Question

这是在必须从游戏中移除玩家时调用的方法。这两种方法都属于不同的类别。

GameboardGUI类

    Vector<Player> players = new Vector<Player>();

    public void removePlayerFromGame(Player playerToRemove)
        {
            //go through the playerToRemove's properties and reset all their variables
            for(int i = 0; i < playerToRemove.getPropertiesOwned().size(); i++)
            {
                //code to reset the player's properties to an unowned/unmodified state
            }
            //same with transports
            for(int i = 0; i < playerToRemove.getTransportsOwned().size(); i++)
            {
                //code to reset the player's transports to an unowned/unmodified state
            }
            //just updating the vector based on the playerToRemove's position
            if(players.get(0) == playerToRemove)
            {
                players.remove(playerToRemove);
                updatePlayerInformation();
            }
            else 
            {
                players.remove(playerToRemove);
                updatePlayerVector(players);
                updatePlayerInformation();
            }

        }

调用该方法的方法如下：如果当前玩家（来自我）登陆房产并且无法支付租金（即由于takefrombalance(1200);他们的余额达到0，目前硬编码为1200以使测试更容易）他们将在if语句中删除if(fromMe.isBankrupt())

物业类

GameboardGUI gui = new GameboardGUI();

public void payRent(Player fromMe, Player toYou, int rent)
    {
        //remove rent from the current player
        fromMe.takeFromBalance(1200);
        //add it to the owner
        toYou.addToBalance(rent);
        GameboardGUI.addGameFeedMessage(fromMe.getName() + " has paid " + rent + " in rent to " + toYou.getName());
        GameboardGUI.addGameFeedMessage(toYou.getName() + "'s balance is now " + toYou.getBalance());
        if(fromMe.isBankrupt())
        {
            //THIS IS THE CALL THAT THROWS THE NullPointerException
            gui.removePlayerFromGame(fromMe);
        }
        else 
        {
            GameboardGUI.addGameFeedMessage(fromMe.getName() + "'s balance is now " + fromMe.getBalance());
        }
    }

这是到达行时的堆栈跟踪：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at PropertyTile.payRent(PropertyTile.java:254)
    at PropertyTile.landedOnProperty(PropertyTile.java:239)
    at GameboardGUI.playerHasLanded(GameboardGUI.java:1905)
    at Player.setPosition(Player.java:82)
    at Player.movePlayer(Player.java:101)
    at GameboardGUI$11.actionPerformed(GameboardGUI.java:1536)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$000(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

如果没有堆栈跟踪和代码的行号，真的很难帮助你，但我们正在尝试。

如果那是真的那条线（实际上不在removePlayerFromGame内），则成员gui尚未初始化。

当然，如果它不是那条线，那么它可能就是playerToRemove为空，而NullPointerException实际上发生在上面几行。

或者，另一种可能性是它发生在removePlayerFromGame内，在这种情况下，最可能的情况是playerToRemove尚未正确设置 - 其getPropertiesOwned()或{{ 1}}方法返回null。

Answer 2

我会添加以下两行，作为第一步，看看会发生什么：

if(fromMe==null)
System.out.println("from me is null");

if(gui == null)
System.out.println("gui is null"); 

gui.removePlayerFromGame(fromMe);

两个对象引用之一为null，导致异常。否则，方法removePlayerFromGame正在做一些事情，但我认为情况并非如此，因为stacktrace将包含其他方法。

Answer 3

你在代码中说到达到行

时抛出了异常

gui.removePlayerFromGame(fromMe);

但是，您显示的堆栈跟踪的顶部是Player.movePlayer（），其底部位于PropertyTile.payRent（）。

这个payRent（）接收任何参数吗？你可以发布消息来源吗？

NullPointerException我无法解决

3 个答案: