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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 .

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The JAVA Application

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  1. 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

  2. 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

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

  4. Comments // for a line of comment /* for multiple lines */

  5. Java Documentation Comments: • Doc comment --- special type of JAVA comment • A multi line comment starts with /** (insead of /*) & Ends with */

  6. Java Documentation Comments: • These comments can be turned into online HTML documentation by the javadoc program EXAMPLE: /** * @ author David Farrell * @version 1.0

  7. 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

  8. 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

  9. 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

  10. Class: The initial class as a wrapper for the entry point to the java application (SPVM) public class HelloWorld {

  11. 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 } }

  12. 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

  13. Import: import javax.swing.JOptionPane; • We now have Access to all the methods of JOptionPane

  14. Import: • OPEN UP JAVA DOC & GO TO javax swing JOptionPane & look at the showInputDialog method

  15. Semi-Colon: • End of Code segment identified by a semi-colon ;

  16. 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 )

  17. Syntax and Style: • Java is case sensitive • Redundant whitespace is ignored • Use blank lines, indenting for better reading of the code

  18. Syntax and Style: • Compiler catches most syntax errors, but not logic errors “bugs” • Java statements and declarations usually end in a semi-colon

  19. 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.

  20. Syntax and Style: • Start ALL class names with a capitol letter (use names that are nouns) String StringBuffer JOptionPane System

  21. Syntax and Style: • Instances of objects start in Lower Case String myString String firstNumber

  22. 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( )

  23. 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

  24. Syntax and Style: • Use all Upper Case for constants final int MAXPOINTS = 200;

  25. Syntax and Style: • Line up the brackets { } • Brackets identify the beginning of A class A method A code block (like if and endif)

  26. 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 ); } }

  27. 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 !!!

  28. Project: • Code the 4 projects directly from the handouts • Be able to identify all of the parts of the program that we covered

  29. 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

  30. Project: • View the JAVA Doc and look at some of the methods and classes we used

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

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