從不同的類訪問ArrayList

Question

嗯...我錯過了什麼嗎？ 嘗試從ArrayList中繪製導彈對象，但在調用p.missilies.size（）時不斷收到錯誤NullPointerException。導彈肯定存在，並在Player類中實例化，但是如何從ActionMissile.class獲得對它的訪問？

ActionMissile類

public class ActionMissile { 

public ArrayList<Missilies> missilies = new ArrayList<Missilies>(); 

public void paint(Graphics g, MainClass mc) { 
    url = mc.getDocumentBase(); 
    missile = mc.getImage(url, "missile.png"); 
    //missilies = p.getMissilies(); 
     for (int i = 0; i < p.missilies.size(); i++) { 
      Missilies m = new Missilies(mc); 
      m = (Missilies) p.missilies.get(i); 
      g.drawImage(missile, x, y, mc); 
     }  
    } 

主要類

ActionMissile a; 

public void init() 
{ 
    setSize(800, 600); 
    p = new Player(this); 
    e = new Enemy(this); 
    m = new Missilies(this); 
    a = new ActionMissile(); 

public void paint(Graphics g){ 
    p.paint(g, this); 
    e.paint(g, this); 
    if (!p.missilies.isEmpty()) 
     a.paint(g, this);  
} 

Player類

@Override 
public void keyPressed(KeyEvent e) { 
    switch (e.getKeyCode()){ 
    case KeyEvent.VK_SPACE:{ 

     if (lastKey == null || lastKey != e.getKeyChar()) { 
      lastKey = e.getKeyChar(); 
      Missilies m = new Missilies(x,y); 
      m.fire(); 
      missilies.add(m); 
      System.out.println("Missilies "+missilies);    

Answer 1

變化：

p.missilies.size() 

收件人：

mc.p.missiles.size() 

你想檢查mc中p的導彈。

這個樣子，因爲你調用的方法：

if (!p.missilies.isEmpty()) 
    a.paint(g, this);  

該代碼是在三菱商事。該代碼中的p也屬於mc。