How can I draw lines, rectangles, and circles in my Java paint program?

Question

I'm working on a paint program for one of my classes and I'm stuck. This is a part of my code (separated into 3 Java classes). When I click on the button "Ligne", I want to be able to draw a line in the white rectangle. Sorry for the French comments.

---

//cree une fenetre    
public class QUESTION  
{  
    public static void main(String[] args)  
    {  
        Paint_GUI test2 = new Paint_GUI();  
    }  
} 

---

import java.awt.*;  
import javax.swing.*;  

//class contenant le code pour dessiner  
public class Paint_Dessin extends JPanel
{  
   public void paintComponent(Graphics g)  
   {  
      super.paintComponent(g);  
     setBackground(Color.white);  
     g.setColor(Color.black);  
   }  

  public void TracerLigne()  
  {  
     System.out.println("LIGNE");  
  }  
}   

---

import javax.swing.*;  
import java.awt.event.*;  
import java.awt.*;  

public class Paint_GUI extends JFrame  
{  
    //Panels contenant tout les bouton de mon interface  
    private JPanel panelBtn;  

    //Bar d'outil Btn  
    private JButton BtnTracerLigne;

    //object Paint_Dessin 
    private Paint_Dessin espaceDessin = new Paint_Dessin();


    public Paint_GUI()  
    {  
        final int WINDOW_WIDTH = 650;  
        final int WINDOW_HEIGHT = 450;  

        setSize (WINDOW_WIDTH, WINDOW_HEIGHT);  
        setTitle("Paint v.2.0");  
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
        setLayout(new BorderLayout());  

        // Appeler la methode qui construit la barre de BTN.  
        buildPanelBtn();  
        add(panelBtn, BorderLayout.NORTH);    
        add(espaceDessin, BorderLayout.CENTER);  

        // Afficher la fenetre.  
       setVisible(true);  
 }  

 private void buildPanelBtn()  
 {  
     BtnTracerLigne = new JButton("Ligne");  
     BtnTracerLigne.addActionListener(new LigneListener());  

     // Creer le panel.  
     panelBtn = new JPanel();  
     // Ajouter les composantes au label  
     panelBtn.add(BtnTracerLigne);  
}  
private class LigneListener implements ActionListener  
{  
   public void actionPerformed(ActionEvent e)  
   {    
    espaceDessin.TracerLigne();  
   }  
}  

---

Answer 1

you should create another class like GraphComponent for instance, that extends JComponent. You should also look at implementing MouseInputListener. I will not give you the solution, but it'a a good start ;).

Anyway, I see you're french so take a look at site-du-zero, it's full of very good tutorials (in french).

N.B: You shouldn't name you classes like QUESTION, put Question instead

EDIT : here another hints :

public class Paint_Dessin extends JComponent implements MouseInputListener{  
    private List<Point> startPoints = new ArrayList<Point>();
    @Override
    public void mouseClicked(MouseEvent e) {
        int x = e.getX();
        int y = e.getY();
        Point p = new Point(x,y);
        startPoints.add(p);
        repaint();
    }
    protected void paintComponent(Graphics g) {
        g.setColor(getForeground());
        Graphics2D g2 = (Graphics2D) g;
        for (Point p : startPoints)
            p.draw(g2);
    }
    public class Point{
        private int x,y;
        public Point(int x, int y){
            this.x = x;
            this.y = y;
        }
        void draw(Graphics2D g2) {
            //do the drawing with the right shape you want 
        }
    }

and see Shape. You should implements others method from the MouseInputListener, like mouseDragged,....

Answer 2

You're current code has a problem in that you're creating a new Paint_Dessin in the LigneListener class's actionPerformed method, and while this object is created from the same class as the Paint_Dessin object that is displayed in the JFrame, it is a completely different object and calling methods on it will have absolutely no effect on the Paint_Dessin that is displayed. What you need to do is to declare a private Paint_Dessin variable once in the Paint_GUI class, a class field, initialize this variable either at its declaration or in the Paint_GUI constructor, and then display this object in the GUI and also call methods on this GUI in the listener class. e.g.,

public class Paint_GUI extends JFrame  
{  
    private JPanel panelBtn;  
    private JButton BtnTracerLigne;  
    private Paint_Dessin espaceDessin = new Paint_Dessin();

    public Paint_GUI()  
    {  
        final int WINDOW_WIDTH = 650;  
        //... code deleted for sake of brevity

        // Paint_Dessin espaceDessin = new Paint_Dessin();  
        add(espaceDessin, BorderLayout.CENTER);  

        // Afficher la fenetre.  
       setVisible(true);  
 }  

 private void buildPanelBtn()  
 {  
     // ....
 }  

private class LigneListener implements ActionListener  
{  
   public void actionPerformed(ActionEvent e)  
   {  
    // Paint_Dessin tracerLigne = new Paint_Dessin();  
    // tracerLigne.TracerLigne();  
    espaceDessin.TracerLigne(); // call the method on the same object!
   }  
}