Linux中的ClassCastException但不包括Windows - DefaultMutableTreeNode

Question

這是問題所在。我有以下類擴展DefaultMutableTreeNode的FileNode

import javax.swing.tree.DefaultMutableTreeNode; 
import java.io.File; 

public class FileNode extends DefaultMutableTreeNode { 
    public FileNode(String Name, File File) { 
     super(Name); 
     this.Name = Name; 
     this.File = File; 
     this.isFolder = false; 
     CheckedOut = false; 
    } 

    public FileNode(String Name, File File, Boolean isFolder) { 
     super(Name); 
     this.Name = Name; 
     this.File = File; 
     this.isFolder = isFolder; 
     CheckedOut = false; 
    } 

    public Boolean CheckedOut; 
    public File File; 
    public String Name; 
    public Boolean isFolder; 
} 

我有一棵樹充滿了這些節點。

我得到一個轉換異常有以下幾點：

private class FileTreeCellRenderer extends DefaultTreeCellRenderer { 
    public Component getTreeCellRendererComponent(JTree tree, Object value, 
      boolean sel, boolean expanded, boolean leaf, 
      int row, boolean hasFocus) { 
     super.getTreeCellRendererComponent(tree, value, sel, expanded, leaf, 
      row, hasFocus); 
     FileNode fn = (FileNode)value; 
     Color nodeColor = Color.BLACK; 
     if (!fn.isFolder) { 
      if (fn.CheckedOut) { 
       nodeColor = Color.RED; 
      } else { 
       nodeColor = new Color(0,100,0); 
      } 
     } 
     setForeground(nodeColor); 
     return this; 
    } 
} 

奇怪的是，我只在Windows在Linux中得到這個錯誤不是。我在兩個平臺上運行相同的JRE - Oracle JDK 1.7.0_25

任何人有任何想法我做錯了什麼？

這裏是堆棧跟蹤：

Exception in thread "main" java.lang.ClassCastException: javax.swing.tree.DefaultMutableTreeNode cannot be cast to dropboxcheckout.FileNode 
    at dropboxcheckout.CheckoutPanel$FileTreeCellRenderer.getTreeCellRendererComponent(CheckoutPanel.java:115) 
    at javax.swing.plaf.basic.BasicTreeUI$NodeDimensionsHandler.getNodeDimensions(BasicTreeUI.java:2786) 
    at javax.swing.tree.AbstractLayoutCache.getNodeDimensions(AbstractLayoutCache.java:492) 
    at javax.swing.tree.VariableHeightLayoutCache$TreeStateNode.updatePreferredSize(VariableHeightLayoutCache.java:1359) 
    at javax.swing.tree.VariableHeightLayoutCache.updateNodeSizes(VariableHeightLayoutCache.java:917) 
    at javax.swing.tree.VariableHeightLayoutCache.invalidateSizes(VariableHeightLayoutCache.java:371) 
    at javax.swing.plaf.basic.BasicTreeUI.setCellRenderer(BasicTreeUI.java:385) 
    at javax.swing.plaf.basic.BasicTreeUI$Handler.propertyChange(BasicTreeUI.java:3390) 
    at java.beans.PropertyChangeSupport.fire(PropertyChangeSupport.java:335) 
    at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:327) 
    at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:263) 
    at java.awt.Component.firePropertyChange(Component.java:8382) 
    at javax.swing.JTree.setCellRenderer(JTree.java:759) 
    at dropboxcheckout.CheckoutPanel.<init>(CheckoutPanel.java:85) 
    at dropboxcheckout.CheckoutFrame.<init>(CheckoutFrame.java:37) 

Answer 1

沒有一個堆棧跟蹤轉儲，它很難看到問題正在發生，但假設它在你發佈的代碼，我猜它可能是你的FileNode。

我的建議是要妥善處理這個異常，無論什麼系統，其上運行...

private class FileTreeCellRenderer extends DefaultTreeCellRenderer { 
    public Component getTreeCellRendererComponent(JTree tree, Object value, boolean sel, boolean expanded, boolean leaf, int row, boolean hasFocus) { 
     super.getTreeCellRendererComponent(tree, value, sel, expanded, leaf, row, hasFocus); 

     Color nodeColor = Color.BLACK; 

     if (value instanceof FileNode){ 
      FileNode fn = (FileNode)value; 
      if (!fn.isFolder) { 
       if (fn.CheckedOut) { 
        nodeColor = Color.RED; 
       } 
       else { 
        nodeColor = new Color(0,100,0); 
       } 
      } 
     } 

     setForeground(nodeColor); 
     return this; 
    } 
} 

這一變化將檢查value是FileNode執行轉換之前。如果它不是FileNode，它將以黑色繪製該值，而不是在此時崩潰。

一般來說，它是在執行轉換之前檢查的良好實踐，所以您可以在對象實際上不可轉換的機會中正確處理它。