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確定，所以我已創建將充當移動傳球，反彈的牆壁和其他NanOrgs碰撞在Java其它目的
一個
NanOrg
對象此程序`公開課NanOrg擴展Ellipse2D.Float {
public int x_speed, y_speed;
private int d;
private int width = MainWindow.WIDTH;
private int height = MainWindow.HEIGHT;
private ArrayList<NanOrg> nanorgs;
Rectangle2D r = new Rectangle2D.Float(super.x, super.y, d, d);
public NanOrg(int diameter, ArrayList<NanOrg> nanorgs){
super((int) (Math.random() * (MainWindow.WIDTH - 20) + 1), (int) (Math.random() * (MainWindow.HEIGHT - 20) + 1), diameter, diameter);
this.d = diameter;
this.x_speed = (int) (Math.random() * 5 + 1);
this.y_speed = (int) (Math.random() * 5 + 1);
this.nanorgs = nanorgs;
}
public void move(){
for(NanOrg nanorg : nanorgs){
if(nanorg != this && nanorg.intersects(r)){
int tempx = x_speed;
int tempy = y_speed;
x_speed = nanorg.x_speed;
y_speed = nanorg.y_speed;
nanorg.x_speed = tempx;
nanorg.y_speed = tempy;
break;
}
}
if(super.x < 0){
super.x = 0;
x_speed = Math.abs(x_speed);
}
else if(super.x > width - d){
super.x = width - d;
x_speed = -Math.abs(x_speed);
}
if(super.y < 0){
super.y = 0;
y_speed = Math.abs(y_speed);
}
else if(super.y > height - d){
super.y = height - d;
y_speed = -Math.abs(y_speed);
}
super.x += x_speed;
super.y += y_speed;
}
}`an D，它代表的油動不動液滴的
油
對象。
public class Oil extends Ellipse2D.Float {
private int width = MainWindow.WIDTH;
private int height = MainWindow.HEIGHT;
private int d;
private ArrayList<Oil> oils;
Rectangle2D rect = new Rectangle2D.Float(super.x, super.y, d, d);
public Oil(int diameter){
super((int) (Math.random() * (MainWindow.WIDTH - 20) + 1), (int) (Math.random() * (MainWindow.HEIGHT - 20) + 1), diameter, diameter);
this.d = diameter;
}
}
的NanOrgs在隨機位置產卵，並在隨機的方向和速度移動。 NanOrg能夠彼此反彈，但我需要幫助弄清楚如何處理油和NanOrg之間的碰撞，特別是NanOrg可以通過去除油來「吃」油。我有兩個其他類：
主窗口和PaintSurface
MainWindow類創建窗口爲JApplet的。
'公共類主窗口擴展JApplet的{
public static final int WIDTH = 500;
public static final int HEIGHT = 500;
private PaintSurface canvas;
public void init(){
this.setSize(WIDTH, HEIGHT);
this.setName("NanOrg Program");
canvas = new PaintSurface();
this.add(canvas, BorderLayout.CENTER);
Timer t = new Timer(20, e -> {canvas.repaint();});
t.start();
}
} The PaintSurface Class "draws" the Oil and NanOrgs公共類PaintSurface擴展JComponent的{
public ArrayList<NanOrg> nanorgs = new ArrayList<NanOrg>();
public ArrayList<Oil> oils = new ArrayList<Oil>();
public PaintSurface(){
for(int i = 0; i < 5; i++)
nanorgs.add(new NanOrg(10, nanorgs));
for(int o = 0; o < 30; o++)
oils.add(new Oil(10));
}
public void paint(Graphics g){
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.MAGENTA);
for(NanOrg nanorg : nanorgs){
nanorg.move();
g2.fill(nanorg);
}
for(Oil oil : oils){
g2.setColor(Color.BLACK);
g2.fill(oil);
}
}
}`
這是我的計劃，所以只需回顧一下：我有創造它，所以NanOrgs互相反彈和牆壁，但我需要幫助我需要編寫的NanOrg「吃」石油（如刪除它）和在哪裏放置刪除石油的代碼。我在NanOrg Class中嘗試過 public void eatOil(){ for(Oil oil : oils){ if(oil.intersects(r)){ oils.remove(oil); } } } ，然後在我的PaintSurface類中調用該方法，但是當我運行它時，出現NullPointerException。然後，我嘗試在Oil和PaintSurface類中執行相同的代碼，但是我無法讓這兩個類中的任何一個使用「r」作爲NanOrg中定義的變量。所以如果你能幫我弄清楚怎麼做會很棒，或者告訴我如果我做錯了什麼，該怎麼做。如果您有任何疑問可以嘗試澄清ypur知識，請詢問我將盡我所能回答。
縮小代碼並更具體 –
在for（E e：list）中調用正在被集成的ArrayList上的remove是不好的。考慮將無糖水滴複製到新的列表中，以取代舊的。 – laune
顯示堆棧跟蹤。 – DV88