图形不显示（JAVA、GRAPHICS）

Question

I am building a pathway: a red cross in a white circle, and 3 green squares.

I have built the items but it does not show up. I have tried many things but I cannot figure our what I am missing... The graphics g is not showing up.

I tried to add getContentPane() and super.paint(g). I shall maybe add: .add(g) but I am not sure where...

Many thanks in advance for your help (and explanations so that I understand and avoid the mistake next time).

public class Robot0 extends JFrame implements ActionListener{


public Robot0(String nom, int larg, int haut){
JFrame fen = new JFrame(); // creer une fenetre, nommee fen, de la classe JFrame
fen.setTitle(nom); // definir un titre de fenetre
fen.setSize(larg, haut); // definir la taille de fenetre
fen.setLocationRelativeTo(null); // creer fen au centre de l’ecran
fen.setResizable(false); //prevent redimensionning
fen.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //Femer la fenetre (termine l’execution) quand on clique sur la croix rouge de fen
fen.setVisible(true); // rendre visible la fenetre fen
}    



Timer tm = new Timer(10,this);    


private int posX = 0; // (posX,posY) une position dans le panneau `a cr´eer
private int posY = 0;
private int velX = 1; 


public int getPosX() {
return posX;
}    
public void setPosX(int posX) {
this.posX = posX;
}
public int getPosY() {
return posY;
}
public void setPosY(int posY) {
this.posY = posY;
}

public void paint(Graphics g){
            super.paint(g);

            //Draw the pathway in a 800x600 pixels panel made up of 5 segments (using draw.Polyline)
            int xt[] = {50, 50, 250, 250, 350, 350};
            int yt[] = {50, 150, 150, 50, 50, 150};        
            g.drawPolyline(xt, yt, 6);  

            //On the pathway, draw 3 squares (the 3 rooms) 
            //J'ai place les carres tel que son centre soit sur la ligne de trajet
            g.setColor(Color.GREEN);    
            g.drawRect(35, 135, 30,30);
            g.drawRect(235, 35, 30,30);
            g.drawRect(335, 135, 30,30);

            //J'ai place le robot tel que son centre soit sur la ligne de trajet
            g.setColor(Color.WHITE);
            g.fillOval(40+posX,40+posY,20,20);

            g.setColor(Color.RED);
            g.drawLine(45+posX,50+posY,55+posX,50+posY);
            g.drawLine(50+posX,45+posY,50+posX,55+posY);

            tm.start();
    }


//ACTIONS TO BUILD //


// Build the Panel
public static void main(String[] args){
Robot0 r = new Robot0("Robot0", 800, 600);
r.getContentPane().setBackground(Color.BLUE);    
}

}

Answer 1

Robot0 extends JFrame , so is itself a JFrame . You therefore don't need to, and probably shouldn't, create a new JFrame in the constructor or Robot0 .

Replace

public Robot0(String nom, int larg, int haut){
JFrame fen = new JFrame(); // creer une fenetre, nommee fen, de la classe JFrame
fen.setTitle(nom); // definir un titre de fenetre
fen.setSize(larg, haut); // definir la taille de fenetre
fen.setLocationRelativeTo(null); // creer fen au centre de l’ecran
fen.setResizable(false); //prevent redimensionning
fen.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //Femer la fenetre (termine l’execution) quand on clique sur la croix rouge de fen
fen.setVisible(true); // rendre visible la fenetre fen
}  

with

public Robot0(String nom, int larg, int haut){
    setTitle(nom); // definir un titre de fenetre
    setSize(larg, haut); // definir la taille de fenetre
    setLocationRelativeTo(null); // creer fen au centre de l’ecran
    setResizable(false); //prevent redimensionning
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //Femer la fenetre (termine l’execution) quand on clique sur la croix rouge de fen
    setVisible(true); // rendre visible la fenetre fen
}