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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 .

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The java application
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


  • 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



  • Comments

    // for a line of comment

    /* for multiple

    lines */


Java Documentation Comments:

  • Doc comment --- special type of JAVA comment

  • A multi line comment starts with /** (insead of /*) & Ends with */


Java Documentation Comments:

  • These comments can be turned into online HTML documentation by the javadoc program

    EXAMPLE:

    /**

    * @ author David Farrell

    * @version 1.0


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


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


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


Class:

The initial class as a wrapper for the entry point to the java application (SPVM)

public class HelloWorld

{


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

}

}


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


Import:

import javax.swing.JOptionPane;

  • We now have Access to all the methods of JOptionPane


Import:

  • OPEN UP JAVA DOC & GO TO javax swing JOptionPane

    & look at the showInputDialog

    method


Semi-Colon:

  • End of Code segment identified by a semi-colon ;


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 )


Syntax and Style:

  • Java is case sensitive

  • Redundant whitespace is ignored

  • Use blank lines, indenting for better reading of the code


Syntax and Style:

  • Compiler catches most syntax errors, but not logic errors “bugs”

  • Java statements and declarations usually end in a semi-colon


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.


Syntax and Style:

  • Start ALL class names with a capitol letter (use names that are nouns)

    String

    StringBuffer

    JOptionPane

    System


Syntax and Style:

  • Instances of objects start in Lower Case

    String myString

    String firstNumber


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( )


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


Syntax and Style:

  • Use all Upper Case for constants

    final int MAXPOINTS = 200;


Syntax and Style:

  • Line up the brackets { }

  • Brackets identify the beginning of

    A class

    A method

    A code block (like if and endif)


  • 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 );

    }

    }


  • 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 !!!


  • Project:

  • Code the 4 projects directly from the handouts

  • Be able to identify all of the parts of the program that we covered


  • 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


  • Project:

  • View the JAVA Doc and look at some of the methods and classes we used


TEST IS THE DAY AFTER THE PROJECT IS DUE !!!


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