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9.2

Java Applet to display shapes

Asked by HRMorton in Java Programming Language

Hi,
I have a Java Applet that display's 2 buttons, if 1st is pressed an additional box is displayed for input of a value. From this a circle is drawn. If the other button is pressed 2 additional boxes are shown for input and from this a rectangle is drawn.

I have 2 problems with it, if I press the button nothing happens until I re-size the applet then the buttons are shown. Almost like it's waiting for something to happen before showing them.

If I draw the circle, then press the second button I get errors :-
Exception in thread "AWT-EventQueue-1" java.lang.NumberFormatException: For input string: ""
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
at java.lang.Integer.parseInt(Integer.java:468)
at java.lang.Integer.valueOf(Integer.java:553)
at Assignment2.pkgshapes.paint(pkgshapes.java:160)
at sun.awt.RepaintArea.paintComponent(RepaintArea.java:248)
at sun.awt.RepaintArea.paint(RepaintArea.java:224)
at sun.awt.windows.WComponentPeer.handleEvent(WComponentPeer.java:301)
at java.awt.Component.dispatchEventImpl(Component.java:4486)
at java.awt.Container.dispatchEventImpl(Container.java:2116)
at java.awt.Component.dispatchEvent(Component.java:4240)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

I've tried re-setting the string that will hold the input but nothing seems to be working.
Any help with these problems would be greatly appreciated.

Thanks
Heather

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             package Assignment2;
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
public class pkgshapes extends java.applet.Applet implements ActionListener
{
    // Define Labels, Text Fields and Buttons to be used in Applet
    Label displayLabel, enterLabel, radiusLabel, lengthLabel, heightLabel ;
    Label areaCircleLabel, circumCircleLabel;
    TextField displayBox, enterBox, radiusBox, lengthBox, heightBox ;
    TextField areaCircleBox, circumCircleBox;
 
    Button drawCircle = new Button("Draw A Circle");
    Button drawRectangle = new Button("Draw A Rectangle");
    Button calculate = new Button("Calculate");
 
    // Define String's used to determine which button pressed
    String isCircle="N", isRectangle="N", isCal = "N", calCircle = "N", calRectangle = "N";
 
    String inputString;
 
    // Define variables to hold radius, length and height values
    // Define variables to hold caluclated values
    int radius, length, height, areaRectangle, premRectangle;
    double areaCircle, circumCircle;
    final double pi = 3.14;
 
/************************************************************************/
/**  Initialisation Function                                           **/
/************************************************************************/
    public void init() {
 
        // Add circle button with action listener
        add(drawCircle);
	drawCircle.addActionListener(this);
 
        // Add Rectangle button with action listener
        add(drawRectangle);
	drawRectangle.addActionListener(this);
 
        // Add Label for Radius Text Box
        enterLabel = new Label ( "Enter Radius" ) ;
        enterBox = new TextField (12 ) ;
 
        radiusLabel = new Label ( "Enter Radius of Circle" ) ;
        radiusLabel.setVisible(false);
        add ( radiusLabel ) ;
        
        radiusBox = new TextField ( 12 ) ;
        // Hide radius box
        radiusBox.setVisible(false);
        add ( radiusBox ) ;
        
        lengthLabel = new Label ( "Enter Length of Rectangle" ) ;
        lengthLabel.setVisible(false);
        add ( lengthLabel ) ;
 
        lengthBox = new TextField ( 12 ) ;
        lengthBox.setVisible(false);
        add ( lengthBox ) ;
 
        heightLabel = new Label ( "Enter Height of Rectangle" ) ;
        heightLabel.setVisible(false);
        add ( heightLabel ) ;
 
        heightBox = new TextField ( 12 ) ;
        heightBox.setVisible(false);
        add ( heightBox ) ;
 
        calculate.setVisible(false);
        add(calculate);
        calculate.addActionListener(this);
    }
    
/************************************************************************/
/**  Paint Function                                                    **/
/************************************************************************/
    public void paint(Graphics gscreen)
	{
                inputString = "";
                // Circle Button Pressed, display box to accept radius
                if( isCircle== "Y" ){
                    isCircle = "N";
                    calCircle = "Y";
 
                    // Display box to accept radius
                    radiusBox.setText ( "" ) ;
                    radiusLabel.setVisible(true);
                    radiusBox.setVisible(true);
                    radiusBox.requestFocus();
 
                    // Hide Length and height boxes 
                    lengthLabel.setVisible(false);
                    lengthBox.setVisible(false);
 
                    heightLabel.setVisible(false);
                    heightBox.setVisible(false);
 
                    // Display Calculate Button
                    calculate.setVisible(true);
                    
                    // Re-set value of Calculate Circle
                    calRectangle = "N";
 
                }
		else if (isRectangle == "Y"){
                    
                    lengthBox.setText ( "" ) ;
                    lengthLabel.setVisible(true);
                    lengthBox.setVisible(true);
 
                    heightBox.setText ( "" ) ;
                    heightLabel.setVisible(true);
                    heightBox.setVisible(true);
 
                    radiusLabel.setVisible(false);
                    radiusBox.setVisible(false);
 
                    lengthBox.requestFocus();
 
                    isRectangle = "N";
                    calRectangle = "Y";
                    // Re-set value of Calculate Circle
                    calCircle = "N";
                    calculate.setVisible(true);
                    }
                // Calculate Button Pressed
                else if (isCal == "Y" ){
 
                    // Calculate Dimensions and Draw a Circle
                    if (calCircle == "Y" ){
 
                        inputString = radiusBox.getText() ;
                        radius = Integer.valueOf( inputString ).intValue();
 
                        // Calculate the area of the Circle 3.14 * radius * radius
                        areaCircle = radius * radius * pi;
                        circumCircle = (radius * 2) * pi;
 
                        gscreen.drawString("Area of the Circle is " + areaCircle,80, radius + 130);
                        gscreen.drawString("Circumference of the Circle is " + circumCircle,80,radius + 150);
 
                        // Draw Circle with parameter given
        		gscreen.setColor(Color.red);
                        gscreen.drawOval(85,105,radius,radius);
                    }
                    // Calculate Dimensions and Draw a Rectangle
                    if (calRectangle == "Y" ){
                        inputString = lengthBox.getText() ;
                        length = Integer.valueOf( inputString ).intValue();
 
                        inputString = heightBox.getText() ;
                        height = Integer.valueOf( inputString ).intValue();
 
                        // Calculate the area of the Rectangle length * breadth
                        areaRectangle = length * height;
                        premRectangle = 2 * ( length * height );
 
                        gscreen.drawString("Area of the Rectangle is " + areaRectangle,80, height + 120);
                        gscreen.drawString("Perimeter of the Rectangle is " + premRectangle,80,height + 130);
 
                        // Draw Rectangle with length and Height given
        		gscreen.setColor(Color.red);
                        gscreen.fillRect(85, 105, length,height);                    
                        }
                    }
                } 
/************************************************************************/
/**  Actioned Performed Function                                       **/
/************************************************************************/
    public void actionPerformed ( ActionEvent event )
    {
        // Deal with the button click event Find out which Button generated the event
        String arg = event.getActionCommand() ;
        if ( arg.equals( "Clear" ) ){
            // Re-set Boxes when clear button selected
            }
        // Clear not selected, Check if Pound or Euro selected
        else
        {
            try
            {
                //  Draw Circle button pressed
		if (event.getSource()==drawCircle){
                    isCircle = "Y";
                    isRectangle = "N";
                    repaint();
                    }
                //  Draw Rectangle button pressed
                if (event.getSource()==drawRectangle){
                    isCircle = "N";
                    isRectangle = "Y";
   		    repaint();
                    }
                //  Caluclate button pressed
		if (event.getSource() == calculate){
                    isCal = "Y";
   		    repaint();
                }
            }
            /**********************************************************************/
            /**  Value entered by user was not an integer                        **/
            /**********************************************************************/
            catch ( NumberFormatException entry ){
                showStatus ( "Error: Invalid Input - please enter a valid number" ) ;
                }
       }                 
    }
    
}

           
         

Keywords: Java Applet to display shapes

	Title
1	Applet Editor
2	PixelGrabber with AWT + Antialiasing
3	How does this double buffering code …
4	problem with rotating..
5	Graphics application in Java

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Java Applet to display shapes

Asked by HRMorton in Java Programming Language

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