Spawning mutiple circles and make them move

问题

I'm trying to teach myself java and I "try" to code a little game.

I have a problem and I guess the solution is very simple but I'm struggling.

The basic idea is that I am controlling a circle and I want to spawn circles every 5 seconds at random locations within the boundries of my window . The circles should move towords the location of the circle that I'm controlling.

Here's what I have so far:

Window-Class:

package TestGame;
import java.awt.Graphics;

public class Window extends GameIntern{

    public void init(){
        setSize(854,480);   
        Thread th = new Thread(this);
        th.start();
        offscreen = createImage(854,480);
        d = offscreen.getGraphics();
        addKeyListener(this);
    }

    public void paint(Graphics g){
        d.clearRect(0,0,854,480);
        d.drawOval(x, y, 20, 20);
        g.drawImage(offscreen,0,0,this);
    }

    public void update(Graphics g){
        paint(g);
    }
}

GameIntern-Class:

package TestGame;


import java.applet.Applet;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

public class GameIntern extends Applet implements Runnable , KeyListener {

    public int x,y;
    public Image offscreen;
    public Graphics d;
    public boolean up,down,left,right;

    public void run() {
        x = 100;
        y = 100;

        while(true){
            if(left == true){
                if(x>=4){
                x-=4;
                }else{ x=0;}
                repaint();
            }
            if(right == true){
                if(x<=826){
                    x+=4;
                    }else{ x=830;}
                repaint();
            }
            if(up == true){
                if(y>=4){
                y-=4;
                }else{ y=0;}
                repaint();
            }
            if(down == true){
                if(y<=454){
                y+=4;
                }else{y=459;}
                repaint();
            }
            try {
                Thread.sleep(20);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public void keyPressed(KeyEvent e) {

        if(e.getKeyCode() == 37){
            left=true;
        }
        if(e.getKeyCode() == 38){
            up=true;
        }
        if(e.getKeyCode() == 39){
            right=true;
        }
        if(e.getKeyCode() == 40){
            down=true;
        }

    }


    public void keyReleased(KeyEvent e) {

        if(e.getKeyCode() == 37){
            left=false;
        }
        if(e.getKeyCode() == 38){
            up=false;
        }
        if(e.getKeyCode() == 39){
            right=false;
        }
        if(e.getKeyCode() == 40){
            down=false;
        }


    }

    public void keyTyped(KeyEvent e){}
}

I know it's nothing fancy but I'm struggling with how to create and spawn the "enemy"-circles and how to controll the x/y values of every single created circle to move towards the controllable circle.

Any form of help is appreciated.

回答1:

Note Using thread.sleep in a game is not a good idea. This is an example of a game loop with 60 iterations a second.

public void run() {
    double ns = 1000000000.0 / 60.0;
    double delta = 0;

    long lastTime = System.nanoTime();

    while (running) {
        long now = System.nanoTime();
        delta += (now - lastTime) / ns;
        lastTime = now;

        while (delta >= 1) {
            tick();
            delta--;
        }
    }
}

You would then need to move your code that controls your game into a tick() method. (or the equivalent)

private void tick() {
    if(left == true){
        if(x>=4){
            x-=4;
            }else{ x=0;}
            repaint();
        }
        if(right == true){
            if(x<=826){
                x+=4;
                }else{ x=830;}
            repaint();
        }
        if(up == true){
            if(y>=4){
            y-=4;
            }else{ y=0;}
            repaint();
        }
        if(down == true){
            if(y<=454){
            y+=4;
            }else{y=459;}
            repaint();
}

Answer I would make a new class containing the information for your enemies. It needs a constructor with an int x and int y and a tick() method.

public class Enemy {

    public enemy(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public void tick() {
    }
}

You can then make an ArrayList containing your enemies in your GameIntern class

private static ArrayList<Enemy> enemies = new ArrayList<Enemy>();

This allows you to have as many enemies as you want. You will need to update the enemies by calling all of their tick() methods with a for loop. The following needs to be added to the tick() method in GameIntern

for (Enemy e : enemies) {
    e.tick();
}

To add an enemy every 5 seconds with a random location inside of the screen you will need an int delay. The following is added to the tick() method in GameIntern

private int delay;
private Random random= new Random();

private void tick() {
    delay++;
    if(delay % (60 * 5) == 0)
        enemies.add(new Enemy(random.nextInt(your game width), random.nextInt(your game height));

To make the enemy chase you, add this to your tick() method in Enemy

if (x < GameIntern.x) x++;
if (x > GameIntern.x) x--;
if (y < GameIntern.y) y++;
if (y > GameIntern.y) y--;

For information about removing enemies see here

来源：https://stackoverflow.com/questions/30443458/spawning-mutiple-circles-and-make-them-move