CODEWITHSUNDEEP
java
hkguile
hkguile

Reputation: 4359

java paint () auto executed?

import java.awt.*;
import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.event.*;
import java.awt.geom.*;
import java.util.*;

public class test extends JFrame implements ActionListener, MouseListener {

    private Vector<String> vlist = new Vector<String> ();
    private int mouseX, mouseY;
    Canvas c = new Canvas();

    public test () {
        setSize(400,400);
        addMouseListener(this);

    }

    public static void main(String[] args) {


        java.awt.EventQueue.invokeLater(new Runnable() {
              public void run() {
                    test frame = new test();
                    //frame.setBackground(Color.yellow); 
                    frame.setVisible(true);
              }
        });
    }

    public void actionPerformed(ActionEvent ae) {

    }

    @Override
    public void paint(Graphics g) {

        Shape circle = new Ellipse2D.Float(100f, 100f, 100f, 100f);
        Graphics2D ga = (Graphics2D)g;
        ga.draw(circle);

    }

    public void move() {

    }

    public void drawCircle(int x, int y) {

    }

    public void mouseClicked(MouseEvent e) {
        repaint();

    }

    public void mouseExited(MouseEvent e) {

    }

    public void mousePressed(MouseEvent e) {
        this.mouseX=e.getX();
        this.mouseY=e.getY();
    }

    public void mouseReleased(MouseEvent e) {

    }

    public void mouseEntered(MouseEvent e) {

    }
}

i want to write a testing program to learn the graphic programming in java. To run the above code, the circle is automatically drawn. Why the paint() method is auto executed? I the circle to be created when i clicked the mouse.

Upvotes: 0

Views: 1799

Answers (3)

wannik
wannik

Reputation: 12706

Add an attribute to the class.

boolean draw;

Surround the code in the paint(...) with 

if (draw) {
    // existing code
}

This will make the program draws only when draw is true. Initially, it is false so it won't draw anything. The value attribute draw will be true when the mouse is clicked.

public void mouseClicked(MouseEvent e) {
    draw = true;
    repaint();
}

Upvotes: 1

Hovercraft Full Of Eels
Hovercraft Full Of Eels

Reputation: 285403

The Swing paint manager calls the paint method when the JFrame is rendered. For more details on the inner workings of this, please see Painting in AWT and Swing.

To improve your program, you'll want to

  • Do your drawing in a JPanel or other component that inherits from JComponent.
  • Do the actual painting in the JPanel's paintComponent method, not the paint method.
  • Call the super.paintComponent() method first.
  • If you want to paint the circle on mouse click then add an if block in the paintComponent method to only draw the circle if some class field boolean is true -- and then set it true in your MouseListener and then call repaint.
  • Most importantly, read tutorials on how to do Swing graphics as much of it is somewhat counter-intuitive (as evidenced by Tom's answer in this thread).

Upvotes: 1

camickr
camickr

Reputation: 324118

You should NOT be overriding the paint() method of the JFrame to do custom painting.

You should override the paintComponent() method of a JPanel or JComponent and add that component to the JFrame.

Check out the Swing tutoria on Custom Painting for the basics.

Check out Painting in AWT and Swing for detailed information.

Upvotes: 0

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