Download Computer Programming 12

Computer Programming 12
Mr. Jean
March 3rd, 2014
The plan:
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Video Clip of the day
Why Java?
Using Jcreator
Learning how to create a project in
Jcreator
2.1 Why Java?
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Java is the fastest growing
programming language in the world.
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Java is a modern object-oriented
programming language.
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Java has benefited by learning from
the less desirable features of early
object-oriented programming
languages.
2.1 Why Java?
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Java is ideally suited to develop
distributed, network-based
applications because it:
– Enables the construction of virus-free,
tamper-free systems (security)
– Supports the development of programs
that do not overwrite memory (robust)
– Yields programs that can be run on
different types of computers without
change (portable)
2.1 Why Java?
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Java supports advanced programming
concepts such as threads.
– A thread is a process that can run
concurrently with other processes.
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Java resembles C++, the world’s most
popular industrial strength
programming language.
Java however, runs more slowly than
most modern programming languages
because it is interpreted.
2.2 The Java Virtual
Machine and Byte Code
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Java compilers translate Java into
pseudomachine language called java
byte code.
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To run java byte code on a particular
computer, a Java virtual machine
(JVM) must be installed.
2.2 The Java Virtual
Machine and Byte Code
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A Java virtual machine is a program
that acts like a computer. It is called
an interpreter.
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Disadvantage:
– Runs more slowly than an actual
computer
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To combat slower processing, some JVMs
translate code when first encountered. This is
known as just-in-time compilation (JIT).
2.2 The Java Virtual
Machine and Byte Code
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Advantages:
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Portability. Any computer can run Java byte
code.
Applets. Applets are small Java programs
already translated into byte code.
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Applets run in a JVM incorporated in a web browser
Applets can be decorative (like animated characters on
a web page.)
Applets can be practical (like continuous streams of
stock market quotes.)
Security. It is possible to limit the capabilities of
a Java program since it runs inside a virtual
machine.
How to build new projects:
Today’s Goals:
• We will be introduced to classes and
static methods and are shown how to
compile and run a Java program.
First Program in Java
• This simple program causes the word
“Hello” to be printed.
• To start:
– Find jcreator on your computer
– Open jcreator and copy to code from my PPT
onto your jcreator
J-creator Video:
• http://www.youtube.com/watch?v=Bmryow
3NYPE (Getting Started)
• http://www.youtube.com/watch?v=SMHK3
oO8zLg (Hello World)
• http://www.youtube.com/watch?v=3u1fu6f
8Hto (About Java & Applications)
Compiling & Running a program
• A Java program must be compiled before
it can be run by the Java system (Java
Virtual Machine).
– The complier translates the Java program into
the underlying Java machine language (called
Java byte codes) and creates a file containing
the result.
– This file (also called the class file) is used by
the Java system to run (or execute) the
program producing the program output.
• When the program is run the system looks for
the main method and begins with the first
instruction and then the further instructions in
order. Most methods contain many instructions.
• In Java instructions are called statements.
– Statements are executed.
• The program above contains the single
statement that causes the word (or string) Hello
to be printed.
– System.out.println("Hello");
Creating an error:
• One of the functions of the compiler is to
detect syntax errors.
• Deliberately introduce small syntax errors
and observe the results.
Common Errors:
• When using JavaRoom, if the name of the
class containing the main method is not
the same as the name of the file, the name
of the class must be selected before
clicking the run button.
About our Program:
• Our program consists of a class containing a
main method (a method with the name main).
– the name of the class is HelloTester.
– the class contains a main method which must be
public (otherwise it will not run)
– static(because it is not part of any object)
– void (because it does not return any value).
• In this case the method contains only one
instruction (statement) which is a call to the
println method in the out object in the System
class.
Adding information:
• It is important to tell other programmers
what you are doing
• In order to do this you must start with start
with “/*” and end with “*/”