Draw in another component

Question

I have a homework to do but there is not enough information and I'm stuck right now... Here is the issue, I have three classes :

"ChoicePanel" extends JPanel and add buttons to select a color with a JComboBox

public class ChoicePanel extends JPanel{

    Draw dessin;

    public ChoicePanel(Draw df) {
        dessin = df;
        ...
        // couleurs
        final JComboBox<String> couleurs = new JComboBox<>(new String[] {"bleu", "jaune", "rouge"});
        add(couleurs);
    }

    /** Know what color is selected */
    private Color determineCouleur(int indice){
        switch (indice) {
        case 0:
            return Color.BLUE;
        case 1:
            return Color.YELLOW;
        case 2:
            return Color.RED;
        default:
            return Color.BLACK;
        }
    }
}

"Draw" extends JPanel and stock all outline and paint them
"Main" create the frame with those classes included

I have to set Draw as a MouseMotionListener but i can't get the color selected in ChoixePanel because the JComobox is created in the construcor and I can't set it to a field. So how can I check ChoicePanel's buttons values from Draw ?

Every answer will be very helpfull !

You are passing `Draw` to `ChoicePanel` and holding it as a field. That field already has access to `ChoicePanel`'s variable's. — user1803551, May 16 '15 at 11:43
Also, when posting a HW question, it's a good idea to tell what you can change in the code and what not, and if there are classes you are not allowed to use. — user1803551, May 16 '15 at 11:44
I didn't know that, so how can I get "couleurs" var from Draw ? For the second comment : I can't add fields like Color in Draw. Also, determinerCouleur have to stay private — oktomus, May 16 '15 at 12:39
`couleurs` is in `ChoicePanel`, you don't get it "*from Draw*". Maybe post the relevant parts of `Draw`. — user1803551, May 16 '15 at 12:54
@user1803551, the MouseMotionListener is Draw so in Draw in MouseDragged, how can i get the color ? — oktomus, May 16 '15 at 15:18

score 1 · Accepted Answer · edited May 23 '17 at 11:51

The goal of the exercise may be to help you learn about scope and access in Java. Let's refactor the example seen here to meet your requirements.

A ChoicePanel needs a way to update an instance of the Draw panel; you can pass a reference as a parameter to the panel's constructor or the factory method shown below.
```
public static JPanel create(Draw draw) {…}
```
In the combo's action listener set the color on draw; optionally invoke draw.repaint() if the change is not to a bound property such as background color.
```
Hue h = (Hue) colors.getSelectedItem();
draw.setBackground(h.getColor());
//draw.repaint();
```
Because Draw may contain no components, override getPreferredSize() as shown here and below.
I can't create a private class…

For convenience in running the example below, ChoicePanel and Draw are included as private static members. Simply move each to its own file, absent the modifiers, to get stand-alone classes having package-private access from Main.
```
JFrame f = new JFrame("Main");
Draw d = new Draw();
f.add(d, BorderLayout.CENTER);
f.add(ChoicePanel.create(d), BorderLayout.SOUTH);
```

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;

/**
 * @see https://stackoverflow.com/a/5663782/230513
 */
public class Main {

    private static class ChoicePanel {

        public static JPanel create(Draw draw) {
            JPanel p = new JPanel();
            final JComboBox colors = new JComboBox();
            for (Hue h : Hue.values()) {
                colors.addItem(h);
            }
            colors.addActionListener((ActionEvent e) -> {
                Hue h = (Hue) colors.getSelectedItem();
                draw.setBackground(h.getColor());
            });
            p.add(colors);
            return p;
        }
    }

    private static class Draw extends JPanel {

        public Draw() {
            this.setBackground(Hue.values()[0].getColor());
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(320, 240);
        }
    }

    public enum Hue {

        Cyan(Color.cyan), Magenta(Color.magenta), Yellow(Color.yellow),
        Red(Color.red), Green(Color.green), Blue(Color.blue);

        private final Color color;

        private Hue(Color color) {
            this.color = color;
        }

        public Color getColor() {
            return color;
        }
    }

    private void display() {
        JFrame f = new JFrame("Main");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Draw d = new Draw();
        f.add(d, BorderLayout.CENTER);
        f.add(ChoicePanel.create(d), BorderLayout.SOUTH);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> {
            new Main().display();
        });
    }
}

Thank you @trahgod, i'm going to try this :) – oktomus May 16 '15 at 17:32 — oktomus, May 16 '15 at 17:32

Draw in another component

1 Answers1