什么是有关此线程/油漆异常？

Question

我玩的事情，我真的不明白，在探索未知领域的时刻在机器人Java项目（有效位置的网格和阻塞位置）。无论如何，我试图改善我们给出的如何进行，它已与文本字段和各种Unicode字符表示的地图和机器人操作的示例，基本GUI。我试图通过覆盖paint方法和绘图彩色矩形屏幕来在地图去做。当程序启动时，我提出与下面的运行时异常，但窗口加载了（虽然由于某些原因在上面这些Jbutton都看不见，直到我摇我的鼠标移到他们）和功能精细从那时起。

我远远的试验和错误，并结合实例玩这个了，我在网上找到的，但我想有一些基本的东西在这里我没有把握。

感谢您能在这里给我任何建议。

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at Controller.paint(Controller.java:156)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.seqPaintDirtyRegions(Unknown Source)
    at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(Unknow
n Source)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at Controller.paint(Controller.java:156)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.seqPaintDirtyRegions(Unknown Source)
    at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(Unknow
n Source)
    at java.awt.event.InvocationEvent.dispatch(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

我建议您通过阅读 Swing指南启动。它包含说明画是如何完成的部分。对于一件事你应该重写的paintComponent（）方法。从上面的错误出现的代码是在涂料（）方法。

要学习的东西，你应该从小事做起，那么当你有问题，你可以发布 SSCCE 显示的问题。