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The JAVA Application
Java Applications are similar to C++
programs in that they require a MAIN
entry point. However, unlike C++ or
Visual Basic, Java Applications require
everything emanate from a CLASS.
We will code examine several Java
applications. We will also discuss
appropriate coding style and naming
conventions
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GOALS...
To identify ALL of the main parts
of a Java Application, Syntax
Errors
To code simple applications
using the proper Syntax, Style
and naming Conventions
To get comfortable with Code
Warrior, Java API Document
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Breakdown of the Java Application:
Use our HelloWorld and other
applications handed out as a
reference
HINT: write comments on these
handouts !!!
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Comments
// for a line of comment
/* for multiple
lines */
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Java Documentation Comments:
Doc comment --- special type of
JAVA comment
A multi line comment starts with
/** (insead of /*) & Ends with */
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Java Documentation Comments:
These comments can be turned into
online HTML documentation by the
javadoc program
EXAMPLE:
/**
* @ author David Farrell
* @version 1.0
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Public Static Void Main:
The main entry point in a Java
Application
The first code to execute
Actually, it is a wrapper for the Java
Class that is to execute first
The classname that has PSVM MUST
match the filename
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Standard Output Stream:
Used to send output to the console
System.out.println(“Hello World”);
Standard Java API method from the
Java.Lang.System class
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Standard Output Stream:
Static Method (does not require
instance of System class)
OPEN UP JAVA DOC AND GO TO
java Lang System and look at
the out exit gc & sleep
methods
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Class:
The initial class as a wrapper
for the entry point to the
java application (SPVM)
public class HelloWorld
{
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Class Constructor:
The method that gets executed when
an instance of a class is created
Public class Addition
{
public Addition( ) // empty constructor
{
}
static public void main (String args[ ] )
{
new Addition( ) ; // calls the class constructor
}
}
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Import:
Brings in the prewritten classes for
us to use / leverage in our
application
vital OO benefit
•provides conformity &
reusability
•Like Adding a component in
Visual Basic
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Import:
import javax.swing.JOptionPane;
We now have Access to all
the methods of JOptionPane
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Import:
OPEN UP JAVA DOC & GO TO
javax swing JOptionPane
& look at the
showInputDialog
method
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Semi-Colon:
End of Code segment identified by
a semi-colon ;
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CW debugger (again):
Open up the various projects
created and use the debugger and
Make changes to cause syntax /
compile errors
Look at how these messages are
displayed
System or Exception Errors ( try &
catch )
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Syntax and Style:
Java is case sensitive
Redundant whitespace is ignored
Use blank lines, indenting for
better reading of the code
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Syntax and Style:
Compiler catches most syntax
errors, but not logic errors “bugs”
Java statements and declarations
usually end in a semi-colon
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Syntax and Style:
All Java reserved words are in Lower Case
(see handout)
boolean
char
int null
new
true
false
public
private protected
static
class
import
if
try
catch
Reserved words must be spelled
exactly.
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Syntax and Style:
Start ALL class names with a
capitol letter (use names that are
nouns)
String
StringBuffer
JOptionPane
System
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Syntax and Style:
Instances of objects start in Lower
Case
String myString
String firstNumber
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Syntax and Style:
Start all method names with Lower
Case, then Upper Case remaining
words (first word as a verb –
action)
println( )
parseInt( )
insert( )
insertObject( )
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Syntax and Style:
Start all names of variables with a
Lower Case letter and subsequent
words start w/ Upper Case
int number;
Can’t start with a digit.
Use self-explanatory names and
follow a naming convention
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Syntax and Style:
Use all Upper Case for constants
final int MAXPOINTS = 200;
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Syntax and Style:
Line up the brackets { }
Brackets identify the beginning of
A class
A method
A code block (like if and endif)
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Indent the Correct way:
public class Sample
{
public static void main(String[] args)
{
int anumber = 23;
for(int x=0; x < 10; x++)
{
anumber += x;
}
System.out.println( anumber );
}
}
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Indent the Wrong way:
{
public class Sample {
public static void main(String[] args)
int anumber = 23;
for(int x=0; x < 10; x++){
anumber += x; }
System.out.println( anumber ); } }
Which one is easier to debug !!!
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Project:
Code the 4 projects directly from
the handouts
Be able to identify all of the parts
of the program that we covered
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Project:
Use the debugger and make coding
changes , once the program works
as intended, see and fix the compile
errors
Implement the System methods
exit gc & sleep in one or more of
these programs
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Project:
View the JAVA Doc and look at
some of the methods and classes
we used
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TEST IS THE DAY
AFTER THE
PROJECT IS DUE
!!!
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