有人，请给我解释一下它是如何工作的。这是代码：

package checkboxtree;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Font;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.awt.event.MouseEvent;
import java.util.EventObject;
import java.util.Vector;

import javax.swing.AbstractCellEditor;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.UIManager;
import javax.swing.event.ChangeEvent;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeCellRenderer;
import javax.swing.tree.TreeCellEditor;
import javax.swing.tree.TreeCellRenderer;
import javax.swing.tree.TreePath;

public class CheckBoxNodeTreeSample {
  public static void main(String args[]) {
    JFrame frame = new JFrame("CheckBox Tree");

    CheckBoxNode accessibilityOptions[] = {
        new CheckBoxNode(
            "Move system caret with focus/selection changes", false),
        new CheckBoxNode("Always expand alt text for images", true) };
    CheckBoxNode browsingOptions[] = {
        new CheckBoxNode("Notify when downloads complete", true),
        new CheckBoxNode("Disable script debugging", true),
        new CheckBoxNode("Use AutoComplete", true),
        new CheckBoxNode("Browse in a new process", false) };
    Vector accessVector = new NamedVector("Accessibility",
        accessibilityOptions);
    Vector browseVector = new NamedVector("Browsing", browsingOptions);
    Object rootNodes[] = { accessVector, browseVector };
    Vector rootVector = new NamedVector("Root", rootNodes);
    JTree tree = new JTree(rootVector);

    CheckBoxNodeRenderer renderer = new CheckBoxNodeRenderer();
    tree.setCellRenderer(renderer);

    tree.setCellEditor(new CheckBoxNodeEditor(tree));
    tree.setEditable(true);

    JScrollPane scrollPane = new JScrollPane(tree);
    frame.getContentPane().add(scrollPane, BorderLayout.CENTER);
    frame.setSize(300, 150);
    frame.setVisible(true);
  }
}

class CheckBoxNodeRenderer implements TreeCellRenderer {
  private JCheckBox leafRenderer = new JCheckBox();

  private DefaultTreeCellRenderer nonLeafRenderer = new DefaultTreeCellRenderer();

  Color selectionBorderColor, selectionForeground, selectionBackground,
      textForeground, textBackground;

  protected JCheckBox getLeafRenderer() {
    return leafRenderer;
  }

  public CheckBoxNodeRenderer() {
    Font fontValue;
    fontValue = UIManager.getFont("Tree.font");
    if (fontValue != null) {
      leafRenderer.setFont(fontValue);
    }
    Boolean booleanValue = (Boolean) UIManager
        .get("Tree.drawsFocusBorderAroundIcon");
    leafRenderer.setFocusPainted((booleanValue != null)
        && (booleanValue.booleanValue()));

    selectionBorderColor = UIManager.getColor("Tree.selectionBorderColor");
    selectionForeground = UIManager.getColor("Tree.selectionForeground");
    selectionBackground = UIManager.getColor("Tree.selectionBackground");
    textForeground = UIManager.getColor("Tree.textForeground");
    textBackground = UIManager.getColor("Tree.textBackground");
  }

  public Component getTreeCellRendererComponent(JTree tree, Object value,
      boolean selected, boolean expanded, boolean leaf, int row,
      boolean hasFocus) {

    Component returnValue;
    if (leaf) {

      String stringValue = tree.convertValueToText(value, selected,
          expanded, leaf, row, false);
      leafRenderer.setText(stringValue);
      leafRenderer.setSelected(false);

      leafRenderer.setEnabled(tree.isEnabled());

      if (selected) {
        leafRenderer.setForeground(selectionForeground);
        leafRenderer.setBackground(selectionBackground);
      } else {
        leafRenderer.setForeground(textForeground);
        leafRenderer.setBackground(textBackground);
      }

      if ((value != null) && (value instanceof DefaultMutableTreeNode)) {
        Object userObject = ((DefaultMutableTreeNode) value)
            .getUserObject();
        if (userObject instanceof CheckBoxNode) {
          CheckBoxNode node = (CheckBoxNode) userObject;
          leafRenderer.setText(node.getText());
          System.out.println("setting state");
          System.out.println(node.getText());
          System.out.println(node.isSelected());
          leafRenderer.setSelected(node.isSelected());
        }
      }
      returnValue = leafRenderer;
    } else {
      returnValue = nonLeafRenderer.getTreeCellRendererComponent(tree,
          value, selected, expanded, leaf, row, hasFocus);
    }
    return returnValue;
  }
}

class CheckBoxNodeEditor extends AbstractCellEditor implements TreeCellEditor {

  CheckBoxNodeRenderer renderer = new CheckBoxNodeRenderer();
  public static int clickCount = 0;

  ChangeEvent changeEvent = null;

  JTree tree;

  public CheckBoxNodeEditor(JTree tree) {
    this.tree = tree;
  }

  public Object getCellEditorValue() {
      System.out.println("getCellEditorValue method called!");
    JCheckBox checkbox = renderer.getLeafRenderer();
    CheckBoxNode checkBoxNode = new CheckBoxNode(checkbox.getText(),
        checkbox.isSelected());
    return checkBoxNode;
  }

  public boolean isCellEditable(EventObject event) {

      System.out.println("isCellEditable method called");

      boolean returnValue = false;
    if (event instanceof MouseEvent) {
      MouseEvent mouseEvent = (MouseEvent) event;
      TreePath path = tree.getPathForLocation(mouseEvent.getX(),
          mouseEvent.getY());
      if (path != null) {
        Object node = path.getLastPathComponent();
        if ((node != null) && (node instanceof DefaultMutableTreeNode)) {
          DefaultMutableTreeNode treeNode = (DefaultMutableTreeNode) node;
          Object userObject = treeNode.getUserObject();
          returnValue = ((treeNode.isLeaf()) && (userObject instanceof CheckBoxNode));
        }
      }
    }
    return returnValue;
  }

  public Component getTreeCellEditorComponent(JTree tree, Object value,
      boolean selected, boolean expanded, boolean leaf, int row) {

      System.out.println("getTreeCellEditorComponent method called!");

      System.out.println(String.valueOf(clickCount++));

    Component editor = renderer.getTreeCellRendererComponent(tree, value,
        true, expanded, leaf, row, true);

    // editor always selected / focused
    ItemListener itemListener = new ItemListener() {
      public void itemStateChanged(ItemEvent itemEvent) {
          JCheckBox item = (JCheckBox)itemEvent.getItem();
          System.out.println(itemEvent.paramString());
          System.out.println("item "+item.getText()+" state Changed!");

          if (stopCellEditing()) {
              fireEditingStopped();
          }
      }
    };
    if (editor instanceof JCheckBox) {
      ((JCheckBox) editor).addItemListener(itemListener);
    }

    return editor;
  }
}

class CheckBoxNode {
  String text;

  boolean selected;

  public CheckBoxNode(String text, boolean selected) {
    this.text = text;
    this.selected = selected;
  }

  public boolean isSelected() {
    return selected;
  }

  public void setSelected(boolean newValue) {
    selected = newValue;
  }

  public String getText() {
    return text;
  }

  public void setText(String newValue) {
    text = newValue;
  }

  public String toString() {
    return getClass().getName() + "[" + text + "/" + selected + "]";
  }
}

class NamedVector extends Vector {
  String name;

  public NamedVector(String name) {
    this.name = name;
  }

  public NamedVector(String name, Object elements[]) {
    this.name = name;
    for (int i = 0, n = elements.length; i < n; i++) {
      add(elements[i]);
    }
  }

  public String toString() {
    return "[" + name + "]";
  }
}

这是输出：

isCellEditable method called
getTreeCellEditorComponent method called!
0
setting state
Use AutoComplete
true
ITEM_STATE_CHANGED,item=javax.swing.JCheckBox[,40,84,129x24,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@b179c3,flags=296,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],paintBorder=false,paintFocus=false,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Use AutoComplete],stateChange=DESELECTED
item Use AutoComplete state Changed!
getCellEditorValue method called!
setting state
Use AutoComplete
false
setting state
Use AutoComplete
false
setting state
Use AutoComplete
false

isCellEditable method called
getTreeCellEditorComponent method called!
1
setting state
Use AutoComplete
false
ITEM_STATE_CHANGED,item=javax.swing.JCheckBox[,40,84,129x24,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@b179c3,flags=296,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],paintBorder=false,paintFocus=false,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Use AutoComplete],stateChange=SELECTED
item Use AutoComplete state Changed!
getCellEditorValue method called!
setting state
Use AutoComplete
true
ITEM_STATE_CHANGED,item=javax.swing.JCheckBox[,40,84,129x24,invalid,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@b179c3,flags=296,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],paintBorder=false,paintFocus=false,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Use AutoComplete],stateChange=SELECTED
item Use AutoComplete state Changed!
setting state
Use AutoComplete
true
setting state
Use AutoComplete
true

isCellEditable method called
getTreeCellEditorComponent method called!
2
ITEM_STATE_CHANGED,item=javax.swing.JCheckBox[,40,84,129x24,invalid,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@b179c3,flags=296,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],paintBorder=false,paintFocus=false,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=checkboxtree.CheckBoxNode[Use AutoComplete/true]],stateChange=DESELECTED
item checkboxtree.CheckBoxNode[Use AutoComplete/true] state Changed!
ITEM_STATE_CHANGED,item=javax.swing.JCheckBox[,40,84,129x24,invalid,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@b179c3,flags=296,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],paintBorder=false,paintFocus=false,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=checkboxtree.CheckBoxNode[Use AutoComplete/true]],stateChange=DESELECTED
item checkboxtree.CheckBoxNode[Use AutoComplete/true] state Changed!
setting state
Use AutoComplete
true
ITEM_STATE_CHANGED,item=javax.swing.JCheckBox[,40,84,129x24,invalid,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@b179c3,flags=296,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],paintBorder=false,paintFocus=false,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Use AutoComplete],stateChange=SELECTED
item Use AutoComplete state Changed!
ITEM_STATE_CHANGED,item=javax.swing.JCheckBox[,40,84,129x24,invalid,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@b179c3,flags=296,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],paintBorder=false,paintFocus=false,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Use AutoComplete],stateChange=SELECTED
item Use AutoComplete state Changed!
ITEM_STATE_CHANGED,item=javax.swing.JCheckBox[,40,84,129x24,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@b179c3,flags=296,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],paintBorder=false,paintFocus=false,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Use AutoComplete],stateChange=DESELECTED
item Use AutoComplete state Changed!
getCellEditorValue method called!
setting state
Use AutoComplete
false
ITEM_STATE_CHANGED,item=javax.swing.JCheckBox[,40,84,129x24,invalid,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@b179c3,flags=296,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],paintBorder=false,paintFocus=false,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Use AutoComplete],stateChange=DESELECTED
item Use AutoComplete state Changed!
ITEM_STATE_CHANGED,item=javax.swing.JCheckBox[,40,84,129x24,invalid,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@b179c3,flags=296,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],paintBorder=false,paintFocus=false,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Use AutoComplete],stateChange=DESELECTED
item Use AutoComplete state Changed!
setting state
Use AutoComplete
false
setting state
Use AutoComplete
false

我不明白为什么法 getTreeCellRendererComponent 的方法之后三次叫
getCellEditorValue 。

以及为什么当我单击它时， JCheckbox会 生成那么多 ITEM_STATE_CHANGED 事件。