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Introduction to Java
What is Java?
• A computer programming language that can
be run as either an application or an applet.
– What is the difference?
• It is considered to be a high-level language.
• Designed in the early 90’s by a team from ???
• What is the difference between Java and
JavaScript ?
• How did java get its name?
– http://www.javaworld.com/javaworld/jw-101996/jw-10-javaname.fullquote.html
Java is…
• Parsimonious – that is it has a compact set of
commands without numerous versions or changes
• Robust- it supports the development of programs
that do not accidentally overwrite data or corrupt
data
• A Strongly typed language – in that its compiler
provides extensive checking for potential problems
• Secure – its programs are easy to protect from
viruses.
• Portability/platform independent – can be used
on multiple operating systems
Why Learn Java?
• Good Paying Careers
• It’s just a good fun language to know
Java Components
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Program source
Compiler
Bytecode
Interpreter
Java Virtual Machine
Java Runtime Environment
IDE- Integrated Development
Environement
The Java Program Development Life
Cycle
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Analyze the problem
Design the program
Code the program
Test the program
Formalize the solution
Maintain the program
Algorithms
• A clear and unambiguous specification of the
steps needed to solve a problem.
• Correct – using a logical constructs and valid
data in an organized way so that the steps
will be carried out correctly and the program
will make suitable responses to invalid data,
ie warning messages
• Efficient – refers to the program’s ability to
deliver a result in a short time frame to be
useful and using as little memory as possible
Understanding FlowCharts
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Process Symbol
Input/Output Symbol
Flowline Symbol
Annotation Symbol
Decision Symbol
Terminal Symbol
Connecter Symbol
Predefined Process Symbol
Control Structures
• No matter what procedures (or progression of
logical actions) that you wish the computer to
perform they can be broken down into these
three categories
– Sequence Control
– Selection Control
• Case Control
– Repetition Control
• Nested
Java as an Object-Oriented Language
• Still has many different definitions, but
the general concept is to package
functions together while not restricting
data types.
– Ie the open desk example
Object- Speak
• Nouns
– Object – anything real or abstract about
which you both store data and operations
that manipulate the data
– Class- an object or set of objects that
share a common structure and common
behavior.
• Subclass
• superclass
Object Speak Cont
• Generalization hierarchy
– An OO design tool used to show the relationships
among classes
• Data abstraction
– Process of creating new high-level data structures
based on a defined object through a set of
interface operations instead of by directly
manipulating the object
• Instance – unique object or specific
occurrence of a class of objects
– Ie a two-player button
Verbs
• Operation – activity that reads or
manipulates the data of an object.
• Message defines the interaction of the
object
• External trigger
• Process that causes an operation to
occur is an event
– Event diagram page 1.13
Adjectives
• Attributes are identifying characteristics
of individual objects, such as name,
size, or color.
Other terms
• Encapsulation
– Process of hiding the implementation details of an
object from its user by combining attributes and
methods
– Inheritance
• Concept that programmers can use a class along with
functions and data to create a descendent class or
subclass
• Polymorphism
– Allows instructions to be given to an object in a
generalized rather than specific detailed
command, ie where specific actions are different,
results are the same
Lets look at an Actual Java Program
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public class carl
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{
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Project 1 Printing on the screen
Programmer:
Carl Rebman
Date:
4 March 2003
Program Name
Carl
public static void main(String [] args) //method header
{
System.out.println("Carl's Antiques");
System.out.println("208 Olin Hall");
System.out.println("San Diego, CA 92110");
}
How do you run it?
• First step is to have the JDK loaded
• Second step (after program is written)
is to compile the program
– Go to command prompt
– Set prompt to location of JDK compiler
– In this case should be path=c:\jdk1.2.2\bin
– Next change to the directory your program
is in—should be A:\
Running the program cont.
• Once path has been set and proper directory
has been established
• Run compiler
– javac Program_Name.java
• If successful you’ll get the command prompt
again
• If not, you see a list of errors
• When there are no errors, run program by
typing in
– java Progam_Name
So what does the code mean?
• public class Carl {
– A class must be defined in every java program
– Public is used as a modifer that describe other
classes’s access to this class
• This becomes more important as your programs get
more complex
– Basically this line starts your program called Carl,
and the brackets contain its guts
public static void main(String [] args)
• Methods are the groups of statements
that are executed by your computer
when instructed to do so.
• The main method actually drives the
java applications
– It is the first place the Java VM looks when
you run your application
Public versus static
• Public makes this method accessible
from all other classes
• Static ensures there is only one
reference to this method
• Void means that the method does not
return any value when completed
• The Strings[args] means that it is an
array list of command-line arguments
Comments
• Single line—begins with //
• Multiple line begin with /* and end with
*/
Moving up to an Applet
• Again what is an applet?
How to run an Applet
• Type at the command prompt
– appletviewer FILE_NAME.html
Special Code
• import java.awt.Graphics;
– This does actually import a class called Graphics
– This is a previously defined class of which you can
call
• Extends java.applet Applet
– This increases the import and allows for extending
the class
• You get to reuse the functionality of the class
• Which means when class A extend class B, class A
becomes a superclass, and class B becomes a subclass
Now lets write our first JAVA program
• Project 1 in book