Gayle J Yaverbaum, PhD Professor of Information Systems Penn State Harrisburg

OO Concepts Reviewed  Programs consist of communicating objects.  Objects consist of:  fields/data (values or attributes) = properties.  methods= behaviors.  Instantiation = process of creating an object.

More OOP Concepts  Abstract data type (ADT)  Encapsulation  Polymorphism

Java features  Portable  Multithreaded  Secure

Java Graphics/speed ■ JAVA has very good graphics ■ Applets provide access to Graphical User Interface (GUI) ■ JAVA is fast ■ Better Support in recent years

JAVA Development Environment Eclipse 3.2  Review tutorial-March 1  Use for applet development

Each JAVA Applet extends or inherits the JApplet class Methods in JApplet class do nothing unless overriden: init : called automatically when applet is run start: automatically called after init paint: called once after init, when a panel changes, and also after repaint () method is called stop: called when execution is finished destroy:cleans up after applet removed from memory

Business KMartMacys ServiceBusiness Kinkos RetailBusiness The child inherits characteristics of the parent: (both methods and data) Note: Single inheritance in JAVA is-a

An Applet Sample Structure import javax.swing.*; //programs are derived // from javax.swing import java.awt.*; //abstract windows toolkit public class extends JApplet { public void init () { } public void paint (Graphics g) { }

Lab: Applet I CREATE A PROJECT in Eclipse ( Tutorial (if review is necessary) Tutorial I. File/New/Project/Java/JavaPr oject/Next/Finish Project Name: FirstApplet, in the appropriate space.

Lab: Applet I CREATE A Package in the project I. File/New/Package II. Enter a Package Name: fi rstapplet, in the appropriate space III. Finish

Lab: Applet I Create a class within the package Caution: Do not check any buttons on bottom of the screen Right Click on the package name Create a class Enter the Name: of the class – call it FirstApplet Finish

Lab: Applet I package firstapplet; public class FirstApplet { } Extend the class so that it will inherit methods from JApplet public class FirstApplet extends JApplet Add two import statements after the package statement: import javax.swing.JApplet; import java.awt.*; Your screen!

package firstapplet; import java.swing.JApplet; Import java.awt.*; public class FirstApplet extends JApplet { } You will see something similar to this!

package firstapplet; import java.awt.*; Import javax.swing.JApplet; public class FirstApplet extends JApplet { public void init () { } public void paint (Graphics g) { } Add the following within the class!

Save your program 1.Right Click on FirstApplet Project 2.Build project 3.Run 4.Run As 5.Java Applet

Applet Demo Explanation

Add some code! (use your own string values and color) package firstapplet; import java.awt.*; Import javax.swing.JApplet; public class FirstApplet extends JApplet { public void init () { } public void paint (Graphics g) { super.paint (g); Graphics2D g2 = (Graphics2D)g g2.setColor (Color.blue); g2.drawString (“Gayle J Yaverbaum”, 20, 10); g2.drawString (“Penn State Harrisburg”, 20,25); } Caution: DO NOT cut and paste from Powerpoint

Applet Demo Explanation 1. init : is called automatically when applet is run 2.paint: is called once after init and when a repaint method is called. a.super.paint (g) calls the super class inherited from JApplet. Omitting it can cause some subtle drawing errors. b.paint receives the Graphics class as a parameter.

The form is (type) public void draw (Graphics g) { Graphics2D g2=(Graphics2D)g; } Casting: to convert the object "g" to "g2"

 A Graphics object is passed as a parameter to paint ()  setColor is a method in the Graphics class  black (default), blue, cyan, darkGray, gray, green, lightGray, magenta, orange, pink, red, white, and yellow  drawString is a method in Graphics  Parameters are: string, x coordinate, y coordinate

Reminders!  FirstApplet is name of class and must be same as the class name  By convention - class names begin with a capital letter  By convention - package names are the same name as the project name and all lower case  By convention method names begin with a lower-case letter

xml file for FirstApplet Of note!

XSLT

DTD: Element with attributes <!ATTLIST app class CDATA "none" class CDATA "none" width CDATA "none" width CDATA "none" height CDATA "none" height CDATA "none"> <!ATTLIST elementname attributename type default CDATA means character string

Reviews Text: Chapter 7 Reviews A Team Home Page A member Home Page One Applet Page 2..4 sub pages

Extending the Application  DrawClass  Create another class, DrawClass, in your project package  Use the same package name, firstapplet, as before  Create a method, draw, in the class  Draw receives the Graphics class from the calling method

public class DrawClass { public void draw (Graphics g) { }

public class FirstApplet extends JApplet { DrawClass d; public void init () { d = new DrawClass (); } public void paint (Graphics g) { super.paint(g); Graphics2D g2=(Graphics2D)g; g2.setColor (Color.blue); g2.drawString ("Gayle J Yaverbaum", 50, 20); g2.drawString ("Penn State Harrisburg", 50,30); d.draw(g); }

public void draw (Graphics g) { super.paint(g); Graphics2D g2=(Graphics2D)g; g2.setPaint (Color.red); g2.setStroke( (new BasicStroke (10.0f))); g2.draw (new Rectangle2D.Double(100, 50, 100,50)); } Sun Java Tutorial on 2D Graphics Draw Method Ideas