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Java
ACO101: Introduction to
Computer Science
The History of Java
• Started out as a research project at Sun
Microsystems in 1991
• Code named “Green”
• Based on C and C++
• Originally called “Oak” because its creator
James Gosling had an oak tree outside his
office window at Sun.
History of Java – part 2
• They had to change the name from “Oak” to
something else because it was discovered that
there was already a language called “Oak” .
• A group of people at Sun went for coffee one
day and someone suggested “Java” and it
stuck.
• Between 1991 and 1993 the project faltered
because Sun had anticipated that the smart
consumer device market would grow faster
than it did.
Java History – part 3
• When the internet boomed in 1993 the
project got a new life because people saw the
potential to create dynamic content for the
web.
• “Java” was officially announced in May 1995.
Religious discussion
• Java vs. C#
• James Gosling and Bill Joy (one of the
founders of Sun Microsystems) called C# an
"imitation" of Java;
• Gosling (originator of Java) further claimed
that "[C# is] sort of Java with reliability,
productivity and security deleted."
More religious debate
• Klaus Kreft and Angelika Langer (authors of a
C++ streams book) stated in a blog post that
"Java and C# are almost identical
programming languages. Boring repetition
that lacks innovation."
• Anders Hejlsberg (lead the C# team) has
argued that C# is "not a Java clone" and is
"much closer to C++" in its design.
Why do you care?
• Because you will have to decide where you are
in the debate and that will inform your career
path.
• http://www.sun.com/lawsuit/
• http://www.theregister.co.uk/2010/08/13/ora
cle_sues_google/
• http://regmedia.co.uk/2010/08/13/oracle_co
mplaint_against_google.pdf
Technology is constantly
moving forward
• And so you will move forward with it.
• I will not tell you what to think or how to be; I
will only give you the information to decide
for yourself.
Knowing Both
• They are so similar that
– If you know Java then you pretty much know C#
and knowing both will double your job
opportunities.
• http://www.indeed.com/
• Programming is one of the professions that
the more you know the more you earn.
Runtime environments
Java
• Java Runtime Environment
– Includes the JVM and
Common Code Libraries
• JVM = Java Virtual Machine
• The JRE was originally
designed to support
interpreted execution with
final compilation as an
option.
• The Java compiler produces
Java bytecode
C#
• Common Language Runtime
• The CLR is designed to
execute fully compiled
code.
• The C# compiler produces
Common Intermediate
Language instructions.
Program execution
Java
• bytecode is loaded by the
Java runtime and either
interpreted directly or
compiled to machine
instructions and then
executed
C#
• the runtime loads Common
Intermediate Language
code and compiles to
machine instructions on the
target architecture
Side bar: bytecode and CIL
instructions
• A Java programmer does not need to be aware
of or understand Java bytecode at all.
• However, "Understanding bytecode and what
bytecode is likely to be generated by a Java
compiler helps the Java programmer in the
same way that knowledge of assembler helps
the C or C++ programmer.“ – Peter Haggar IBM
• The same is true for CIL instructions and C#
We are not going that deep.
• If you are interested – here are some links; but
this is Intro and you are not required to
understand bytecode, CIL instructions or
machine code on a deeper level.
– http://www.ibm.com/developerworks/ibm/library
/it-haggar_bytecode/
– http://en.csharp-online.net/CIL_Instruction_Set
Lets check to see if
the JDK is installed
• Go to Start > Run > type “cmd” in the box to
launch a command prompt
– Type in the window (where the cursor is)
java –version
• C:\Program Files\Java
– Is there a folder named jdk1.6.0_21
• click into the bin in that folder
– C:\Program Files\Java\jdk1.6.0_21\bin
– javac.exe is the compiler
To DIY you will need
• The Java SE Development Kit 6 (JDK 6)
– http://www.oracle.com/technetwork/java/javase/
downloads/index.html
– Read the installation instructions
• http://www.oracle.com/technetwork/java/javase/index
-137561.html
– Click on the Download JDK button
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I registered (you don’t have to)
Pick your platform and click continue
Click on the link provided to download the exe
Save file, double click and run
Follow the installation wizard
Next
next
Close browsers
finish
This is optional
Hello world
• We havta do the tradition…. It would be just
wrong to not have your first program be
“Hello World”
• Open notepad (on a mac you can use simple
text) and type this code…..
class myfirstjavaprog
{
public static void main(String args[])
{
System.out.println("Hello World!");
}
}
Save as….
• myfirstjavaprog.java
Bring up a command prompt
Start > Run > cmd
Change the directory to the
location of javac
Now send the location of your .java
file to the compiler
Now go check to see if you have a
.class file (you should)
Let’s run it – go to the location of the class
(current working directory) and pass the name of the
class to the Java runtime
Success!
Homework
• Is posted on the class portal 