To draw circles on JPanel using JComboBox to determine number of them

[mneskovic]

I am making JApplet which has JPanel on it. I have JComboBox on JApplet (outside JPanel) and I should use it to select number of circles that will be drawn on JPanel. For example, if I choose 2, the JPanel should get 2 circles.

How can I access the paintComponent method inside JPanel and to "connect" it with JCombobox?

I have written the comboItemStateChanged method, but I don't know what to put in it. Here is how it looks:

 private void comboItemStateChanged(java.awt.event.ItemEvent evt) {
    int selection;
    selection = combo.getSelectedIndex();
    if (selection == 0) {
    }
    else if (selection == 1) {
    }
    else if (selection == 2) {
    }
      else if (selection == 3) {
    }
      else if (selection == 4) {
    }
}

Any ideas...?

[curmudgeon]

I think that you'll need a controller (the listener such as an item listener) that is outside of the two classes, the one holding the JComboBox and the one drawing the circles. Perhaps the class holding the JComboBox can have a public method called addItemListener(ItemListener il) and inside this method you add the parameter to the JComboBox as its ItemListener:

// warning: code neither tested nor compiled 
class ComboDisplayer {
  private JComboBox myComboBox = ....

  public void addItemListener(ItemListener il) {
    myComboBox.addItemListener(il);
  }

  //.... other code

}

Then similarly for the JPanel that does the painting allows the controller to change the number of circles by giving it a private int field, say circleCount, and a public method setCircleCount(int count), and within this method set the circleCount variable and tell the JPanel to repaint. Have this JPanel use the circleCount field to determine how many circles to draw:

// warning: code neither tested nor compiled 
class DrawCircles extends JPanel {
  private int circleCount = 0;

  public void setCircleCount(int circleCount) {
    this.circleCount = circleCount;
    repaint();
  }

  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    for (int i = 0; i < circleCount; i++) {
       // code for drawing circles
    }

  }
}

Then in the class that holds the two classes above, you create an ItemListener that listens for changes in the combobox and uses the changes to set the number of circles. Note that there will be no need for if blocks here since you'll simply be plugging the number obtained from the combobox into the circle drawing class.

[mneskovic]

Thank you very much :) Problem solved.