Java帮助：使图像在屏幕上移动

Question

I've been having trouble with this for quite a while now I am trying to make a space shooter but to no avail, I'm trying to make the bullet move across the screen like in space invaders etc when the player presses the space bar a bullet should appear where the player's X position is and move right across the screen.

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.ImageIcon;
import javax.swing.JFrame;
public class game extends JFrame{

boolean run = true;
boolean fired = false;

Image player;
Image bullet;

int playerX = 100;
int playerY = 200;

int bulletX;
int bulletY;


public game(){
    //Load Images:
    ImageIcon playerI = new     ImageIcon("C:/Users/Dan/workspace/shooterProject/bin/shooterProject/ship.png");
    player = playerI.getImage();
    ImageIcon bulletI = new     ImageIcon("C:/Users/Dan/workspace/shooterProject/bin/shooterProject/bullet.png");
    bullet = bulletI.getImage();
    //Set up game

      addKeyListener(new AL());

       addMouseListener(new Mouse());

       init();

}

private Image dbImage;
private Graphics dbg;


public static void main(String[] args) {
  new game();
}


//When the program runs, thins are initialised here

public void init(){
    windowManager();
}
public void paintComponent(Graphics g){

    if(run == true){
        g.drawImage(player, playerX, playerY, this);
    }
    if(fired == true){
        g.drawImage(bullet, bulletX, bulletY, this);
    }

    repaint();

}

public void paint(Graphics g){
    dbImage = createImage(getWidth(), getHeight());
    dbg = dbImage.getGraphics();
    paintComponent(dbg);
    g.drawImage(dbImage,0,0,this);
}


public void bullet(){
    bulletX = playerX;
    bulletY = playerY;
    while(fired == true){
        bulletX = bulletX + 10;
        if(bulletX == 800){
            bullet = null;
            fired = false;
        }
    }

}


public void windowManager(){

      JFrame f = new JFrame();

      setTitle("Engine");
      setVisible(true);
      setResizable(false);
      setSize(800,400);
      setBackground(Color.BLACK);
      setDefaultCloseOperation(EXIT_ON_CLOSE);
}
public class AL extends KeyAdapter{
    public void keyPressed(KeyEvent e){

        int keyCode = e.getKeyCode();
        if((keyCode == KeyEvent.VK_UP) && (run == true) && (playerY - 20 > 0)){
               playerY = playerY - 10;
        }else if((keyCode == KeyEvent.VK_DOWN) && (run == true) && (playerY + 20 < 400)){
            playerY = playerY + 10;
        }
        if((keyCode == KeyEvent.VK_SPACE) && (fired == false)){
            fired = true;
            if(fired == true){
                bullet();
            }
        } 
    }

    public void keyReleased(KeyEvent e){
    }
}

public class Mouse extends MouseAdapter {
public void mousePressed(MouseEvent e) {

    double x = e.getX();
    double y = e.getY();

}
}
}

HOWEVER

When I run the code without the while loop the bullet appears at the player's X position but When the while loop is there when the player presses the X button nothing happens, the bullet doesnt even appear!

would anybody be able to assist me in how i can make the bullet appear and move across the screen? thanks

Answer 1

This is because you are not drawing the bullet until it's out of range, you should not use the while loop this way, you probably need to google for 'Game Loop' but until you do here is a snipet that may help, Note that very bad but should work:

public void paintComponent(Graphics g){

    if(run == true){
        g.drawImage(player, playerX, playerY, this);

        if(fired == true) {
            bulletX = bulletX + 10;
            if(bulletX > 800 || bulletX < 0){
                fired = false;
            }

            g.drawImage(bullet, bulletX, bulletY, this);
        }

        repaint();
    }

}

public void bullet(){
    bulletX = playerX;
    bulletY = playerY;
}

one final note, move this code in the paint methode dbImage = createImage(getWidth(), getHeight()) to the constructor or the init() because you are creating a new image every frame.