Question

I’m creating a video game, and when I call the repaint() method, the entire screen updates and flashes irregularly. I have slightly fixed that problem, by specifying what’s repainted (charRect, which is a Rectangle object) in this line of code: repaint(charRect.x, charRect.y, 20, 32); The entire screen stops flashing, but the character is incredibly glitchy. I just need help to get the animation from moving (a and d) and jumping (w) to run smoothly.

import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import java.io.*;
import java.net.*;
import java.lang.*;
import static java.lang.Math.*;
import static java.lang.System.out;
import java.util.Random.*;
import javax.swing.JApplet;
import java.awt.Graphics;

public class UltimaBlade extends JApplet implements KeyListener
{
public final int        WIDTH = 900;
public final int        HEIGHT = 650;

public  int             score = 0;
private boolean         jumping = false;
private boolean         moveRight = false;
private boolean         moveLeft = false;
private boolean         jumpRight = false;
private boolean         jumpLeft = false;
private boolean         moveRightWhileJumping = false;
private boolean         moveLeftWhileJumping = false;

public  JFrame          JTitle = new JFrame("UltimaBlade"); 
        Image           characterImg = null;
        Image           blockImg1 = null;
        Image           floorImg1 = null;
        Image           wallImg1 = null;
             JLabel          scoreLabel = new JLabel("Score: " + score);

        Rectangle       charRect = new Rectangle(25, 450, 20, 32);
        Rectangle       blockRect1 = new Rectangle(25, 482, 30, 30);
        Rectangle       floorRect1 = new Rectangle(25, 482, 200, 1);CHANGE BACK TO 30
        Rectangle       wallRect1 = new Rectangle(55, 490, 1, 30);
        //Rectangle       tempGhost = new Rectangle(charRect.x, charRect.y, 20, 32);

public  JMenuBar        mb = new JMenuBar();
public  JMenu           menuFile = new JMenu("File");
public  JMenuItem       menuItemSave = new JMenuItem("Save");
public  JMenuItem       menuItemLoad = new JMenuItem("Load");
        Container       cont;
        Runner          runner;

public void init()
{
    setSize(WIDTH, HEIGHT);

    JTitle.setJMenuBar(mb);
    menuFile.add(menuItemSave);
    menuFile.add(menuItemLoad);
    mb.add(menuFile);
    JTitle.getContentPane().setLayout(new BorderLayout());
    menuItemSave.addActionListener(new ListenMenuSave());
    setJMenuBar(mb);
    new UltimaBlade();
}

public UltimaBlade()
{
    setLayout(null);
    setSize(WIDTH, HEIGHT);
    setVisible(true);

    cont = getContentPane();
    cont.setLayout(null);
    addKeyListener(this);
    cont.setBackground(Color.WHITE);

    cont.add(scoreLabel);
    scoreLabel.setBounds(50, 50, 100, 30);
    scoreLabel.setForeground(Color.BLACK);
    cont.setLayout(null);

    repaint();
    cont.validate();

    runner = new Runner();
    runner.start();
    setContentPane(cont);
}

public class ListenMenuSave implements ActionListener
{
    public void actionPerformed(ActionEvent e)
    {
        new Save();
    }
}

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

    try
    {
        URL     url1 = this.getClass().getResource("character.gif");       //Character
                characterImg = Toolkit.getDefaultToolkit().getImage(url1);
        URL     url2 = this.getClass().getResource("block.gif");           //Block
                blockImg1 = Toolkit.getDefaultToolkit().getImage(url2);
        URL     url3 = this.getClass().getResource("floor_line.gif");      //Floor Line
                floorImg1 = Toolkit.getDefaultToolkit().getImage(url3);
        URL     url4 = this.getClass().getResource("wall_line.gif");      //Wall Line
                wallImg1 = Toolkit.getDefaultToolkit().getImage(url4);
    }
    catch(Exception e)
    {

    }

    g.drawImage(characterImg, charRect.x, charRect.y, this);
    g.drawImage(floorImg1, floorRect1.x, floorRect1.y, this);
    g.drawImage(blockImg1, blockRect1.x, blockRect1.y, this);
    g.drawImage(wallImg1, wallRect1.x, wallRect1.y, this);
}

public void keyPressed(KeyEvent e)
{
    if(e.getKeyChar() == 'd' || e.getKeyChar() == 'D')
    {
        moveRight = true;
        if(jumping)
            moveRightWhileJumping = true;
    }
    if(e.getKeyChar() == 'a' || e.getKeyChar() == 'A')
    {
        moveLeft = true;
        if(jumping)
            moveLeftWhileJumping = true;
    }
}

public void keyReleased(KeyEvent e)
{
    if(e.getKeyChar() == 'd' || e.getKeyChar() == 'D')
    {
        moveRight = false;
        if(!jumping)
            moveRightWhileJumping = false;
    }
    if(e.getKeyChar() == 'a' || e.getKeyChar() == 'A')
    {
        moveLeft = false;
        if(!jumping)
            moveLeftWhileJumping = false;
    }
}

public void keyTyped(KeyEvent e)
{
    if(e.getKeyChar() == 'w' || e.getKeyChar() == 'W')
    {
        jumping = true;
    }
}

public class Runner extends Thread// implements Runnable
{
    public void run()
    {
        while(true)
        {
            try
            {
                int     j = 5;     //Beginning velocity
                double  t = 0;
                double  sum = j/5;
                while(jumping)
                {
                    repaint(charRect.x, charRect.y, 20, 32);
                    cont.validate();
                    int jump = (int)((-4.9 * ((t * t)/10)) + (j * t));
                    if(moveRightWhileJumping)
                    {
                        charRect.x = charRect.x + j; // Move Right while jumping.
                        if(charRect.intersects(wallRect1))
                        {
                            charRect.x = wallRect1.x - 21;
                            moveRightWhileJumping = false;
                        }
                    }
                    if(moveLeftWhileJumping)
                    {
                        charRect.x = charRect.x - j;  //Move Left while jumping.
                        if(charRect.intersects(wallRect1))
                        {
                            charRect.x = wallRect1.x + 1;
                            moveLeftWhileJumping = false;
                        }
                    }
                    if(jump > 0)
                    {
                        charRect.y = charRect.y - Math.abs(jump);
                        if(charRect.intersects(floorRect1))
                        {
                            charRect.y = floorRect1.y - 32;
                            jumping = false;
                            moveRightWhileJumping = false;
                            moveLeftWhileJumping = false;
                            break;
                        }
                    }
                    else if(jump < 0)
                    {
                        charRect.y = charRect.y + Math.abs(jump);
                        if(charRect.intersects(floorRect1))
                        {
                            charRect.y = floorRect1.y - 32;
                            jumping = false;
                            moveRightWhileJumping = false;
                            moveLeftWhileJumping = false;
                            break;
                        }
                    }
                    else
                    {
                        if(charRect.intersects(floorRect1))
                        {
                            charRect.y = floorRect1.y - 32;
                            jumping = false;
                            moveRightWhileJumping = false;
                            moveLeftWhileJumping = false;
                            break;
                        }
                    }

                    t++;
                    Thread.sleep(30);
                }


                while(moveLeft)
                {
                    repaint(charRect.x, charRect.y, 20, 32);
                    cont.validate();
                    charRect.x = charRect.x - j;  //Move Left speed.
                    if(charRect.intersects(wallRect1))
                    {
                        charRect.x = wallRect1.x + 1;
                    }
                    if(charRect.intersects(floorRect1))
                    {
                        charRect.y = floorRect1.y - 32;
                        jumping = false;
                        moveRightWhileJumping = false;
                        moveLeftWhileJumping = false;
                        break;
                    }
                    t++;
                    Thread.sleep(30);
                }


                while(moveRight)
                {
                    repaint(charRect.x, charRect.y, 20, 32);
                    cont.validate();
                    charRect.x = charRect.x + j;  //Move Left speed.
                    if(charRect.intersects(wallRect1))
                    {
                        charRect.x = wallRect1.x + 1;
                    }
                    if(charRect.intersects(floorRect1))
                    {
                        charRect.y = floorRect1.y - 32;
                        jumping = false;
                        moveRightWhileJumping = false;
                        moveLeftWhileJumping = false;
                        break;
                    }
                    t++;
                    Thread.sleep(30);
                }
            }
            catch(Exception e)
            {
                break;
            }
        }
    }
}

}

Answer 1

One of your main problems is that you’re painting directly in the paint(...) method JApplet itself rather in the paintComponent(...) method of a JPanel or JCompnent that is held by the applet. If you do the latter, you gain the benefit of Swing’s default double buffering, and that can make all the difference. Also, you can repaint a smaller Rectangle of the GUI by using one of the repaint(...) overloads, but this is of secondary importance. First you should solve your lack of double buffering problem.

Please start with this tutorial to learn the basics: Lesson: Performing Custom Painting

And then move on up to this article for more advanced information about drawing in Swing: Painting in AWT and Swing

Edit
Also, you should never read in files from within the paint(...) or paintComponent(...) methods as this will slow painting down and thereby reduce perceived responsiveness of your GUI several fold. Why not simply read in the files once and on applet startup, and then store their contents into a variable?