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Published byKaylee Larman Modified over 10 years ago
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Gayle J Yaverbaum, PhD Professor of Information Systems Penn State Harrisburg
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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.
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More OOP Concepts Abstract data type (ADT) Encapsulation Polymorphism
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Java features Portable Multithreaded Secure
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Java Graphics/speed ■ JAVA has very good graphics ■ Applets provide access to Graphical User Interface (GUI) ■ JAVA is fast ■ Better Support in recent years
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JAVA Development Environment Eclipse 3.2 Review tutorial-March 1 Use for applet development
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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
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Business KMartMacys ServiceBusiness Kinkos RetailBusiness The child inherits characteristics of the parent: (both methods and data) Note: Single inheritance in JAVA is-a
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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) { }
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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.
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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
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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
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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!
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package firstapplet; import java.swing.JApplet; Import java.awt.*; public class FirstApplet extends JApplet { } You will see something similar to this!
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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!
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Save your program 1.Right Click on FirstApplet Project 2.Build project 3.Run 4.Run As 5.Java Applet
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Applet Demo Explanation
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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
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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.
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The form is (type) public void draw (Graphics g) { Graphics2D g2=(Graphics2D)g; } Casting: to convert the object "g" to "g2"
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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
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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
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xml file for FirstApplet Of note!
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XSLT
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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
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Reviews Text: Chapter 7 Reviews A Team Home Page A member Home Page One Applet Page 2..4 sub pages
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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
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public class DrawClass { public void draw (Graphics g) { }
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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); }
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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
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