I would like to create a JPanel and draw things on it one by one. I would like to see them added after each other. The problem is, I always have to wait until everything is finished by paintComponent method. Is there a way to achieve what I desire? Thanks in advance!
package javapaintui;
import java.awt.*;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.*;
class JavaPaintUI extends JFrame {
private JPanel jPanel2;
public JavaPaintUI() {
initComponents();
}
private void initComponents() {
jPanel2 = new Panel2();
this.setContentPane(jPanel2);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
pack();
}
class Panel2 extends JPanel {
Panel2() {
setPreferredSize(new Dimension(420, 420));
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawString("BLAH", 20, 20);
try {
Thread.sleep(5000);
} catch (InterruptedException ex) {
Logger.getLogger(JavaPaintUI.class.getName()).log(Level.SEVERE, null, ex);
}
g.drawRect(200, 200, 200, 200);
}
}
public static void main(String args[]) {
EventQueue.invokeLater(new Runnable() {
public void run() {
new JavaPaintUI().setVisible(true);
}
});
}
}
Never, ever, ever use Thread.sleep(...) in a Swing application's event dispatch thread. That goes 100-fold true for the paintComponent method as you put it to sleep. The solution is to use a Swing Timer.
e.g.,
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.RenderingHints;
import java.awt.Shape;
import java.awt.Stroke;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import javax.swing.*;
class JavaPaintUI extends JFrame {
private static final Color FILL_COLOR = Color.BLUE;
private static final Color BORDER_COLOR = Color.RED;
public static final Stroke STROKE = new BasicStroke(4f);
private JPanel jPanel2;
public JavaPaintUI() {
initComponents();
}
private void initComponents() {
jPanel2 = new Panel2();
this.setContentPane(jPanel2);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
pack();
}
class Panel2 extends JPanel {
private static final int TIMER_DELAY = 2000;
private Random random = new Random();
private List<Shape> shapeList = new ArrayList<>();
Panel2() {
setPreferredSize(new Dimension(420, 420));
new Timer(TIMER_DELAY, new ActionListener() {
@Override
public void actionPerformed(ActionEvent evt) {
int width = random.nextInt(100);
int height = random.nextInt(100);
int x = random.nextInt(getWidth() - width);
int y = random.nextInt(getHeight() - height);
shapeList.add(new Rectangle(x, y, width, height));
repaint();
}
}).start();
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawString("BLAH", 20, 20);
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2.setStroke(STROKE);
for (Shape shape : shapeList) {
g2.setColor(FILL_COLOR);
g2.fill(shape);
g2.setColor(BORDER_COLOR);
g2.draw(shape);
}
}
}
public static void main(String args[]) {
EventQueue.invokeLater(new Runnable() {
public void run() {
new JavaPaintUI().setVisible(true);
}
});
}
}
Edit
You ask:
Now the problem is, I intend to draw a binary tree. The drawing mechanism works this way: I pass the tree's root to the drawing function, which will iterate through it, and draw a tree on the panel. I use drawString, drawOval and drawLine functions, which seems to be hard to implement this way. Do you have a solution for it maybe?
Actually I've given you the perfect solution for this. The shapeList List<Shape> variable will accept anything that implements the Shape interface which means you can add Line2D, Ellipse2D and similar objects as well as text to it.
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