java applet中的paint（）被无故两次调用

Question

Is there a common reason why the paint() method may be called twice without being intended. I have the following code:

public void paint(Graphics g)
{
     //Graphics2D gg;
     //gg=(Graphics2D) g;

     drawMatrix(g);

}

        private void drawMatrix(Graphics g) {

       int side = 40;
       hex hexagon=new hex();
       for(int i = 0; i<9; i++) 
          for(int k = 0; k<9; k++){ 

            g.setColor(Color.lightGray);
            g.fill3DRect(i*side,k*side, side, side, true);
            if (matrix[i][k]!=null){System.out.println("i is "+i+" k is "+k);
                g.setColor(Color.black);hexagon.DrawHexfromMatrix(g, i, k, Color.black);}
    }   
    }

hex is a class that extends polygon (to model a hexagon figure), and the DrawHexfromMatrix is a function that draws a hexagon from the index of the matrix that is drawn(put the hexagon in the slot of a matrix). I can provide the whole code if you think it helps, but for now i don't understand why the system.out.println is executed twice.( for example if[1][2] and [2][3] are not null it will print:

    i is 1 k is 2 
    i is 2 k is 3 
    i is 1 k is 2
    i is 2 k is 3  

I think this also affects my drawing because sometimes although an element exists at [i][k] is isn't drawn.(matrix is a matrix of hex).

Later edit: Is it possible somehow that g.fill3DRect(i*side,k*side, side, side, true); to overpaint the hexagons i'm trying to paint with hexagon.DrawHexfromMatrix(g, i, k, Color.black);???

Answer 1

First of all, you should not paint directly to a JApplet .

You should define a JPanel that is added to the JApplet . You paint to the JPanel .

Second, you should use the paintComponent() method, and call the super class behavior, like this.

protected void paintComponent(Graphics g) {
    // Paint the default look.
    super.paintComponent(g);

    // Your custom painting here.
    g.drawImage(foregroundImage, x, y, this);
}

Third, you have no control over when Swing fires the paintComponent() method. You should do the calculations in some other method, and limit the code in paintComponent() to actual drawing methods.