Inheriting the JFrame

1. Inheriting the JFrame

2. Three ways to make use of classes • 1. Using a static class (no need to create an object): myStr = String.toLowerCase( “ABCDE ); myInt = Integer.parseInt( “14” ); JOptionPane.showMessageDialog( null, “Hello” ); • 1a Using a non-static class (new, but no oject) new AnyClass( ); // essentially, just to run the // constructor

3. Second way: Create objects • 2. One step instantiation: JFrame myWindow = new JFrame( ); • 2.a. Two step Instantiation: public JFrame myWindow; public static void method( int a) { myWindow = new JFrame( ); … }

4. third way: public class myClass extends JFrame { // your class inherits all of JFrame’s // methods }

5. Extension, Hierarchy, and Inheritance

6. Extension, Hierarchy, and Inheritance • Extends – in the class statement, tells which larger class serves as the “parent”. • Inheritance – the child class inherits methods and variables from the parent class • Hierarchy - parent to child relationship

7. Extend keyword public class myClass extends someOtherClass { // I can use all the methods and // variables from someOtherClass in myClass. }

8. Other terms • Parent / Child • Base class / Sub class • Super Class / Sub class • Any class (not just an imported library class) can be a parent or base class. • Write classes – then write new inherited classes for targeted capabilities.

9. Java common inherited classes • public class myClass extends JFrame - myClass gets a whole bunch of methods for displaying windows on-screen including the ability to launch a paint( ) method. • public class myClass extends Applet - applet and browser graphics • public class myClass extends Object - the parent of ALL classes, usually omitted

10. import javax.swing.*; public class MainClass extends JFrame { // stuff here public static void main (String [ ] args) { MainClass application = new MainClass( ); } }

11. JFrame Sept 18: • Puts graphics-capable windows on screen. • JOptionPane uses JFrame • Colors • Fonts • Drawings • A frame for intuitive GUI • Adds a paint method

12. Use these helper libraries import javax.swing.JFrame ;// for JFrame import java.awt.* ;// for painting and animation import java.awt.event.* ;// for “event” handling, more later import java.util.Random ;// always useful

13. some JFrame methods • setLocation(100,200); • setSize(250,250); • setVisible(true); • setDefaultCloseOperation( EXIT_ON_CLOSE)

14. public class MainClass extends JFrame { public MainClass ( ) { setLocation(100,200); setSize(250,250); setVisible(true); }// end MainClass constructor public static void main (String[] args) { MainClass application = new MainClass( ); } // end main method } // end class

15. public class MainClass extends JFrame { public MainClass ( int x, int y ) { setLocation( x, y ); setSize(250,250); setVisible(true); }// end MainClass constructor public static void main (String[] args) { MainClass application = new MainClass(100, 200); } // end main method } // end class

16. public class MainClass extends JFrame { public MainClass ( int x, int y ) { setLocation( x, y ); setSize(250,250); setVisible(true); }// end MainClass constructor public static void main (String[] args) { MainClass appl1 = new MainClass(100, 200); MainClass appl2 = new MainClass(200, 300); } // end main method } // end class

17. Demo

18. If you don’t extend JFrame…. public class MainClass { public MainClass ( ) { JFrame myFrame = new JFrame( ); myFrame.setLocation(100,200); myFrame.setSize(250,250); myFrame.setVisible(true); }// end MainClass constructor public static void main (String[] args) { MainClass application = new MainClass( ); } // end main method } // end class

19. Objects As Containers of Information

20. Objects don’t always DO things • Sometimes they just HOLD things (information) • The Color class can hold color information • The Point class can hold cartesian coordinate information • The Container class contains 10,000 variables that describe your computer

21. Color class Holds a color value (nothing more) e.g Color boxColor = new Color( redInt, greenInt,blueInt); boxColor = Color.blue; or Color boxColor = Color.blue then boxColor can be used to set System properties in Classes/Objects that need color.

22. How do you define a color?

23. JColorChooser – returns a Color object to the caller

24. Returns an Object? • JColorChooser fills in all of the information in a blank object of the Color class, and copies it to the Color object in the calling statement: boxColor = JColorChooser.showDialog( null, Greeting, default color );

25. the Point class • holds an x,y value (nothing more) Point screenLocation = new Point( ); screenLocation.x = 100; screenLocation.y = 200;

26. the this qualifier • Means “this object, the one that we’re in”. • Used when a call to a method, especially in a child, needs to specify which object the method should act upon. • this always refers to an object or class of some type.

27. the super qualifier • refers to the parent class • the command super calls the parent’s constructor • super.MethodName can call any method in the parent.

28. graphics on “your computer” • Since there are many computers (types, instances).... • and since the programs that you write should run anywhere.... • then the programs that you write, should retrieve and use information native to the computer that it is running on. • This is called “context awareness”

29. The paint Method • Computer runs it once (you don’t), but then you can run it by calling repaint();. • The computer passes it an object of the Graphics Class, of it’s own making.

30. public void paint (Graphics g) { // the computer calls the paint program // automatically whenever an event requires // the screen to be redrawn }

31. An “event” • The user does anything: moves the mouse, moves the window, hits a key, etc.

32. Graphics! • g.setColor • g.fillRect • g.drawString • g.drawPolygon • hundreds of methods that use your computer’s graphics capability

33. demo • A Frank Lloyd Wright style generator

34. imports import javax.swing.*;import java.awt.*;import java.util.Random;public class FLWPainting extends JFrame { public int x=0, y=0, width=0, height=0, red=0, green=0, blue =0; public Random myGen = new Random(); public int calls = 0; public int size = 800;

35. Constructor public FLWPainting(){setSize( size, size );setLocation( 10, 10 );setVisible( true );setDefaultCloseOperation( EXIT_ON_CLOSE); }// end constructor

36. paint // "paint" is a method already in JFrame// it's called automajically by the computer// it uses the Graphics helper class// I'm rewriting it// That's called over-ridingpublic void paint( Graphics g ) {g.setColor( Color.white ); g.fillRect(0, 0, size, size);

37. for (int i=0; i<1000; i++) { x = myGen.nextInt( size ); // 0 thru size-1 y = myGen.nextInt( size ); width = myGen.nextInt( 101 ); // 0 thru 100 height = myGen.nextInt( 101 ); red = myGen.nextInt( 256 ); // 0 thru 255 green = myGen.nextInt( 256 ); blue = myGen.nextInt( 256 ); g.setColor( new Color( red, green, blue ) ); g.fillOval( x, y, width, height );

38. x = myGen.nextInt( size ); // 0 thru size-1 y = myGen.nextInt( size ); width = myGen.nextInt( 101 ); // 0 thru 100 height = myGen.nextInt( 101 ); red = myGen.nextInt( 256 ); // 0 thru 255 green = myGen.nextInt( 256 ); blue = myGen.nextInt( 256 ); g.setColor( new Color( red, green, blue ) ); g.fillRect( x, y, width, height );

39. x = myGen.nextInt( size ); // 0 thru size-1 y = myGen.nextInt( size ); height = myGen.nextInt( 101 ); g.setColor( Color.black ); g.fillRect( x, y, 4, height ); x = myGen.nextInt( size ); // 0 thru size-1 y = myGen.nextInt( size ); width = myGen.nextInt( 101 ); g.setColor( Color.black ); g.fillRect( x, y, width, 4); } // end for } // end paint