Styjun

I have made 2 JPanels, Panel and BackGround, in a JFrame. I am dynamically painting the Panel after 10ms(using a Timer), but the BackGround is only painted once at the beginning of the game. The Panel is responsible for the displaying of the fighters(spacecrafts), the projectiles and the aliens. The BackGround is responsible for the displaying of the background scene which is non-dynamic. The paintComponent(Graphics) method does paint the fighters and the projectiles, but flickers when they are updating. Can someone find the cause.

This is my Frame:

import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class Frame extends JFrame 
 private static final long serialVersionUID = 1L;

 public static final int WIDTH = 1280;
 public static final int HEIGHT = 720;

 public static final int DELAY = 10;

 private Panel panel;
 private Background bg;

 public Frame() 

 panel = new Panel();
 bg = new Background();

 initComponents();
 

 public void initComponents() 

 this.setSize(WIDTH, HEIGHT);

 this.add(bg);
 this.add(panel);

 this.setLocationRelativeTo(null);
 this.setResizable(false);
 this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

 this.addKeyListener(new KeyAdapter() 

 @Override
 public void keyPressed(KeyEvent e) 
 if(e.getKeyCode() == KeyEvent.VK_LEFT) panel.moveLeft();
 else if(e.getKeyCode() == KeyEvent.VK_RIGHT) panel.moveRight();
 

 );

 

 public static void main(String args[]) 

 SwingUtilities.invokeLater(new Runnable() 
 @Override
 public void run() 
 new Frame().setVisible(true);
 
 );

 

This is my Panel:

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.JPanel;
import javax.swing.Timer;

public class Panel extends JPanel implements ActionListener 
 private static final long serialVersionUID = 1L;

 public static final int DELAY = Frame.DELAY;

 private Timer timer;
 private BufferedImage fighter;

 int x, y;

 public Panel() 

 timer = new Timer(DELAY, this);
 try 
 fighter = ImageIO.read(this.getClass().getResource("fighter.png"));
 catch (IOException e) 
 e.printStackTrace();
 

 initComponents();

 timer.start();
 

 public void initComponents() 

 this.setSize(Frame.WIDTH, Frame.HEIGHT);
 this.setDoubleBuffered(true);
 this.setBackground(new Color(0, 0, 0, 0));

 x = 150;
 y = 200;

 


 @Override
 public void paintComponent(Graphics g) 
 super.paintComponent(g);

 Graphics2D g2d = (Graphics2D) g;
 doDrawing(g2d);

 



 private void doDrawing(Graphics2D g2d) 

 g2d.drawImage(fighter, x, y, null);

 

 @Override
 public void actionPerformed(ActionEvent arg0) 

 this.repaint();
 

 public void moveLeft() 
 x -= 10;
 

 public void moveRight() 
 x += 10;
 

This is the BackGround:

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.JPanel;
import javax.swing.Timer;


public class Background extends JPanel implements ActionListener
 private static final long serialVersionUID = 1L;

 private BufferedImage backGround;
 private Timer timer;
 public Background() 

 this.setSize(Frame.WIDTH, Frame.HEIGHT);
 this.setBackground(new Color(0, 0, 0, 0));

 timer = new Timer(Frame.DELAY, this);

 try 
 backGround = ImageIO.read(this.getClass().getResource("background.png"));
 catch (IOException e) 
 e.printStackTrace();
 

 timer.start();

 

 @Override
 public void paintComponent(Graphics g) 
 super.paintComponent(g);

 g.drawImage(backGround, 0, 0, null);

 

 @Override
 public void actionPerformed(ActionEvent e) 

 this.repaint();

 

I expect the sprites not to flicker and not to lag(which is not happening after lots of trials).

1. Do not call repaint within a painting method


2. Get rid of the Background class and do all drawing in one JPanel. For example:


3. See example below of both as well as of MCVE design
   
   
   • whole thing can be copy/pasted into IDE and run
   
   
   • uses images available to all online, not on disk
   
   


4. I would also remove the Timer that simply calls repaint() and instead either
   
   
   • call repaint from within the KeyListener
   
   
   • or use the timer to do the actual sprite movement code (with repaint()). This would be useful if you want continuous movement
   
   

Example MCVE:

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;

import javax.imageio.ImageIO;
import javax.swing.*;

public class Frame1 extends JFrame 
 // Image attribution:
 // By Adam Evans - M31, the Andromeda Galaxy (now with h-alpha)
 // Uploaded by NotFromUtrecht, CC BY 2.0,
 // https://commons.wikimedia.org/w/index.php?curid=12654493
 public static final String ANDROMEDA_IMAGE = "https://upload.wikimedia.org/wikipedia/commons/"
 + "thumb/9/98/Andromeda_Galaxy_%28with_h-alpha%29.jpg/"
 + "1280px-Andromeda_Galaxy_%28with_h-alpha%29.jpg";
 public static final String SPRITE_IMAGE = "https://upload.wikimedia.org/wikipedia/commons/"
 + "thumb/a/a1/Glossy_3d_blue_blue2.png/" + "120px-Glossy_3d_blue_blue2.png";

 private static final long serialVersionUID = 1L;
 public static final int WIDTH = 1280;
 public static final int HEIGHT = 720;
 public static final int DELAY = 10;
 private Panel1 panel;
 // private Background bg;

 public Frame1() 
 panel = new Panel1();
 // bg = new Background();
 initComponents();
 

 public void initComponents() 
 this.setSize(WIDTH, HEIGHT);
 // this.add(bg);
 this.add(panel);
 this.setLocationRelativeTo(null);
 this.setResizable(false);
 this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 this.addKeyListener(new KeyAdapter() 
 @Override
 public void keyPressed(KeyEvent e) 
 if (e.getKeyCode() == KeyEvent.VK_LEFT)
 panel.moveLeft();
 else if (e.getKeyCode() == KeyEvent.VK_RIGHT)
 panel.moveRight();
 
 );
 

 public static void main(String args[]) 
 SwingUtilities.invokeLater(new Runnable() 
 @Override
 public void run() 
 new Frame1().setVisible(true);
 
 );
 

class Panel1 extends JPanel implements ActionListener 
 private static final long serialVersionUID = 1L;
 public static final int DELAY = Frame1.DELAY;
 private Timer timer;
 private BufferedImage fighter;
 private BufferedImage background;
 int x, y;

 public Panel1() 
 timer = new Timer(DELAY, this);
 try 
 URL url = new URL(Frame1.SPRITE_IMAGE);
 // fighter = ImageIO.read(this.getClass().getResource("fighter.png"));
 fighter = ImageIO.read(url);

 url = new URL(Frame1.ANDROMEDA_IMAGE);
 background = ImageIO.read(url);

 catch (IOException e) 
 e.printStackTrace();
 
 initComponents();
 timer.start();
 

 public void initComponents() 
 this.setSize(Frame1.WIDTH, Frame1.HEIGHT);
 this.setDoubleBuffered(true);
 this.setBackground(new Color(0, 0, 0, 0));
 x = 150;
 y = 200;
 

 @Override
 public void paintComponent(Graphics g) 
 super.paintComponent(g);
 g.drawImage(background, 0, 0, this);
 g.drawImage(fighter, x, y, this);
 

 @Override
 public void actionPerformed(ActionEvent arg0) 
 this.repaint();
 

 public void moveLeft() 
 x -= 10;
 

 public void moveRight() 
 x += 10;