ming 3 Resize the Size to [700, 500]. Note that the background containers in the program code: reference the then under () { 153, 255, 0 ) );

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1 ECCS 166 Programm ming 3 Dr. Estell Spring Quarter Laboratory Assignmen nt 7 Graphics and Polymorphism 15 April The purpose of the next few laboratory assignments is to create a simple drawing program that will expose you both to the "power of polymorphism" and to the basic features of Java graphics. 2. Launch NetBeans and create a new Java application project entitled SketchPad, following the normal procedure for the creation of a new project as outlined in thee NetBeans Cheat Sheet on the course web site. Name the JFrame form SketchPad so that the source code file for this project is SketchPad.java. Use "foo" as the package name. In its properties, please givee the JFrame the title SketchPad. Resize the frame so thatt it is at least 700 pixels wide by at least 500 pixels high by going into the "Code" page of the "Properties" for the JFrame, select "Generate Resize Code" for the Form Size Policy, then set the Form Size to [700, 500]. 3. Modify the constructor method in SketchPad to read as follows: public SketchPad( () { initcomponents(); getcontentpane().setbackground( new java.awt.color( 153, 255, 0 ) ); Note that the background color of the application is no longer gray. Briefly, there are three top-level container has a contentt pane that, generally speaking, contains the visible components in that top-level container's GUI. In order to render images and components onto the top-level container, the program normally makes a reference to the container's content pane through a call to getcontentpane(). The problem with setting the background iss that NetBeans is not referencing the JFrame's content pane. Accordingly, when NetBeans generates the code: containers in Java GUI programs: JFrame, JApplet, and JDialog. Each top-levell jframe.setbackground( Color.black ); you do not see the effect of changingg the background color, except when the program starts and whenever itt is resized. Then you willl see the black frame behind the content pane only briefly. You must explicitly reference the JFrame's content pane, via getcontentpane().setbackground( Color.BLACK ) instead to get a permanent black background. Similarly, use the content pane for the setforeground and setfont methods. 4. Go up to the menu bar and select File New File. Under 'Categories:' select "Java GUI Forms," then under 'FileTypes:' select 'JPanel Form'. Click on the 'Next' button.

2 5. In the 'New JPanel Form' dialog box, set the class name to 'SketchPanel' and the package to 'foo'. 6. You should now see the design view for the file 'SketchPanel.java'. The properties of this class are inherited from the JPanel class; it can be treated as a customized panel. Resize the panel such that it is 400 pixels wide by 400 pixels high by setting the maximumsize, minimumsize, and preferredsize property fields to [400, 400]. In addition, set the background color of the panel to white. 7. Compile the code for SketchPanel (Build Compile SketchPanel.java" or use the F9 key). 8. Right click on the SketchPanel.java entry in the Projects tab, and select Tools Add to Palette In the "Select Palette Category" dialog box, click on "Beans" then click OK. In your Palette of components shown to the right of the IDE, underneath "Beans" you'll now see "SketchPanel". Click and drag an instance of the SketchPanel onto the upper left corner of your SketchPad GUI; name this component 'mysketchpanel'. 9. Go to the source view for SketchPanel.java and do the following: a. add the import statements: import java.util.*; import javax.swing.*; import java.awt.*; b. add the instance variables for the class: private java.util.list itemstodraw = new ArrayList(); c. modify the constructor to read as follows: public SketchPanel() { initcomponents(); this.setcursor( new Cursor( Cursor.CROSSHAIR_CURSOR ) ); d. add the following method for rendering images: public void paintcomponent( Graphics g ) { super.paintcomponent( g ); g.setcolor( Color.BLACK ); Iterator thispoint = itemstodraw.iterator(); Point last = null; while ( thispoint.hasnext() ) { Point p = (Point) thispoint.next(); if ( last!= null ) g.drawline( last.x, last.y, p.x, p.y ); last = p; 10. Switch to the design view for SketchPanel and add the following code for when a mouse dragged event occurs on the panel: Point p = new Point( evt.getx(), evt.gety() ); itemstodraw.add( p ); repaint(); 11. Compile SketchPanel.java 12. Run the project and perform various mouse dragged operations in the panel; what do you observe? Record your observations on the "lab performance" sheet. 13. At this time, demonstrate your application to the lab instructor or TA and have your "lab performance" sheet initialed for this section.

3 14. We currently have an application that will allow us to perform a very primitive form of freehand sketching. Currently, the SketchPanel class draws by storing Point objects between which we draw lines. We like too have greater flexibility in what we are able to draw through the employment of polymorphic behavior. What we will do is createe an abstractt class that defines the general operations pertinent to the rendering of a drawn image, then createe concrete subclasses that provide the implementation details for the actual rendering of a particular image. 15. Let's start by the creation of a DrawItem abstractt class. Thiss class will have two instance variables: itemlocation this variable is of type Point. It is used to store the x-y coordinate of a mouse event. itemcolor this variable is of type Color and storess the color that is to be used to draw the item. Please note that you willl need to import classes from the java.awt package; specifically, java. awt.color,, java.awt.graphics, and java.awt.point. Appropriate get/set methods for the instance variables and a constructor method are also required: getitemlocation setitemlocation getitemcolor setitemcolor DrawItem( Point thislocation, Color thiscolor ) Additionally, we have two abstract methods: public abstract void draw( Graphics g ) this method iss passed a reference to a Graphics object upon which the item is to be rendered. public abstract void add( Point p )- this method is passed a Point object for where something "just happened" with respect to the item being drawn. At this time, please write the DrawItem class by going up to the menu bar and select File New File. Underr 'Categories:' select "Javaa Classes," then under 'FileTypes:' select 'Java Class'. Click on 'Next'.

4 In the subsequent 'New Java Class' dialog box, use 'DrawItem' as the name of the new class. Once you have finished entering the code for DrawItem, compile it to verify its syntactical correctness. 16. At this time, show your compiled code for DrawItem to the lab instructor or TA and have your "lab performance" sheet initialed for this section. 17. Add the following import statementss to SketchPad.java: import java..awt.*; import javax.swing.*;

5 18. We now need to create the class Freehand that is an extension of DrawItem. Freehand will give us the same functionality as we had when drawing in the previous laboratory, plus the addition of color. So why the fuss? By using an abstract class, we can employ polymorphism to specify what happens when data is "added" to an object we're currently working with and how that object is to be rendered, without having to perform major code modifications. Since the technique is a bit involved (but the code isn't long), please create a new file called Freehand.java and enter the following code (or copy it from the SketchPad Code folder within the Programming 3 Resources Dropbox folder): /* * Freehand.java * John K. Estell * Created on April 15, 2006, 11:49 AM * * To change this template, choose Tools Template Manager * and open the template in the editor. */ package foo; import java.awt.*; import java.util.*; /** * estell */ public class Freehand extends DrawItem { private java.util.list dots = new ArrayList(); // list of connect-the-dots (i.e. points) public Freehand( Point thispoint, Color thiscolor ) { super( thispoint, thiscolor ); // superclass has location and color instance variables dots.add( thispoint ); // location is also the first point in the list public void add( Point thispoint ) { dots.add( thispoint ); // adds a point to the end of the connect-the-dots list public void draw( Graphics g ) { Iterator setofpoints = dots.iterator(); Point lastpoint = null; // needed as for n points there are n-1 lines to draw while ( setofpoints.hasnext() ) { Point thispoint = (Point) setofpoints.next(); if ( lastpoint!= null ) { g.drawline(lastpoint.x, lastpoint.y, thispoint.x, thispoint.y); lastpoint = thispoint; // update where the current last point is 19. In the source view for SketchPanel, add pencolor as an instance variable to the class, with the default color set to black (i.e use Color.BLACK). Next, add the method void setpencolor( Color thiscolor ).

6 20. In the design view for SketchPad, place a button on the lower left portion of the applet for pen color selection with the label reading "Set pen color ". Name the component 'setpencolorbutton'. Set the "focus painted" property for this button to false. Give the button an appropriate tool tip text message. Set an interaction where the actionperformed method associated with this button invokes Swing's color chooser dialog as follows: private void setpencolorbuttonactionperformed(java.awt.event.actionevent evt) { Color selectedcolor = JColorChooser.showDialog( mysketchpanel, "Choose pen color", Color.BLACK ); if ( selectedcolor!= null ) mysketchpanel.setpencolor( selectedcolor ); 21. In the design view for SketchPanel, add a mousepressed event where the to do code is as follows: private void formmousepressed(java.awt.event.mouseevent evt) { itemstodraw.add( new Freehand( evt.getpoint(), pencolor ) ); 22. While in the source view for SketchPanel, modify the paintcomponent method to read as follows: public void paintcomponent( Graphics g ) { super.paintcomponent( g ); Iterator setofitems = itemstodraw.iterator(); while ( setofitems.hasnext() ) { DrawItem thisitem = (DrawItem) setofitems.next(); // get the item g.setcolor( thisitem.getitemcolor() ); // set the pen color to draw thisitem.draw( g ); // use polymorphism to render it 23. Modify the formmousedragged method in SketchPanel to read as follows: private void formmousedragged(java.awt.event.mouseevent evt) { DrawItem currentitem = (DrawItem) itemstodraw.get( itemstodraw.size() - 1 ); currentitem.add( evt.getpoint() ); repaint(); 24. In the source view for SketchPanel, add the method void clear() for the purpose of erasing all drawn items from the panel; its implementation invokes the clear() method of the itemstodraw list. Next, place a button on the SketchPad application called "clearscreenbutton" that invokes the clear() method of the instantiated SketchPanel object, followed by invoking repaint(). 25. At this time, build your application, then demonstrate your application to the lab instructor or TA by drawing freehand images in various colors. Have your "lab performance" sheet initialed for this section and turn it in to Dr. Estell. Please keep the SketchPad project handy, as we will continue to work on it in lab next week.