extending JPanel issue

[p.pavlov]

Hello,

I'm new to java and I'm having bit time trouble starting with Graphics class...

I have to do some custom graphics and other 2D figures. I decided to extend a basic component and just add the drawing features "on top", but hit a wall...
Okay so I use NetBeans7.0 and so far I
1) Created following class GraphicsPanel.

package gui;
import javax.swing.*; // For JPanel, etc.
import java.awt.*; // For Graphics, etc.


public class GraphicsPanel extends JPanel {
   private Graphics g1;    
    @Override
    public void paintComponent(Graphics g) {
        g1 = g;
        clear(g);
        g.drawLine (10, 0, 10, 100);
        g.drawLine (250, 100, 10, 100);
         

}
    public void AddLine() {
        g1.drawLine (100, 100, 10, 100);       
        super.paintComponent(g1);
        System.out.println("AddLine()");
    }
    // super.paintComponent clears off screen pixmap,
    // since we're using double buffering by default.
    protected void clear(Graphics g) {
    super.paintComponent(g);
    }
}

2) Added new JPanel to my applicaton's gui.
Since NetBeans doesn't allow modifications to variable declaration code, I used default

private javax.swing.JPanel TestGraphic;

but changed the initialization code to :

TestGraphic = new GraphicsPanel();

3) So now when I run the application I can see the result from
g.drawLine (10, 0, 10, 100); and g.drawLine (250, 100, 10, 100);
in public void paintComponent(Graphics g)

Picture - ImageShack® - Online Photo and Video Hosting

4) Now I'd like to have a method that enables me to add the actual content to this graphic using public void AddLine(), so I created the jButton with following code

       private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    GraphicsPanel myTestGraphic = (GraphicsPanel)TestGraphic; 
    myTestGraphic.AddLine();
    
    }

The method is called and System.out.println("AddLine()") is executed(I see result in console), but nothing happens in the graphical interface... I guess I shouldn't use g1 this way, but still can't figure out what should i do.

I've already spent half day on this and checked couple books and web tutorials, but still can't figure out what I'm missing... thank you..

Regards,
Pavel

[KevinWorkman]

No, you absolutely should not be using Graphics like that.

What you want to be doing is keeping a List of lines. In paintComponent(), just paint all the lines in the List. In the addLine() method, add a line to that List, then call repaint().

My best advice to you is to ditch the GUI builder altogether.

[p.pavlov]

Hello Kevin,

Thank you for the advice it was priceless!!
I solved the problem by doing following changes:

1) Defined line, because I couldn't find a predefined one.

public class Line {
    public int[] xy = new int[4];
    
    	public Line() {
		xy[0] = 0; //x1
                xy[1] = 0; //y1
		xy[2] = 0; //x2
                xy[3] = 0; //y2                
                
	}
        
    	public Line(int X1,int Y1,int X2,int Y2) {
		this.xy[0] = X1; this.xy[1] = Y1;
		this.xy[2] = X2; this.xy[3] = Y2;
	}   
        
}

2) Modified my GraphicsPanel

package gui;
import javax.swing.*; // For JPanel, etc.
import java.awt.*; // For Graphics, etc.


public class GraphicsPanel extends JPanel {

    int[] ln = new int[4];
    java.util.LinkedList<core.Line> ll = new java.util.LinkedList<core.Line>();
    
    public GraphicsPanel(){ 
        ll.add(new core.Line(10, 0, 10, 100));
        ll.add(new core.Line(10, 100, 400, 100));
    }

    @Override
    public void paintComponent(Graphics g) {
        // Clear off-screen bitmap
        super.paintComponent(g);   
        // Cast Graphics to Graphics2D
        Graphics2D g2d = (Graphics2D)g;      
        //print blue frame
        g2d.setPaint(Color.BLUE);
        for(int i = 0; i< 2; i++) {
            ln = ll.get(i).xy;
            g2d.drawLine(ln[0], ln[1], ln[2], ln[3]);
        }  
        // print red lines with the data 
        g2d.setPaint(Color.RED);
        for(int i = 2; i< ll.size(); i++) {
            ln = ll.get(i).xy;
            g2d.drawLine(ln[0], ln[1], ln[2], ln[3]);
        }            
    }    
 
    public void AddLine(core.Line l) {
        ll.add(l);        
        this.repaint();
    }

    public void AddLine(int x1, int y1, int x2, int y2) {
        ll.add(new core.Line(x1, y1, x2, y2));
        this.repaint();
    }    
}

3) Changed my JButton a little

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        GraphicsPanel myTestGraphic = (GraphicsPanel)TestGraphic; 
        myTestGraphic.AddLine(new core.Line(10, 100, 200, 50));
        myTestGraphic.AddLine(140, 100, 340, 50);
    
    }

Now I have
initial state - ImageShack® - Online Photo and Video Hosting
after jButton1 is clicked ImageShack® - Online Photo and Video Hosting

About dropping the GUI Builder... I already got warned that it's better to avoid it, but for a java-noob (especially coming from MS Visual Studio) doing GUI with text editor is a big cultural shock, I guess I'll need some time to agree to do that.. :D

Once again thanks for your response!
If I made big mistake again please do not hesitate to correct me:rolleyes:

Regards,
Pavel

[KevinWorkman]

Much better.

The only thing I'd like to point out is standard naming conventions- variables and methods should always start with a lower-case letter, classes start with a capital letter. It sounds picky, but it makes your code much easier to read.

Also, there already is a Line class in the standard API. Actually there are 3! Line2D (which is abstract), Line2D.Double, and Line2D.Float. You might use Line2D.Double instead of a custom Line class.