforms
• "Compile once, run everywhere"
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16. A little schema
Source
code
Source
code
Byte code JVM
Byte code JVM
turns on
turns on
java
java
javac
javac
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17. Well man, you’re talking about
JVM, javac, bytecode and cool
stuff. But how do I set them up?
You “
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Developer's environment
When people think about computer science, they imagine people with
pocket protectors and thick glasses who code all night.
Marissa Mayer “

19. Java Development Kit
• aka JDK
• Provides tools
• javac: java compiler
• javadoc: generates the documentation
• ...
• Includes a Java Runtime Environment
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20. Java Runtime Environment
• aka JRE
• Provides tools:
• java: for running Java applications
• ...
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21. JAVA_HOME
• An environment variable
• Points to the JDK installation
• Required by some tools such as:
• IDEs
• build tools (maven, gradle, ...)
• ...
• Used to update the PATH variable
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22. JAVA_HOME: example
# Unix
export JAVA_HOME="/path/to/jdk"
export PATH=$JAVA_HOME/bin:$PATH
REM Windows
set JAVA_HOME="C:pathtojdk"
set PATH=%JAVA_HOME%bin;%PATH%
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23. Avoid spaces in the path of your
JAVA_HOME.
JAVA_HOME
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24. JAVA_HOME: test the setup
To test the setup you can execute the following command:
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$ java -version
java version "1.8.0_11"
Java(TM) SE Runtime Environment (build 1.8.0_11-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.11-b03, mixed mode)

25. What does JRE stand for?
• Java Runtime Embeded
• Java Routine Exclusive
• Java Runtime Environment
Start Stop
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26. What is the correct command to
execute a Java program?
• java Foo.java
• java Foo
• java Foo.class
Start Stop
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27. 1. Set the JAVA_HOME in your
environment
2. Verify your setup
Practice #1
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28. Practice #2
Given the following code:
public class Foo {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}
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29. 1. Copy it in your favorite editor
2. Save the file as Foo.java
3. Compile it
4. Run it
Practice #2
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31. 31
Appendix

32. Appendix
• Java Code conventions
• Not maintained since 1997, may not be accurate
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