我遇到了一個奇怪的問題,我很好奇(並希望找到解決方法)。在界面和類中聲明的常量之間的區別?
如果我宣佈我班的變量節點:
private static final String NODES = "nodes";
一切工作正常。
但是,如果我聲明在接口變量:
public interface MSMConstants {
public static final String NODES = "nodes";
}
和實施在使用變量節點的類接口, 我得到在我第一次使用節點的空指針異常。
關於這裏發生了什麼的任何想法?
線被崩潰:
lr_fontSize.setSelectedItem(((VisualItem)m_vis.getVisualGroup(NODES).tuples().next()).getFont().getSize());
SearchQueryBinding sq = new SearchQueryBinding((Table) m_vis.getGroup(NODES), "label",
(SearchTupleSet) m_vis.getGroup(Visualization.SEARCH_ITEMS));
第二個是一個構造函數中;第一個也在構造函數內部,但對於從第二個實例化的對象。請求
堆棧跟蹤:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at prefuse.data.query.SearchQueryBinding.<init>(SearchQueryBinding.java:53)
at edu.stanford.folding.msmexplorer.MSMExplorer.<init>(MSMExplorer.java:703)
at edu.stanford.folding.msmexplorer.MSMExplorer.graphView(MSMExplorer.java:1538)
at edu.stanford.folding.msmexplorer.MSMExplorer.graphView(MSMExplorer.java:1526)
at edu.stanford.folding.msmexplorer.MSMExplorer$1.actionPerformed(MSMExplorer.java:202)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:272)
at java.awt.Component.processMouseEvent(Component.java:6375)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6140)
at java.awt.Container.processEvent(Container.java:2083)
at java.awt.Component.dispatchEventImpl(Component.java:4737)
at java.awt.Container.dispatchEventImpl(Container.java:2141)
at java.awt.Component.dispatchEvent(Component.java:4565)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4619)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4280)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4210)
at java.awt.Container.dispatchEventImpl(Container.java:2127)
at java.awt.Window.dispatchEventImpl(Window.java:2482)
at java.awt.Component.dispatchEvent(Component.java:4565)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:684)
at java.awt.EventQueue.access$000(EventQueue.java:85)
at java.awt.EventQueue$1.run(EventQueue.java:643)
at java.awt.EventQueue$1.run(EventQueue.java:641)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
at java.awt.EventQueue$2.run(EventQueue.java:657)
at java.awt.EventQueue$2.run(EventQueue.java:655)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:654)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
我們可以看到如何/在哪裏使用NODES? – davidmontoyago 2012-08-08 20:33:52
你能告訴我們你如何訪問NODES嗎? – JamesB 2012-08-08 20:35:50
如果NODES已正確初始化,則NullPointerException與變量無關。我們可以看到StackTrace嗎? – davidmontoyago 2012-08-08 20:46:18