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The JAVA ApplicationJava 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 createdPublic 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 charint nullnew true falsepublic private protectedstatic class importif 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)

StringStringBufferJOptionPaneSystem

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Syntax and Style:

Instances of objects start in Lower Case

String myStringString 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 classA methodA 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 !!!