CODEWITHSUNDEEP
javaswingactionlistener
Sumeet
Sumeet

Reputation: 8292

Figure drawn without function call?

I am getting a problem in java program for moving a circle. The program has 2 basic buttons:

START: used for moving the circle

STOP: used for exiting the program

My problem is that the circle appears before I press the start button. However I make the call to move only when START Button is pressed which makes the call to repaint and then the circle should appear. But it appears by default. I have no problem in moving the circle. Here is my source code:

 import javax.swing.*;
 import java.awt.event.*;
 import java.awt.*;
 class Moving extends JFrame implements ActionListener
 {
   JButton start,stop;Move mypanel;

   Moving()
   {
    setTitle("Moving circle");
    setLayout(new BorderLayout());
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setSize(800,600);
    start=new JButton("START");
    stop=new JButton("STOP");
    start.addActionListener(this);stop.addActionListener(this);
    JPanel p=new JPanel();
    p.setLayout(new FlowLayout());
    p.add(start);p.add(stop);
    getContentPane().add(p,BorderLayout.SOUTH);
    mypanel=new Move();
    getContentPane().add(mypanel,BorderLayout.CENTER);

   }
   public void actionPerformed(ActionEvent e)
   {
    String s=e.getActionCommand();
    if(s.equals("STOP"))
            System.exit(0);
    else if(s.equals("START")) 
            mypanel.move();     
   }
   public static void main(String []args)
   {
    Moving obj=new Moving();
    obj.setVisible(true);
   }
 }

 class Move extends JPanel
 { static int x=80, cv=0;
  public void move()
  {     
    repaint();
  }
  public void paintComponent(Graphics g)
  {
    setBackground(Color.green);

    super.paintComponent(g);
    g.setColor(Color.red);
    if(x<500&&cv==0)
        {g.fillOval(x, 80, 100, 100);this.inc();}
    else if((x>=500||cv==1)&&x>=80)
    {
     cv=1;g.fillOval(x, 80, 100, 100);this.dec();
    }
    else cv=0;      
  }
  public void inc()
  {
    x+=10;
  }
  public void dec()
  {
    x-=10;
  }
 }

Upvotes: 1

Views: 50

Answers (2)

Blip
Blip

Reputation: 3171

My suggestion is that if you do not want to show your circle before the pressing of the start button you have to remove drawing of the circle from the paintComponent method.

You can achieve the above by declaring a new method in your Move class say drawCircle like this:

public void drawCircle(Graphics g){
    g.setColor(Color.red);
    if(x<500&&cv==0)
        {g.fillOval(x, 80, 100, 100);this.inc();}
    else if((x>=500||cv==1)&&x>=80)
    {
     cv=1;g.fillOval(x, 80, 100, 100);this.dec();
    }
    else cv=0;      
}

now in your Move class introduce a new boolean variable say circleShowing and intialise to false. This is declared so that the paintComponent method of the Move class can decide whether the circle should be drawn or not. You can do it like this:

  public void paintComponent(Graphics g){
    setBackground(Color.green);
    super.paintComponent(g);
    if(circleShowing){
       drawCircle(g);
    }
  }

Now finally in the actionPerformed method of your Moving class you in the else if block you could write the following:

mypanel.circleShowing = true;
mypanel.move();

I hope if you make these changes this will work as you wish.

Upvotes: 0

Parth Soni
Parth Soni

Reputation: 11648

By default setVisible would be true. So, if you don't won't to show panel on load then make it false on constructor.

And then make it visible when you hit Start.

See below:

class Move extends JPanel {
    static int x = 80, cv = 0;

    Move(){
        setVisible(false); <-- Make it false here
    }

    public void move() {
        this.setVisible(true);     <----- make it visible here when you click start
        repaint();
    }

    public void paintComponent(Graphics g) {
        setBackground(Color.green);
         ..... REMAINING CODE
    }
}

Upvotes: 1

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