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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
slide2
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
slide3
Breakdown of the Java Application:
  • Use our HelloWorld and other applications handed out as a reference
  • HINT: write comments on these handouts !!!
slide4
Comments

// for a line of comment

/* for multiple

lines */

slide5
Java Documentation Comments:
  • Doc comment --- special type of JAVA comment
  • A multi line comment starts with /** (insead of /*) & Ends with */
slide6
Java Documentation Comments:
  • These comments can be turned into online HTML documentation by the javadoc program

EXAMPLE:

/**

* @ author David Farrell

* @version 1.0

slide7
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
slide8
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
slide9
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

slide10
Class:

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

public class HelloWorld

{

slide11
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

}

}

slide12
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
slide13
Import:

import javax.swing.JOptionPane;

  • We now have Access to all the methods of JOptionPane
slide14
Import:
  • OPEN UP JAVA DOC & GO TO javax swing JOptionPane

& look at the showInputDialog

method

slide15
Semi-Colon:
  • End of Code segment identified by a semi-colon ;
slide16
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 )
slide17
Syntax and Style:
  • Java is case sensitive
  • Redundant whitespace is ignored
  • Use blank lines, indenting for better reading of the code
slide18
Syntax and Style:
  • Compiler catches most syntax errors, but not logic errors “bugs”
  • Java statements and declarations usually end in a semi-colon
slide19
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.
slide20
Syntax and Style:
  • Start ALL class names with a capitol letter (use names that are nouns)

String

StringBuffer

JOptionPane

System

slide21
Syntax and Style:
  • Instances of objects start in Lower Case

String myString

String firstNumber

slide22
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( )

slide23
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
slide24
Syntax and Style:
  • Use all Upper Case for constants

final int MAXPOINTS = 200;

slide25
Syntax and Style:
  • Line up the brackets { }
  • Brackets identify the beginning of

A class

A method

A code block (like if and endif)

slide26
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 );

}

}

slide27
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 !!!
slide28
Project:
  • Code the 4 projects directly from the handouts
  • Be able to identify all of the parts of the program that we covered
slide29
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
slide30
Project:
  • View the JAVA Doc and look at some of the methods and classes we used
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