【随手笔记——JAVA】发射子弹

public class Dan{
    private int x;
    private int y;

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

    public void paint(Graphics g) {
        if(y >= 720){
            y = 0;
            //Dans.getInstance().getDans().remove(this);
        }
        g.drawOval(x, y+=1, 10, 10);
    }

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }

    public int getY() {
        return y;
    }

    public void setY(int y) {
        this.y = y;
    }

}

public class Dans {

    List<Dan> dans;
    private static Dans instance;

    private Dans() {
        dans = new ArrayList<>();
    }

    public static Dans getInstance() {
        if (instance == null) {
            instance = new Dans();
        }
        return instance;
    }

    public List<Dan> getDans() {
        return dans;
    }

}

public void paint(Graphics g) {
        super.paint(g);    
        mTanKe.paint(g);
        for(Dan dan : dans){
            dan.paint(g);
        }